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AISECT TUTORIALS : PHYSICS : SET-9 

CHAPTER - 1 

REFRACTION, TOTAL INTERNAL REFLECTION, LENSES, 

DISPERSION AND SPECTRA 

1. Refraction : When a ray of light enters from one 

medium to another there occurs a deviation of the 

ray from its path. This phenomenon is called 

refraction of light. When a ray passes from denser 

to rater medium, it bends away from normal and 

when it enters from rarer medium to denser 

medium, it bens towards the normal. 

In the figure shown, AO is incidnet ray, 

OB is refracted ray, 

N 1ON 2 is normal at the point of incidence. 

|AON 1 = i, is angle of incidence and 

|BON 2 = r, is angle of refraction. 

fig.1 

Deviation produced in refraction from the plane 

surface is δ = i – r (as i > r ) 

(1) 

If, however, the refraction occurs from denser to 

rarer medium r > i, δ = r – i. 

(a) Laws of refraction 

The following are the two laws of refraction 

(i) The incident ray, normal at the point of 

incidence and the refracted ray all lie in the same 

plane. 

(ii) The ratio of sine of angle of incidence to sine 

of angle of refraction is constant. 

That is, sin i 

sin r = 1 µ 2 

This is called Snell’s law. 1 µ 2 is called refractive 

index of medium (2) w.r. to medium (1). 1 µ 2 can 

also be expressed as 

1µ 2 = 

Speed of light in medium (1) 

Speed of light in medium (2) 

(b) Absolute refractive index. 

The refractive index of a medium with respect to 

vacuum is referred to as absolute refractive index. 

So when light passes from vacuum to a medium the 

refractive index 

vacuumµ medium = sin i 

sinr = Speed light in vacuum 

Speed of light in medium It 

is important to note that when a ray of light enters


from one medium to another, velocity of light and 

wavelength in the medium change but frequency 

of light remains unaltered. 

∴ vacuum µ medium = sin i 

sinr = C v = vλ 

vλ = λ λ 

and 1 µ 2 = sin i 

sin r = v1 

v2 = vλ 1 

= λ1 

vλ 2 λ2 

µ = 

Real depth 

Apparant depth 

(C) APPLICATION OF REFRACTION 

(i) The object is in denser medium and the 

observer is in rarer medium : The object O is in 

denser medium. A ray of light OB, is incident at B 

at the interface of the denser and rarer medium. It 

is refracted away from the normal. The refracted 

ray, when produced backward meets the ray OA 

(along normal and hence refracted undevlared) at 

I. Therefore, I is the virtual image of O.AO is the 

real depth and AI is the apparent depth of the object 

from the interface. 

Now, from figure 

dµ r = sin i 

sin r = tan i AB × AI 

= 

tan r AO × AB 

[because sin θ = tan θ, if the angles are small] 

or 

rµ d = AO 

AI = Real depth 

Apparent depth 

∴ The shift of image = ⎛ ⎜ 

⎝ 

µ − 1) 

µ 

⎞ 

⎟ d 

⎠ 

Where µ is the refractive index of denser medium 

with respect to rarer medium and d is the real depth. 

(ii) Object in rarer medium and observer in 

denser medium : 

Object O is in rarer medium. A ray of light is 

incident in direction OB. It is refracted in direction 

BC. Another ray OA (incident normally) is 

refracted as such. The two refracted rays meet at I, 

therefore I is the virtual image of O 

From the figure : 

fig.2 

rµ d = sin i 

sin r = tan i AB × AI 

= 

tan r AO × AB 

rµ d = AI Apparent height 

= 

AO Real height 

The shift of the image : 

= AI – AO = (µ – 1) h 

where m = refractive index of denser medium with 

respect to rarer medium, h = real height of the 

object. 

(iii) Refraction through a rectangular 

transparent block : When a light ray AB is 

incident on a reactangular block of any transparent 

medium, then, on emergence from the block, the 

light ray passes parallel to itself but is laterally 

deviated. The ray AB, emerges in the direction CE 

which is parallel to AB, produced forward. The 

lateral deviation δ is the perpendicualr distance CD 

between the incidence and refracted directions. 

From the geometry of the figure : 

δ = BC sin (i – r) 

In ∆ BMC, BM 

BC = cos r 

[in ∆ BDC] 

(2)


or 

or BC = 

Therefore, 

t 

BC = cos r 

δ = 

t 

cos r 

t sin (i–r) 

cos r 

If the angle of incidence is small, 

∴ 

Now from equation (1), 

δ = 

t (i − r) 

1 

.....(1) 

sin i ⇒ i, sin r ⇒ r, cos r →1 

sin i 

sin r = µ becomes i r = µ 

δ = t i ⎡ ⎢ 1 − r ⎤ 

⎣ 

i⎥ 

= t i ⎡ ⎢ 1 − 1 ⎤ 

⎦ ⎣ 

µ ⎥ ... (2) 

⎦ 

(iv) Twinkling of starts : The r.I. of atmosphere 

changes with height. Even at the same level, the 

refractive index of air varies periodically. The rays 

of light from a star are sometimes concentrated at 

a point when it apperars bright, next moment the 

concentration of rays star are sometimes 

concentrated at a point when it appears bright, next 

moment the concentration of rays decreases and 

the star appears faint. The planets being nearer, the 

amount of light received from them is greater and 

so the variation of brightness is not appreciable. 

(d) Refraction through a number of media 

Consider a ray of light AO1 be incident at the 

boundary separating media a and b, having angle 

of incidence i1 and let r1 be angle of refraction, 

then 

a µ b = 

sin i1 

sinr1 

.......(1) 

The ray O 1 O 2 falls incident at an angle of incidence 

i 2 at the boundary separating media ‘b’ and ‘c’ and 

if r 2 is the angle of refraction in media C. 

b µ c = sin r 1 

sin r 2 

....... (2) 

Ray O 1 O 3 emerges along O 3 B, in medium ‘a’, 

where the angle of emergence is e = i 

Then 

c µ c = sin r 2 

sin e = sin r 2 

sini 1 

....... (3) 

Multiply relations (1), (2) and (3) vertically 

a µb × b µc × c µa = sin i 1 

sinr 1 

× sin r 1 

sin r 2 

× sin r 2 

sin r 1 

= 1 

or a µb b µc = 1 

c µa 

= a µc 

fig. 3 

When a ray of light enters from one medium to 

another, there occurs a deviation of ray from its 

path. This phenomenon is called refraction of light. 

2. Total internal reflection 

Consider that light is travelling from an optically 

denser medium such as water or glass into optically 

rarer medium such as air. Suppose S is a point 

source of light in a medium of refractive index µ2 

> µ1. From Snell’s law 

µ 1 

µ 2 

= sin i 

sin r = sin i 1 

sin r 1 

= sin i 2 

sin r 2 

or µ 1 sin r 1 = µ 2 sin i1 and µ 2 sin r2 = µ2 sin i2 

As µ 2 > µ 1 ,sinr 1 > sin i 1 , r 1 > i 1 

(3) 

or sin r 2 > sin i 2, r> i 2


2µ1 = µ1 

µ2 = sin i 

sinr = sin i c 

sin90 = sin i c 

1 

Also µ = 1 µ2 = 1 1 

= 

2 µ1 sin i c 

∴ µ = 

1 

sin i c 

fig.4 

Thus angle of refraction is always greater than 

angle of incidence. As shown in the figure when 

the angle of incidence is gradually increased angle 

of refraction also increases i.e., 

when i = 0, r = 0 (ray 1); 

i = i1, r = r1 (ray 2); 

i = i2, r = r2 (ray 3) 

At a certain stage (ray 4) when the angle of 

incidence is such that the angle of refraction in the 

rarer medium is 90º. Such angle of incidence in the 

denser medium for which angle of refraction in 

rarer medium is 90º is called critical angle. In this 

case the refracted ray just grazes along the surface 

separating the two media. Any further increase in 

the angle of incidence will turn the refracted ray 

back into the same medium as for ray 5. This ray 

is said to be totally interally reflected. Thus total 

internal reflection takes place if. 

(i) The ray of light travels from denser medium to 

rarer medium and 

(ii) Angle of incidence is greater than critical angle 

(ic) which is defined as that angle of incidence in 

the denser medium for which angle of refraction in 

the rarer medium is 90º. 

Substituting i. = i c and r = 90º in the defining 

equation for refractive index 

(4) 

fig.5 

(a) Critical angle. That angle of incidence in the 

denser medium for which angle of refraction in 

rarer medium is 90º. 

µ = 

1 

sin c 

c = critical angle 

Conditions for total internal reflection to occur 

(1) Rays of light must proceed from denser to rarer 

medium. 

(2) Angle of incidence be greater than critical angle 

i.e., < c. 

(b) Applications of total internal reflection 

(i) field of vision of fish : A fish inside water 

cannot see the entire surface of the pond, instead in 

sees only a circular patch of light, because only 

those light rays which are incident within a cone of 

semivertex angle ‘C’ are refracted out of the water 

surface. All other rays are totally interally 

refrlected. (See figure). 

1 

Now, µ = 

sin C = √⎺⎺⎺⎺ r 2 + ⎺ h 2 

r 

The redias of the circular patch of light, 

r = 

fish. 

h 

where h is the depth of the 

√⎺(µ 2 − 1)


fig.6 

(ii) Looming : In very cold regions the lower layers 

of air are cooled so much that its density increases 

down wards rapidly. Rays from a distant object, 

bends more and more away from the normal and 

suffer total reflection. The rays then proceeds 

downwards dending more and more towars the 

normal and ultimately appear to an observer to be 

emanating from an object hanging inverted in the 

sky. 

(iii) The sun is visible before actual sunrise and 

after actual sunset because of atmospheric 

refraction. This time difference is about 2 minute 

and the apparent shift in the direction is by about 

0.5º. 

(iv) The total internal reflection is seen in diamond 

if cut suitably because its critical angle is small. 

(v) The 45º prism deflect a light ray totally either 

in 90º or 180º direction. 

(vi) Mirage– When light rays travel through the 

hot air in summer days, they are totally internally 

reflected. Thus, the inverted image of distant object 

is observed. 

3. LENS 

A lens may be defined as the portion of a 

transparent medium bounded by two curved 

surfaces or by one curved surface and the other 

plane surface. 

If the curved surfaces are spherical, then the lenses 

are called spherical lenses. 

(5) 

If one of the bounding curved surface is cylindrical 

then the lenses are called cylindrical lenses. 

Spherical lenses are of two types : 

(i) Convex or convergent lenses; (ii) Concave or 

Divergent lenses. 

Convex or convergent lenses are of three forms : 

(i) Double convex lens (ii) Plano-convex lens (iii) 

Convavo-convex lens. 

The distinguishing characteristic of a convex lens 

is that it is thicker at the centre than at edges. 

Focal length of convex lens is positive. 

Divergent Lenses are of three forms : 

(i) Double concave (ii) Plano-concave (iii) 

Convexo-concave 

The distinguishing characteristic of a concave lens 

is that it is thinner at the centre than at edges. 

Focal length of convave lens is negative. 

(a) Sign convention (Lens Makers Formula) 

If the media on both the sides of a lens are the same, 

then two focal lengths are equal i.e. f 1 = – f 2 

1 

f = (n′ – 1) ⎛ 1 

⎜ − 1 ⎞ 

⎝ 

R 1 R 2 ⎟⎠ = 1 v − 1 u 

The above relation is to be used with proper 

signs for R 1 and R 2 as follows– 

(i) Double-convex : R 1 is + ve, R 2 is – ve 

(ii) Plano-convex : R 1 is + ve, R 2 = ∞ 

(iii) Convavo– convex : Both are – ve or both + 

ve 

(iv) Double – convex : R 1 is – ve, R 2 is + ve 

(v) Plano -concave : R 1 is –ve, R 2 = ∞ 

(vi) Convexo–concave : Both are – ve, or both + 

ve 

Focal length for a lens depends on the colour of 

light 

f r > f v


(b) Power of lens 

Power of a lens is its ability to converge or diverage 

the rays of light. It is measured as the reciprocal of 

the focal length of a lens expressed in metres. Thus, 

Power of lens ‘‘P’’ = 

It is expressed in diopter (D) or m -1 

1 

f (metres) diopters 

One diopter is the power of a lens whose focal 

length is 1 metre. 

By convention, the power of a convex lens is 

positive while while that of a concave lens is 

negative. 

(c) Lens formula 

1 

f = 1 v − 1 where u = object distance from optical centre, 

u 

Magnification 

v = image distance from optical centre 

M = 1 o = v M = negative for real image, positive for virtual 

u 

image. 

(d) FORMATION OF IMAGE BY A LENS 

Convex Lens 

Position of object Ray diagram Position of image Nature and size of image 

1. At infinity At focus Real, inverted, extremely 

small 

2. Beyond 2F Between F and 2F Real, inverted, smaller than 

object 

3. At 2F At 2 F Real, ivverted, and same 

size as the object 

4. Between F and 2 F Beyond 2 F Real, inverted and 

magnified 

5. At F At infinity Real, inverted and 

extremely magnified 

(6)


6. With in pole and 

focus 

On the same side 

as the object 

Virtual, erect and magnified 

Note : As the object moves closer to the lens, the image moves away and away from it. The minimum 

distance between an object and its real image is 4 F. 

Convex Lens 

Position of object Ray diagram Position of image Nature and size 

1. At infinity At F (on the same 

side as the object) 

Virtual, erect and extremely 

diminished 

2. Between infinity 

and the lens 

Between the lens 

and F 

Virtual, erect and 

diminished 

(e) Focal length of two thin lenses in contact 

Consider two thin lenses which are in contact with 

each other. Suppose that their focal lengths are f 1 

and f 2 and that of combination is F. It is assumed 

that since the lenses are thin CC 1 and CC 2 are not 

significant in comparison to u, v and v’. 

If lens (2) were not present, lens (1) would produce 

an image of an object O at I’. Therefore, for lens 

(1) 

– 1 u + 1 v’ = 1 f 1 

............. (1) 

Lens (2) produces an image, at I, of light which is 

originally converting to I’, i.e., virtual object at I’ 

gives rise to a real image at I, we have for lens (2) 

– 1 v’ + 1 v = 1 f 2 

.......... (2) 

fig.15 

Adding (1) and (2) we have 

∴ 

1 

F = 1 f 1 

+ 1 f 2 

F is the focal length of combination f 1, f 2, focal 

lengths of individual lenses. 

(7)


(f) Refraction through a prism 

i + e = A + D 

r 1 + r 2 = A 

fig.18 

fig.16 

graph of i Vs D is shown 

i = e, D = D m 

µ = Sin (A + D m) 

Sin A ⁄ 2 

For a thin prism δ, (deviation) = (µ – 1) A 

f = D2 – x 2 

4D 

From the figure it is clear that 

∴ 

D = u + v and x = v – u 

u = D – x 

2 

, v = D + x 

2 

Since, the image is real 

1 

f = 1 v – 1 

–u = 2 

D + x + 2 

D – x 

or f = D2 – x 2 

4D 

for one position of the lens 

x = 0, ∴ D = 4f 

i.e., the minimum distance between the object 

and its real image is 4f. 

fig.17 

(g) DISPLACEMENT METHOD 

Principle : If the distance between two pins is kept 

more than four times the focal length of a lens, then 

for two positions of a lens between the pins a real 

and inverted image of one pin is formed at the 

other. If the distance between the two positions of 

the lens is ‘x’ then the focal length of the lens is 

given by 

If 

x> 0, D> 4f. Thus the distance between the 

two pins should be more than 4f. 

If I 1 and I 2 are the heights of images in two 

positions of the lens, then from figure 

I 1 

O = v u ,I 2 

O = u v , 

whereAB = 0 = size of object. 

I 1 

I 2 

= v2 

u 2 and 

O = √⎺⎺⎺⎺ (I 1 I 2 ) 

that is, the length of the object is the geometric 

mean of the lengths of the two images. 

(h) Salient features relating to lenses– 

(8) 

(a) When a concave and a convex lenses are


(b) 

combined then the nature compound lens will 

be that of the lens of higher power. 

If a lens is cut to half then the image of an 

object formed by it will be complete but its 

intensity will comparatively decrease. 

(c) If the focal length of a lens of refractive index 

(d) 

µ and focal length in air f, becomes f’ on 

immersing it in a liquid of refractive index µ’ 

⎡µ − 1 ⎤ 

then f ’ ⎢ ⎥ 

= 

⎢ µ 

f ⎢ 

⎣ 

µ − 1 ⎥ 

⎥ 

⎦ 

For two thin lenses situated at a distance d 

apart (i) 1 f = 1 + 1 – d 

f 1 f 2 f 1 f 2 

(ii) P = P 1 + P 2 – dP 1 P 2 

(e) The numbers provided with spectacles 

represent their power. 

(f) 

(g) 

(h) 

On grinding a lens, its focal length increases 

and power decreases. 

The focal length of goggles is infinity and 

power is zero. 

The focal length of both types of lenses is less 

for blue light and it is more for red light. 

(4) Prism 

(i) 

(ii) 

An isotropic transparent medium closed by 

surfaces inclined at an angle (Fig. 19) is 

defined as a prism. 

fig.19 

The angle between the incident ray of light 

and the emergent ray (< TUS) is defined as 

(9) 

the angle of deviation. 

(a) Refraction through prism 

A prism produces deviation as well as dispersion. 

The path of a monochromatic light ray (consisting 

of single wavelength only) is shown in the adjacent 

diagram. 

In the diagram, PQ = incident ray, QR = refracted 

ray, RS = Emergent ray,


S m = angle of minimum deviation. 

For small prisms (having angle A ≈ 8º to 10º) : 

δ m = (µ − 1) A 

Since µ R


is dispersed. R represents red, Y represents yellow 

and V represents violet ray. The second prism 

deviates the rays in opposite direction. The yellow 

ray ‘Y’ takes and intermediate course and emerges 

out of the prism combination parallel to the 

incident ray, produced along ML. 

fig.22 

Now for such a combination : 

δ 1 + δ 2 = 0; or A A’ = − (µ’ y − 1) 

(µ y − 1) 

The total dispersion produced is : 

θ=θ 1 + θ 2 ; θ = δ 1 [ω 1 − ω 2 ] 

(ii) Deviation without dispersion (or achromatic 

combination of prisms) 

If two prisms, one of crown and the other of flint, 

are placed such that their angles are opposite to 

each other, and the prisms are such that the 

dispersion produced by one prism is equal and 

opposite to the dispersion produced by the other, 

then the incident ray passes undispersed through 

the prism system but it is deviated from its path. In 

this situation the net dispersion 

δ = δ 1 + δ 2 = θ 1 ⎡ ⎢ 

⎣ 

1 

ω 1 

− 1 ω 2 

⎤ 

⎥⎦ 

6. SPECTRUM :- 

(A) = The whole band of colours from violet to 

red colour is known as spectrum. 

(B) There are seven colours in the spectrum in the 

following order Violet (v), Indigo (i), Blue 

(b), Green (g), Yellow (y), Orange (o), red (r). 

(C) These colours can be remembered by the 

word VIBGYOR’ 

(D) 

Colour 

of light 

Wavele 

t e n g t h 

range of 

light (l) 

Freque 

ncy of 

light (v) 

V I 

Violet Indi 

go 

3 9 0 0 

Å 

4 5 5 0 

Å 

7.69-6 

.59 

x10 14 

Hz 

B 

Blue 

G 

Green 

4 5 5 0 4920Å 

Å 5770Å 

4 9 2 0 

Å 

6.59 

-6.10 

x10 14 

Hz 

6.10 

-5.20 

x10 14 

Hz 

Y 

Yell 

ow 

5770Å 

5970Å 

5.20 

-5.03 

x10 14 

Hz 

O R Red 

Orage 

5970Å 

6220Å 

5.03 

-4.82 

x10 14 

Hz 

6220Å 

7800Å 

4.82 

-3.84 

x10 14 

Hz 

(E) These seven colours are visible to our eyes 

hence these are known as visible colours and 

light is known as visible light. 

(F) 

The effect of light persists before our eyes for 

1 

second wherease effect of sound on ears 

16 

persists for 10 second. 

(G) The sensitivity of eye depends on wavelength 

of these colours. The eye is maximum 

sensitive for yellow colour. 

(H) The formation of rainbow and solar spectrum 

can be explained on the basis of dispersion. 

θ 1 + θ 2 = 0 ; 

or 

fig.23 

A 

A’ = – (µ’ v − µ’ R ) 

(µ v − µ R ) 

The total deviation produced is, 

(11) 

(I) 

In general spectra are divided into four classes 

broadly– 

(i) 

(ii) 

Real spectrum; 

Virtual spectrum; 

(iii) Impure spectrum and 

(iv) Pure spectrum.


Real spectrum– The spectrum which can be taken 

on the screen as produced by prism. 

Virtual spectrum– Rays emerging out from the 

prism when produced backward, appear to meet 

and such spectrum is virtual. It cannot be taken on 

screen. 

Impure spectrum– If there is overlapping of the 

colours in the spectrum, it is called impure 

spectrum. 

Pure spectrum– In the spectrum, if each colour is 

quite distinct and has sharp boundary, then it is 

called pure spectrum. Pure spectrum can be 

produced by the use of spectrometer. 

(J) Types of Spectra 

Spectra obtained from different ssubstances under 

different conditions are of two types– 

(i) Emission spectra and 

(ii) Absorption spectra. 

Emission spectra - The spectra obtained due to 

emission of light from a source is called emisston 

spectra. It is of three types - 

(a) Continuous spectrum - In this spectrum there 

is no sharp boundary of colours. It Is produced by 

red hot bodies, electric bulb, electric arc, flame of 

a lamp, red hot gases, sun, etc. 

(b) Band spectrum - when the substance emitting 

light due to its temperature, but It Is In the state of 

molecules, then the spectrum produced is called 

band spectrum or molecular spectrurm. It Is in the 

form of bands. Spectra produced by discharges 

tubes which contains gases at low pressure. 

(c) Line spectrum - It is also called atomic 

spectrum since matter emitting light Is in the form 

of atoms. In this spectrum, separate lines of 

different colours are observed. Sodium gives two 

lines D 1 and D 2 of wavelengths 5896 Å and 5890 

Å in yellow region. 

Absorption spectra - When light Is Incident on a 

transparent material, It absorbs few lines of Its 

spectra emitted by incident light. These dark lines 

are termed as absorption spectra The explanation 

is given by Kirchoffs law. 

According to Kirchoffs law, the material at low 

temperature absorbs those lines. which it can emit 

at high temperature. The absorption spectra is the 

characteristic of the material. 

7. Scattering of Light 

when the light is Incident on the particles, of which 

the size is smaller than wavelength of light 

(molecules) the scattering Is produced. In Rayleigh 

scattering, the scattered Intensity varies (1 λ 4 ) 

inversly to the fourth power of wavelength So the 

scattered light from very small particles is bluish 

(Tyndall effect). The blue colour of the sky is due 

to scattering by air molecules and the red sun is due 

to the removal of the blue by scattering from the 

direct beam. The Raman effect Involves scattering 

of photons by molecules. 

8. Rainbow 

It is a continuous spectrum of sunlight as one or 

more arcs in the sky with the observer at their 

centre. Water droplets acts as the dispersing 

system. The primary bow is due to one total 

internal reflection in the droplets and has an 

angular dispersion of 56’ at a mean altitude of 42º. 

The violet colour Is on the inside and red on the 

outside. 

The secondary bow is due to two internal 

reflections. It Is much fainter than the primary bow 

and has the red on the inside. Its angular dispersion 

is 1 0 32’ at a mean altitude of 51 0 . 

(12)


Objective Questions 

1. Formula for dispersive power is (where 

symbols have their usual meanings) 

or 

[MP PMT / PET] 

If the refractive indices of crown glass for red, 

yellow and violet colours are respectively 

µ r , µ y and µ v , then the dispersive power of 

this glass would be 

(a) µ v − µ y 

µ r − 1 

(b) µ v − µ r 

µ y − 1 

(c) µ v − µ y 

µ y − µ r 

(d) µ v − µ r 

µ y 

− 1 

[MP PMT] 

2. The critical angle between a equilateral prism 

and air is 42º. If the incident ray is 

perpendicular to the refracting surface, then 

[MP PMT] 

(a) After deviation it will emerge from the 

(b) 

(c) 

(d) 

second refracting surface 

It is totally reflected on the second 

surface and emerges out 

perpendicularly from third surface in air 

It is totally reflected from the second 

and third refracting surfaces and finally 

emerges out from the first surface 

It is totally reflected from all the three 

sides of prism and never emerges out 

3. To an observer on the earth the stars appear to 

twinkle. This can be ascribed to 

(a) 

(b) 

[CPMT; AFMC] 

The fact that stars do not emit light 

continuously 

Frequent absorption of star light by their 

own atmosphere 

(c) Frequent absorption of star light by the 

earth’s atmosphere 

(d) The refractive index fluctuations in the 

earth’s stmosphere 

4. A cut diamond sparkles because of its 

(a) Hardness 

(b) High refractive index 

(c) Emission of light by the diamond 

(d) Absorption of light by the diamond 

[NCERT] 

5. The angle of the prism is 6º and its refractive 

index for green light is 1.5. When a green ray 

passes through it, its deviation will be 

(a) 30º (b) 15º 

(c) 90º (d) 3º 

[CPMT] 

6. When white light passes through a glass 

prism, one gets spectrum on the other side of 

the prism. In the emergent beam, the ray 

which is deviating least is or 

Deviation by a prism is lowest for 

[MP PMT] 

(13)


(a) Violet ray 

(c) Red ray 

(b) Green ray 

(d) Yellow ray 

7. We use flint glass prism to disperse 

polychromatic light because light of different 

colours 

(a) Travel with same speed 

(b) 

(c) 

(d) 

[MP PET] 

Travel with same speed but deviate 

differently due to the shape of the prism 

Have different anisotropic properties 

while travelling through the prism 

Travel with different speeds 

8. The Spectrum of light coming out from a neon 

lamp is 

(a) Continous 

(c) Absorption 

[MP PET / PMT] 

(b) Line 

(d) Band 

9. Which of the following represents an infrared 

wavelength 

(a) 10 -4 Cm 

(c) 10 -6 Cm 

[CPMT; MP PET/PMT] 

(b) 10 -5 Cm 

(d) 10 -7 Cm 

10. Finger prints on a piece of paper may be 

detected by sprinkling fluorescent powder on 

the paper and then looking it into 

(a) Mercury light 

(c) Infrared light 

[MP PET / PMT] 

(b) Sunlight 

(d) Ultraviolet light 

11. A spectrum is formed by a prism of dispersive 

power ‘ω’. If the angle of deviation is ‘δ’, then 

the angular dispersion is 

(a) ω / δ 

(b) δ / ω 

(c) 1 / ωδ (d) ωδ 

12. Dispersive power depends upon 

[MP PMT] 

[Rajasthan PMT] 

(a) The shape of prism 

(b) Material of prism 

(c) Angle of prism 

(d) Height of the prism 

13. The refractive index of a prism for a 

monochromatic wave is √⎺2 and its refracting 

angle is 60º. For minimum deviation, the 

angle of incidence will be 

(a) 30º (b) 45º 

(c) 60º (d) 75º 

[MP PMT; CPMT; MNR] 

14. The black lines in the solar spectrum during 

solar eclipse can be explained by 

(a) Planck’s law 

(c) Boltzmann’s 

15. In dispersion without deviation 

(a) 

(b) 

(c) 

(d) 

[MP PMT] 

(b) Kirchoffs law 

(d) Solar disturbances 

The deviation produced by one is 

crossed by the other prism 

The dispersion produced by one prism 

is crossed by the other prism 

The resultant deviation is zero 

None of the above 

16. A glass prism (m = 1.5) is dipped in water (m 

= 4/3) as shown in figure. A light ray is 

incident normally on the surface AB. It 

reaches the surface BC after totally reflected, 

if 

fig.-24 

[IIT; MP PMT] 

(14)

(a) sin θ > 8/9 (b) 2/3 < sin θ < 8/9 

(c) sin θ < 2 / 3 

(d) It is not possible 

17. Continuous spectrum is not obtained 

(a) By sun as seen from earth 

(b) By red hot solid 

(c) Fluorescent solid 

(d) Sparks in the air 

18. What will be the angle of glass prism which 

has no emergent ray, while critical angle is C 

(a) Equal to 2C 

(c) More than 2C 

(b) Less than 2C 

(d) None of the above 

19. A thin oil layer floats on water. A ray of light 

making an angle of incidence of 40º shines on 

oil layer. The angle of refraction of light ray 

with water surface is 

(a) 36.1º (b) 44.5º 

(c) 26.8º (d) 28.9º 

(µ oil = 1.45,µ water = 1.33) 

[MP PMT] 

20. The wavelength of light visible ot eye is of the 

order of 

(a) 10 -2 m (b) 10 -10 

(c) 1 m 

(d) 6 x 10 -7 m 

[CPMT] 

21. Light rays from a source are incident on a 

glass prism of index of refraction m and angle 

of prism a. At near normal incidence, the 

angle of deviation of the emerging rays is 

(a) (µ − 2) α 

(c) (µ + 1) α 

(b) (µ − 1) α 

(d) (µ + 2) α 

[MP PMT] 

22. Signals of danger are made red, because 

(a) Our eye is most sensitive for red colour 

(b) Scattering is minimum for red colour 

(c) Scattering is maximum for red colour 

(d) Red colour is internationally accepted 


(15) 

colour for danger 

23. Our eye is most sensitive for which of the 

followwing wavelength 

(a) 4500 Å 

(b) 5500 Å 

(c) 6500 Å 

(d) Equally sensitive for all wave lengths of 

visible spectrum 

24. The minimum temperature of a body at which 

it emits light is 

(a) 1200º (b) 1000ºC 

(c) 500º (d) 200ºC 

25. A beam of light propagating in medium A 

with index of refraction n (A) passes across 

an interface into medium B with index of 

refraction n (B) . The angle of incidnece is 

grater than the angle of refraction; v (A) and 

v (B) denotes the speed of light in A and B. 

Then which of the following is true? 

(a) v (A) > v (B) and n (A) > n (B) 

(b) v (A) > v (B) and n (A) < n (B) 

(c) v (A) < v (B) and n (A) > n (B) 

(d) v (A) < v (B) and n (A) < n (B) 

[MP PAT] 

26. When a white light passes through a hollow 

prism, then 

[MP PMT] 

(a) There is no dispersion and no deviation 

(b) Dispersion but no deviation 

(c) Deviation but no dispersion 

(d) There is dispersion and deviation both 

27. A thin lens focal length f1 and its aperture has 

diameter d. It forms an image of intensity I. 

Now the central part of the aperture upto 

diameter d is blocked by an opaque paper. 

2 

The focal length and image intensity will


change to 

(a) f 2 and I 2 

(c) 3f 

4 and I 2 

[CPMT; CET; MP PET] 

(b) f and I 4 

(d) f and 3I 

4 

28. The refractive index of glass is 1.5 The 

velocity of light in glass is 

(a) 3 x 10 10 cm/sec 

(b) 4.5 x 10 10 cm/sec 

(c) 2 x 10 10 cm/sec 

(d) 10 10 cm/sec. 

29. Light of wavelength 7200Å in air has a 

wavelength in glass (µ = 1.5) equal to 

(a) 7200 Å 

(c) 10800 Å 

(b) 4800 Å 

(d) 7201.5 Å 

30. A fish rising vertically with speed 2ms-1 to 

the surface of water sees a bird diving 

vertically towards it with speed 9ms -1 ? Given 

a 

µ w = 4 , the actual velocity of dive of the bird 

3 

is 

(a) 6 ms -1 (b) 4 ms -1 

(c) 8.4 ms -1 (d) 4.5 ms -1 

31. It is possible to observe total internal 

reflection when a ray travels from 

(a) Air into water 

(b) Air into glass 

(c) Water into glass 

(d) Glass into water. 

32. Which of the following statements is wrong? 

(a) Light travels faster in vacuum than in air 

(b) 

(c) 

The wavelenght of light is longer than 

the wavelength of sound 

Sound travels nearly 330 meters in one 

second 

(d) Speed of sound is ‘Mach number one’. 

33. A diver in swimming pool wants to signal to 

a person lying on the edge of the pool by 

flashing his water proof flash light. For this 

(a) 

(b) 

(c) 

(d) 

He must direct the beam vertically 

upwards 

He has to direct the beam horizontally 

He has to direct the beam at an angle to 

the vertical which is slightly less than 

the critical angle of incidence for total 

internal reflection 

He has to direct the beam at an angle to 

the vertical which is slighly more than 

the critical angle of incidence for total 

internal reflection. 

34. A glass slab of thickness 4 cm contains the 

same number of waves as 5 cm of water when 

both are traversed by the same 

monochromatic light. If the refractive index 

of water is 4 , what is that of glass? 

3 

(a) 5 3 

(c) 16 

15 

(b) 5 4 

(d) 1.5 

35. A ray of light passes from a denser to a rarer 

medium. At the surface of separation the 

angle of incidence is i and the angle between 

reflected and refracted rays is of 90º. If the 

angle of reflection and refraction are and r’ 

respectively, then the value of the critical 

angle is 

(a) sin -1 (tan r’) (b) sin -1 (tan r) 

(b) sin -1 (tan i) (b) sin -1 (tan i) 

[IIT] 

36. Two parallel light rays are incident at one 

surface of a prism of refractive index 1.5 (see 

(16)

figure). What is the angle between the rays as 

they emerge? 


fig.25 

(a) 19º (b) 37º 

(c) 45º (d) 49º 

37. Two immiscible liquids are in a cylindrical 

vessel of depths of 8.4 cm and 7.8 cm, their 

refractive indices being 1.2 and 1.3 

respectively. 

fig.26 

An object O at the bottom is seen from 

vertically above the liquids. The upward 

dipalcement in cm in its apparant position is 

(a) 13 cm 

(c) 6.8 cm 

(b) 11.4 cm 

(d) 3.2 cm 

38. A prism can produce a minimum deviation 

δm 

fig.27 

in a light beam. If three such prisms are 

combined, as shown the minimum deviation 

that can be produced in this beam is 

(a) 0 

(c) 2δm 

(b) δm 

(d) 3δm 

39. The focal length of a plano convex lens is 20 

cm. Its plane side is silverred. Mark correct 

statement/s 

(a) 

(b) 

An object placed at 15 cm on the axis 

with the convex side gives rise to an 

image at a distance of 30 cm from it. 

An object placed at 20 cm on the axis on 

the convex side gives rise to an image at 

a distance of 40 cm from it. 

(c) It acts as a convex mirror. 

(d) It acts as a concave mirror. 

40. The refractive indices of violet and red light 

are 1.54 and 1.52 respectively. If the angle of 

prism is 10º, the angular dispersion is 

(a) 0.02 (b) 0.2 

(c) 3.06 (d) 30.6 

[PMT MP] 

41. In a thin prism of glass ( a µ g = 1.5) which of 

the following relations between the angle of 

minimum deviation D m and angle of 

refraction r will be correct 

(a) D m = r 

(b) D m = 1.5 r 

[PMT MP] 

(17)

(c) D m = 2r (d) D m = r 2 

42. A ray falls on a prism ABC (AB = BC) and 

travels as shown. The minimum refractive 

index of the prism material should be 

(a) 4 3 

(c) 1.5 

fig.28 

(b) √⎺2 

(d) √⎺3 

43. If there were no atmosphere, then the duration 

of day on the earth will 

(a) decrease 

(b) increase 

(c) remain the same 

(d) depend upon the weather. 

44. A man stands by lake and sees a fish. He tries 

to hit the fish with a stone but misses. To 

succeed he shoud have 

(a) aimed above the fish 

(b) aimed below the fish 

(c) aimed to the right or left of the fish 

(d) alloed for the deflectin of the stone by 

the water. 

45. A pile driven into the bottom of a lake extends 

3 metre above the bottom of a lake and 1 metre 

above the surface of water aµw = 4 . If the sun 

3 

is 30º above the horizon, then the length of the 

shadow of the pile on the bottom of the lake 

is approximately 


(18) 

(a) 1.73 metres 

(c) 3.00 metres 

(b) 2.73 metres 

(d) 3.46 metres 

46. A small air bubble is situated in a cube of 24 

cm edge. When viewed from one face it 

apears to be 10 cm from the surface, and 

through the opposite face 6 cm from the 

surface. Then the refractive index of the 

material of the cube is 

(a) 1.2 (b) 1.4 

(c) 1.5 (d) 1.6 

[BHU] 

47. The refractive index of a glass prism depends 

upon 

(a) The angle of prism 

(b) The angle through which it deviates an 

(c) 

(d) 

incident beam of light 

The colour of the incident light 

the intensity of incident light 

48. A crow is perched on a tree at point X. Food 

grains are scattered between A and B. Where 

fig.29 

must the crow pech the grain if it wants to go 

to z after perching, covering the least distance 

during its flight. 

(a) At a point where i > r 

(b) At a point where i = r 

(c) At a point where i < r 

(d) none of the above 

49. When light passes from one medium to 

another, the characteristic, that remains 

constant, is : 

(a) Velocity 

(b) Wavelength


(c) Amplitude 

(d) Frequency 

50. Light passes from air into a liquid. The angle 

of incidence is 60º. The deviation produced is 

15º. The refractive index of the liquid is : 

(a) 1.5 (b) 1.33 

(c) 1.22 (d) 1.63 

51. When a glass slab is placed on a cross made 

on a sheet, the cross apperas rased by 1 cm. 

The thickness of the glass is 3 cm. The critical 

angle for glass is : 

(a) sin -1 (0.33) (b) sin -1 (0.5) 

(c) sin -1 (0.66) (d) sin -1 (√⎺3 ⁄ 2) 

52. A ray of light from a denser medium strikes a 

rarer medium at an angle of incidence i. The 

reflected and refracted rays make an anlge of 

90º with each other. The angles of reflection 

and refraction are r & r’. The critical angle is 

: 

(a) sin -1 (tan r) (b) sin -1 (tan i) 

54. A white ray of light is passing through a 

parallel glass slab. The emergent ray : 

(a) Undergoes dispersion only 

(b) Undergoes deviation only 

(c) Undergoes both dispersion and 

deviation 

55. It is possible to observe total interanl 

reflection when a ray travels from : 

(a) Air into water 

(b) Air into glass 

(c) Its frequency devreases 

(d) Its wavelength decreases 

56. Immiscible transparent liquids A, B, C, D and 

E are placed in a rectangular container of glass 

with the liquids making layers according to 

their densities. The refractive index of the 

liquids are shown in the adjoining diagram. 

fig.30 

(c) sin -1 (tan r’) (d) tan -1 (tan i’) 

53. Which one of the following represents 

correctly the variation of angle of deviation 

(δ) with angle of incidence (i) for refraction 

at a prism? 

fig.31 

(19) 

fig.32 

The container is illuminated from the side and 

a small piece of glass having refractive index 

1.61 is gently dropped into the liquid layers. 

The glass piece, as it descends downwards, 

will not be visible in : 

57. Refractive index is : 

(a) 

(b) 

(c) 

Directly proportional to wavelength of 

light 

Inversely propottional to wavelength of 

light 

Inversely proportional to square of


(d) 

wavelength of light 

Directrlly proportional to the square of 


58. For a prism PQR, the incident and emergent 

rays are parallel as shown in Fig. The 

minimum value of refractive index of the 

prism is : 

61. P is a small angled prism of angle 3º made of 

a material of refractive index 1.5. A ray of 

light is incident as shown in Fig.34 M is a 

plane 

(a) 1.5 

fig.33 

(b) √⎺2 

(c) √⎺3 (d) 2 

59. A vessel of depth 2d cm is half filled with a 

liquid of refractive index µ 1 and the upper half 

with a liquid of refractive index µ 2. The 

apparent depth of the vessel seen 

perpendiculary is : 

(a) d ⎛ ⎜ 

⎝ 

µ 1 µ 2 

µ 1 + µ 2 

⎞ 

⎟⎠ (b) d ⎛ ⎜ 

⎝ 

1 

µ 1 

+ 1 µ 2 

⎞ 

⎟⎠ 

(c) 2d ⎛ ⎜ 

⎝ 

1 

µ 1 

+ 1 µ 2 

⎞ 

⎟⎠ (d) 2d ⎛ ⎜ 

⎝ 

1 

µ 1 µ 2 

⎞ 

⎟⎠ 

60. In a room, artificial rain is produced at one end 

and a strong source of white light is switched 

on at the other end. To observe the rainbow an 

observer must : 

(a) Look any where in the room 

(b) Look towards the source 

(c) Look towards raindrops 

(d) Look in a direction equallly inclined to 

the source of raindrops 

(20) 

fig.34 

mirror. The angle of deviation for the ray 

reflected from the mirror M with respect to the 

inceidnt ray is : 

(a) 4.5º (b0 175.3º 

(c)177º (d) 178.5º 

62. A fish is a little away below the surface of a 

lake. If the critical angle is 49º, then the fish 

could see things above the water surface 

within an angular range of θ ο where : 

fig.35 

(a) θ = 49º (b) θ = 90º 

(c) θ = 98º (d) θ = 24 1 2 º 

63. A thin prism P 1 with angle 4º and made from 

glass of refractive index 1.54 is combined 

with another thin prism P 2 made from glass of 

refractive index 1.72 to produce dispersion

without deviation. The angle of the prism P 2 

is: 

(a) 5.33º (b) 4º 

(c) 3º (d) 2.6º 

[IIT JEE] 

64. If sun is shining brightly in one part of the sky 

after rain, how many rainbows are usually 

observed? 

(a) One 

(c) Four 

(b) Two 

(d) Infinite 

65. In vacuum the speed of light depends upon : 

(a) The wavelentth 

(b) The frequency 

(c) The intensity of light 

(d) None of these 

66. Velocity of light in water, glass and vacuum 

have the values V w, V g and V c respectively. 

Which of the following relations is true? 

(a) v w = v g = v c 

(b) v w > v g but v w < v c 

(c) v w = v g but v w < v c 

(d) v c = v g but v w < v g 

67. Just before the time of sunset the sun appears 

to be red because : 

(a) The sun changes its shape at that time 

(b) 

Of the scattering of light 

(c) Of the effects of refration 

(d) Of the effects of diffraction 

68. If the critical angle for total internal reflection 

from a medium to vacuum is 30º, the velocity 

of light in the medium, is : 

(a) 3 x 10 8 m/s 

(b) 1.5 x 10 8 m/s 

(c) 6 x 10 8 m/s 

(d) √⎺3 × 10 8 m/s 

69. When the moon is near the horizon, it appears 


(21) 

bigger. This is due to : 

(a) Atmospheric refraction 

(b) Scattering of light 

(c) Diffraction 

(d) Optical illusion 

70. A microscope is focussed on a mark. Then a 

glass slab of refractive index 1.5 and 

thickness 6 cm is placed on the mark. To get 

the mark again in focus, the microscope 

should be moved : 

(a) 2 cm downward 

(b) 2 cm upward 

(c) 4 cm upward 

(d) 9 cm upward 

71. Which of the following statements is wrong? 

(a) Light travels faster in vacuum than air : 

(b) 

(c) 

(d) 

The wavelength of light is longer than 

the wavelength of sound 

Sound travels nearly 330 metres in one 

second 

Speed of sound is ‘Mach number one’ 

72. The refractive index of a material of a prism 

of angles 45º – 45º – 90º is 1.5. The path of 

the ray of light incident normally on the 

hypotenuse side is shown in : 

fig.36 

73. Refractive index is the highest for : 

(a) Glass 

(b) Water 

[EAMCET]


(c) Rock-salt 

(d) Diamond 

74. The astronaut in a space ship sees the sky 

away from the sun as : 

(a) Red 

(c) White 

(b) Black 

(d) Blue 

75. The velocity of light in glass, whose refractive 

index with respect to air is 1.5, is 2 x 10 8 

m/sec. In a certain liquid the velocity of light 

is found to be 2.5 x 10 8 m/sec. The refractive 

index of the liquid with respect to air is : 

(a) 0.64 (b) 0.80 

(c) 1.20 (d) 1.44 

76. Refractive index varies : 

(a) 

(b) 

(c) 

(d) 

Directly as the wavelength of light 

Inversely as the wavelength of light 

Inversely as the square of wavelength of 

light 

Inversely as the fourth power of the 


77. If ∈ ο and µ are respectively, the electric per 

mittivity and the magnetic permeability of 

free space, ∈ and µ the corresponding 

quantities in a medium, the refractive index of 

the medium is : 

⎛ µ∈ 

(a) √⎺⎺⎺⎺ 

⎞ 

⎜ 

⎝ 

µ o ∈ ⎟⎠ (b) µ∈ 

ο µ o ∈ ο 

⎛µ (c) √⎺⎺⎺⎺ 

o ∈ ο ⎞ 

⎛ µµ 

⎜ ⎟ (d) √⎺⎺⎺⎺ 

o ⎞ 

⎜ ⎟⎠ 

⎝ µ∈ ⎠ 

⎝∈∈ ο 

78. The angle of a prism is A and that of minimum 

deveiation is (180º – 2 A). Then the refractive 

index of the material of the prism is : 

(a) sin (A/2) 

(b) cos (A/2) 

(c) tan (A/2) (d) cot A/2 

79. A beam of monochromatic blue light of 

wavelength 4200Å in air travels in water 

(refractive index, µ = 4/3). Its wavelength in 

water will be : 

(a) 2800 Å 

(c) 3150 Å 

(b) 5600Å 

(d) 4000 Å 

[MNR] 

80. The phenomenon of total internal reflection 

does not play any role in the : 

(a) Formation of rainbow 

(b) Sparkling of diamond 

(c) Phenomenon of mirage 

(d) None of the above 

81. A beam of white light is incident on a hoolw 

prism of glass. Then : 

fig.37 

(a) The light emerging from prism gives no 

(b) 

spectrum 

The light emerging from prism gives 

spectrum but the bednding of all colours 

is away from base 

(c) The light emerging from prism gives 

(d) 

spectrum, all the colours bend towards 

base, the violet most and red the least 

The light emerging from prism gives 

spectrum, all the colours bend towards 

base, the violet the least and red the most 

82. When a ray is refracted from one medium into 

another medium, the wavelength changes 

from 6000 Å to 4000 Å. The critical angle for 

a ray from second medium will be : 

[CPMT] 

(22)


(a) cos −1 ⎛ 2⎞ 

⎜ ⎝ 

3⎟ 

(b) sin −1 ⎛ 2⎞ 

⎜ 

⎠ 

⎝ 

3⎟ 

⎠ 

(c) tan −1 ⎛ 3⎞ 

⎜ ⎝ 

2⎟ 

(d) sin −1 ⎛ 2 ⎞ 

⎜ 

⎠ 

⎝ 

√⎺ ⎺13 ⎟ 

⎠ 

83. The Tyndall effect is– 

(a) 

(b) 

(c) 

(d) 

The scattering of light by the particles 

of smoke and dust present in the 

atmosphere. 

The refraction of light from denser to 

rarer medium 

The total internal refraction of light 

The rectilinear propagtion of light 

84. Which of the following waves can not be 

polarized? 

(a) Sound wave 

(c) Radio wave 

(b) light wave 

85. The unit of refractive index is– 

(a) m/s 

(c) cm 

(d) all of above 

(b) m 

(d) unitless 

86. Perfectly transparent material will not be 

visible in vacuum if its refractive index is 

(a) one 

(c) more than one (d) 1.33 

(b) less them one 

87. A pencil dipped partially into water appears 

bent because of. 

(a) reflection at water surface 

(b) diffraction at water surface 

(c) refraction at water surface 

(d) water is flowing 

88. If a hollow prism with refracting angle of 60º 

is filled with such a liquid which produces 

minimum deviation of 30º, then the refractive 

index of the prism will be– 

(a) 1.7 (b) 2.4 

(c) 1.41 (d) 1.59 

89. The velocity of light in diamond, glass and 

water decreases in the following order. 

(a) diamond > glass > water 

(b) diamond < glass < water 

(c) water > glass > dismond 

(d) diamond > water > glass 

90. The phenomenon of dispersion is observed in. 

(a) only longitudinal waves 

(b) only transverse waves 

(c) in both 

(d) none of two 

91. The human eye is most sensitive for the wafe 

length. 

(a) 5500Å 

(c) 6500Å 

(b) 4500Å 

(d) 8000Å 

92. A ray of light is incident on a glass slab of 

refractive index 1.52. If the reflected and 

refracted rays of light are mutually 

perspendicular to each other then the angle of 

incidence will be 

(a) 90º (b) 60º 

(c) 56º40’ (d) 19º58’ 

93. The cause of mirage in desert areas is- 

(a) The refractive index of atmosphere 

(b) 

(c) 

(d) 

decrease with height. 

The refractive index of atmosphere 

increases with height. 

The refractive index of atmosphere does 

not change with height. 

Scattering. 

94. When a ray of light enters from one medium 

to another then its velocity in second medium 

becomes double. The maximum value of 

angle of incidence so that total interanl 

reflection may not take place will be 

(a) 60º (b) 180º 

(c) 90º (d) 30º 

(23)

95. Out of the following, whose velocity is equal 

to that of light? 

(a) of β-rays 

(b) of sound waves 

(c) of ultrasonic waves 

(d) of thermal waves 

96. The hours in a clock are marked by points. 

When it is put in front of a mirror and looked 

into the mirror then time noted is 8.20 The 

correct time is - 

(a) 4 : 40 (b) 8 : 20 

(c) 2 : 40 (d) 3 : 40 

97. The correct curve between refractive index n 

(a) A 

(c) B 

and wavelength λ will befig.38 

(b) D 

(d) C 

98. If the velocity of light in glass is 2 x 10 8 m/s 

then its velocity in water will be if n g = 1.5 and 

n ω = 4/3 

(a) 3 x 10 8 m/s (b) 2.66 x 10 8 m/s 

(c) 1.5 x 10 5 m/s 

(d) 2.25 x 10 8 m/s 

99. The angle of minimum deveiation by a prism 

(µ = 1.5) of angle 25º when placed in air is 

10º. The angle of minimum deviation, when 

the prism is placed in aliquid of refractive 

index 4 will be– 

3 

(a) 1.25º (b) 2.5º 


(24) 

(c) 3.75º (d) 5º 

100. The angle of dispersion of a spectrum 

obtained by aprism of angle 60º is 12º. The 

difference of refractive indices for these rays 

will be– 

(a) 0.4 (b) 0.3 

(c) 0.2 (d) 0.1 

101. A ray of light is incident normally on one face 

of a right angled isosceles prism. It is total 

internally reflected at another face. The 

minimum value of the refractive index of the 

material of the prism will be– 

(a) √⎺ ⎺10 

(c) √⎺3 

(b) √⎺5 

(d) √⎺2 

102. The radii of curvature of the two surfaces of 

a lens are 20 cm and 30 cm and the refractive 

index of the material of the lens is 1.5 If the 

lens is concavo-convex then focal length of 

the lens is : 

(a) 24 cm 

(c) 15 cm 

(b) 10 cm 

(d) 120 cm 

103. The minimum distance between an object and 

its real image formed by a convex lens is : 

(a) 1.5 f 

(c) 2.5 f 

(b) 2f 

(d) 4f 

104. A concave and a convex lens have the same 

focal length of 20 cm., and are put into contact 

to form a lens combination. The combination 

is used to view an object of 5 cm length kept 

at 20 cm from the lens combination. As 

compared to the object, the image will be : 

(a) Magnified and inverted 

(b) Rduced and erect 

[CPMT] 

(c) Of the same size as the object and erect 

(d) Of the same size as the object but 

inverted


105. When a thin convex lens is put in contact with 

a thin concave lens of the same focal length, 

the resultant combination has a focal length 

equal to : 

(a) f/2 

(c) 0 

(b) 2f 

(d) ∞ 

106. If the space between the lenses in the lens 

combination shown were filled with water, 

what sould happen to the focal length and 

power of the lens combination? 

Focal length 

(a) Decreased 

(b) Decreased 

(c) Increased 

(d) Increased 

fig.39 

Power 

increased 

unchanged 

unchanged 

decreased 

107. If the behaviour of light rays through a convex 

looking lens is as shown in the following 

figure, then : 

glass lens appears to be 2 cm when observed 

normally through the plane face, and when 

observation is taken through the curved face 

the greatest thickness appears to be 20/9 cms. 

If real thickness is 3 cm then the refractive 

index of glass is : 

(a) 1.35 (b) 1.50 

(c) 1.11 (d) 1.20 

109. A lens of power + 2 dioptres is placed in 

contact with a lens of pwoer - 1 dioptre. The 

combination will behave like : 

[MNR] 

(a) A divergent lens of focal length 50 cm 

(b) 

(c) 

Convergent lens of focal length 50 cm 

A divergent lens of focal length 100 cm 

(d) A convergent lens of focal length 100 

cm 

110. An equiconvex lens is made from glass of 

refractive index 1.5. If the radius of each 

surface is changed from 5 cm to 6 cm then the 

power : 

(a) Remains unchanged 

(b) 

Increases by 3.33 dioptre approx. 

(c) Decrease by 3.33 dioptre approximately 

(d) 

Decreases by 5.5 dioptre approximately 

111. A glass concave lens is placed in a liquid in 

which it behaves like a convergent lens. If the 

refractive indices of glass and liquid be aµg 

and aµl respectively, then : 

(a) aµ g = aµ l 

(b) aµ g < aµ l 

fig.40 

(a) µ = µ 2 (b) µ < µ 2 

(c) µ > µ 2 (d) µ < µ 2 

108. The greatest thickness of a plano-convex 

(25) 

(c) aµ g > aµ l 

(d) aµ g > 3 aµ l 

112. Two thin lenses, one of focal length + 60 cm 

and the other of focal length –20 cm are put 

in contact. The combined focal length is : 

(a) + 15 cm 

(b) – 15 cm 

[CPMT]


(c) + 30 cm 

(d) – 30 cm 

113. Given aµ g = 3/2 and aµ w = 4/3. An equi-convex 

lens with radius of each surface equal to 20 

cms is placed in air. Then its focal lenght is : 

(a) 20 cms 

(c) 40 cms 

(b) 30 cms 

(d) 80 cms 

114. A lens is made of amaterial of refractive indes 

µ 2. It is immersed in a medium of refractive 

index µ 1. If R 1 and R 2 are the radii of curvature 

of the lens surfaces; the focal length f is : 

(a) 1 f = (µ − 1) ⎛ ⎜ ⎝ 

1 

R 1 

− 1 R 2 

⎞ ⎟⎠ 

(b) 1 f = ⎛ ⎜ 

⎝ 

µ 2 

µ 1 

− 1 ⎞ ⎟ 

⎠ 

⎛ ⎜⎝ 

1 

R 1 

− 1 R 2 

⎞ ⎟⎠ 

(c) 1 f = ⎛ ⎜ 

⎝ 

µ 2 

µ 1 

− 1 ⎞ ⎟ 

⎠ 

⎛ ⎜⎝ 

1 

R 1 

+ 1 R 2 

⎞ ⎟⎠ 

(d) 1 f = ⎛ ⎜ 

⎝ 

µ 1 

µ 2 

− 1 ⎞ ⎟ 

⎠ 

⎛ ⎜⎝ 

1 

R 1 

+ 1 R 2 

⎞ ⎟⎠ 

115. In a film projector a convex lens is usually 

placed between the bulb and the film. The 

purpose of this lens is to : 

(a) Make the image brighter 

(b) Laterally invert the image 

(c) Produce an image of the film on the 

screen 

(d) Correct any distortions in the image 

116. A double convex air bubble in water would 

behave as a : 

(a) Divergent lens 

(c) Concave mirror 

(b) Convergent lens 

(d) Plane mirror 

117. The curved face of a plano-convex lens has a 

radius of curvature of 250 mm. The refractive 

index of lens material is 1.5. The power of the 

lens is : 

(a) 0.2 D 

(c) + 2 D 

(b) - 0.2 D 

(d) - 2 D 

118. A lens of focal length f is placed in air. The 

relation between the object and image 

position is : 

(a) 1 v + 1 u = 1 f 

(c) 1 u – 1 v = 1 f 

(b) 1 v – 1 u = 1 f 

(d) 1 v + 1 u = 2 R 

119. An object is placed at a point distant x from 

the focus of a convex lens and its image is 

formed at I as shown in the figure. The 

distances x, x’ satisfy the relation : 

(a) x + x’ 

2 

(c) x + x’ = 2f 

fig.41 

= f (b) f 2 = xx’ 

(d) x – x’ 2f 

120. A convergent beam is incident on a convex 

lens L as shwon in fig.42 The image formed 

is : 

fig.42 

(a) Real, erect and enlarged 

(b) Real, erect and diminished 

(c) Virtual, erect and diminished 

(d) Virtual, erect and enlarged 

121. A convergent beam is incident on a concave 

lens as shown in Fig. Which of the following 

statements is not correct : 

(26)

fig.43 

(a) The image formed is real 

(b) The image formed is virtual 

(c) The image formed is erect 

(d) The image formed is magnified 

122. A spherical convex surface separates object 

and image space of refractive index 1.0 and 

1.33. If radius of curvature of the surface is 

0.1 m, its power is : 

(a) 2.48 D 

(c) 3.3 D 

(b) – 2.48 D 

(d) – 3.3 D 

123. A thin lens has focal length f and its aperture 

has diameter d. It forms an image of intensity 

I. Now the central part of the aperture upto 

diametter d/2 is blocked by an opaque paper. 

The focal length and the image intensity will 

change to : 

(a) f/2 and I/2 (b) f and I/4 

(c) 3f/4 and I/2 (d) f and 3 I / 4 

124. Two thin lenses of focal lengths 20 cm and 25 

cm are placed in contact. The effective power 

of the combination is : 

(a) 45 diopters 

(c) 1/9 dioptres 

(b) 9 dioptres 

(d) 6 dioptres 

125. The minimum distance between a real object 

and its virtual image formed by a convex lens 

is : 

(a) f 

(c) 0 

(b) 4f 

(d) 2f 

126. For a spherical surface separating two media 

of refractive index µ 1 and µ 2, the focal length, 

f, is : 


(27) 

(a) f = R/2 

(b) f = R 

(c) f = (µ 1–µ 2 )/µ 2 R (d) µ 2R/ (µ 2 –µ 1) 

127. Two thin lenses of focal lengths f1 and f2 are 

in contact and coaxial. The combination is 

equivalent to a single lens of power : 

(a) 

f 1 f 2 

f 1 + f 2 

(b) 1 2 (f 1 + f 2 ) 

(c) f 1 + f 2 

f 1 f 2 

(d) √⎺⎺(f 1 f 2 ) 

128. The radii of curvature of the two surfaces of 

lens shown in fig. are 100 cm and 80 cm 

respectively. The lens is immersed competely 

fig.44 

in a liquid (m = 1.25). The focal length of the 

lens is : 

(a) 0.25 m 

(c) –2.8 m 

(b) 25 m 

(d) – 2.8 cm 

129. An equi-convex lens is cut into two halves by 

a plane AB as shwon in Fig. The focal length 

of each half so obtained is : 

fig.45 

(a) f (b) f/2 

(c) 2f (d) 3f/2 

130. A convex surface of radius of curvature R

separates two media of refractive index µ 1 and 

µ 2. An object is placed in the medium of 

refractive index µ 1. The relation between the 

object and image position is : 

(a) 1 v − 1 u = µ − 1 

R 

(b) µ 2 

v − µ 1 

u = µ 2 − µ 1 

R 

(c) µ 2 

v + µ 1 

u = µ 2 − µ 1 

R 

(d) µ 2 

v − µ 1 

u = µ 1 − µ 2 

R 

131. Following Fig. shows three arrangements of 

lenses. The radii of curvature of all the curved 

surfaces are same. The ratio of the equivalent 

focal length of combination P, Q and R is : 

fig.46 

(a) 1 : 1 : 1 (b) 1 : 1 : – 1 

(c) 2 : 1 : 1 (d) 2 : 1 : 2 

132. For a sphereical surface of radius of curvature 

R, separating two media of refractive index 

µ 1 and µ 2, the two principal focal lengths are 

f1 and f2 fespectively. Which one of the 

following relations is correct? 

(a) f 1 = f 2 (b) f 2/µ2 = f 1/µ 1 

(c) f 2/µ 2 = –f1/µ1 (d) f2/µ1 = f 1/µ 2 

133. The focal length of convex lens is f. An object 

is placed at a distance x from its first focal 

point. The ratio of the size of the real image 

to that of the object is : 


(28) 

(a) f ⁄ x 2 

(c) f / x 

(b) x 2 ⁄ f 

(d) x / f 

134. An aerolane is flying at a height 1500 m. It 

has a camera having convex lens of focal 

length 45 cm and photographic plate 30 x 30 

cm. How much area on the ground can be 

photographed at one time? 

(a) 10 3 m 2 (b) 10 5 m 2 

(c) 10 4 m 2 (d) 10 6 m 2 

135. If f1 and f2 represent the first and the second 

focal lengths of a single spherical refracting 

surface, then : 

(a) f 2 = –f 1 (b) f 2 = –µf 1 

(c) f 1 = –µf 2 (d) f 1 f 2 = –1 

136. Two lenses of powers 6 D and – 5 D are in 

contact. The focal length of the combination 

is : 

(a) 100/11 cms (b) 16.67 cms 

(c) 100 cms 

(d) 20 cms 

137. A concave lens made of water (µ = 1.33) is 

placed inside a glass slab (µ = 1.5) for an 

object placed within the focus and twice the 

focus, the image formed is : 

(a) Virtual 

(b) Real, inverted and magnified 

(c) Virtual, inverted and magnified 

(d) Real, imverted and diminished 

138. Two thin convex lenses of focal lenghts f1 and 

f2 are placed at a distance d between them. 

For the power of the combination to be zero, 

the separation d is : 

(a) f 1 − f 2 (b) f + f 2 

(c) f 1 ⁄ f 2 (d) √⎺⎺(f 1 f 2 ) 

139. A virtual object between the optical centre 

and the focus of a concave lens produces : 

(a) A real and erect image


(b) A real and inverted image 

(c) A virtual and erect image 

(d) A virtual and inverted image 

140. A luminours object and a screen are fixed at 

a distance D apart. A convex lens of focal 

length f forms a real image on the screen for 

two different positions of the lens that are 

separated by d. Then the ratio of the two 

image sizes for these two positions is : 

(a) D + d 

D − d 

⎛ D + d 

(c) √⎺⎺⎺⎺⎺ 

(b) 

(D + d)2 

(D − d) 2 

⎞ 

⎜ 

⎝(D − d) 

⎟ (d) D d 

⎠ 

141. Three convex lens of focal length 0.1 m each 

are mounted coaxialy, as shown in Fig. An 

lens and the position of the image a thin 

concave lens is introduced. The image formed 

now is at a distance of 5 cm away from the 

earlier position. The focal length of concave 

lens is : 

(a) – 2.5 cm 

(c) – 10 cm 

(b) – 5 cm 

(d) – 30 cm 

144. A convex lens is placed over a plane mirror 

as shown, in Fig. When a pin P is placed as 

fig.47 

object 0 is placed at a distance of 0.2 m from 

L1 and the final image formed is at a distance 

of 0.2 m from L 3. Distance L 1L 2 is : 

(a) 0.2 m 

(c) 0.4 m 

(b) 0.3 m 

(d) 0.1 m 

142. m1 and m2 denote the magnification 

produced by a convex lens on a screen of an 

object when lens is moved in between the 

screen and object are not disturbed at all. Then 

: 

(a) (m 1 ⁄ m 2 ) = 1 (b) m 1 × m 2 = 1 

(c) m 1 

2 

⁄ m 2 = 1 (d) (m 1 

2 

⁄ m 2 2 ) = 1 

143. A convex lens of focal length 10 cm forms a 

real image of an object placed at a distance of 

20 cm from it. Mid-way between the convex 

(29) 

fig.48 

Shown the image formed coincides with the 

pin itself. The focal length of lens is : 

(a) 0.5 m 

(c) 1 m 

(b) 0.25 m 

(d) 2 m 

145. In Question Number 144 if a drop if a drop of 

water is placed between the lens and mirror 

and again image formed is to coincide with 

the pin itself, the position of the pin is : 

(a) Reamains unchanged 

(b) Must be lowered 

(c) Must be raised up 

(d) May be raised up or lowered 

146. A convex lens of power + 6 dioptre is placed 

in contact with a concave with a concave lens 

of power –4 dioptre. What will be the nature 

and focal length of this combination ? 

(a) Concave, 25 cm 

(c) Concave, 20 cm 

[MNR] 

(b) Convex, 50 cm 

(d) Convex, 100 cm 

147. An object 15 cm high is placed 10 cm from


the optical cenre of a thin lens. Its image is 

formed 25 cm from the optical centre on the 

same side of the lens as the object. The height 

of the image is : 

(a) 2.5 cm 

(c) 16.7 cm 

(b)0.2 cm 

(d) 37.5 cm 

[MP PET] 

148. Minimum deviation is observed with a prism 

having angle of prism = 60º, angle of 

deviation = 30º, angle of incidence = i and 

angle of emergence = e. We have 

(a) i = 45º, e = 30º (b) i = 30º, e = 45º 

(c) i = 45º, e = 45º (d) i = 30º, e = 30º 

149. Deviation of 5º is observed from a prism 

whose angle is small and whose refractive 

index is 1.5. The angle of prism is 

(a) 7.5º (b) 10º 

(c) 5º (d) 3.3º 

[MP PET] 

150. The refractive indices of violet and red light 

are 1.54 and 1.52 respectively. If the angle of 

prism is 10º, then the angular dispersion is 

(a) 0.02 (b) 0.2 

(c) 3.06 (d) 30.6 

[MP PMT] 

151. A simple magnifying lens is used in such a 

way that an image is formed at 25 cm away 

from the eye. In order to have 10 times 

magnification, the focal length of the lens 

should be 

(a) 5 cm 

(c) 25 mm 

(b) 2 cm 

(d) 0.1 mm 

[MP PET] 

152. A convex lens A of focal length 20 cm and a 

concave lens B of focal length 5 cm are kept 

along the same axis with the distance d 

between them. If a parallel beam of light 

falling on A leaves B as a parallel beam, then 

distance d in cm will be 

(a) 25 (b) 15 

(c) 30 (d) 50 

[MNR 1990; IIT] 

153. If the refractive indices of a prism for red, 

yellow and violet colours be 1.61, 1.63 and 

1.65 respectively, then the dispersive power 

of the prisms will be 

(a) 

(c) 

1.65 – 1.62 

1.61 − 1 

1.65 − 1.61 

1.63 − 1 

(b) 

(d) 

1.62 – 1.61 

1.65 − 1 

1.65 − 1.63 

1.61 − 1 

[MP PET] 

154. At what angle does the diver in water see the 

setting sun, when the refractive index of water 

is 1.33? 

(a) 0º (b) 41º 

(c) 90º (d) 60º 

[MP PET] 

155. For a material, the refractive indices for 

redviolet and yellow colour light are 

respectively 1.52, 1.64 and 1.60. The 

dispersive power of the material is 

(a) 2 (b) 0.45 

(c) 0.2 (b) 0.045 

156. For a reading lens, we require 

(a) Short focus concave lens 

(b) Long focus concave lens 

(c) Short focus convex lens 

(d) Long focus convex lens 

[MP PMT] 

157. Line spectrum was first of all theoritically 

explained by 

(a) Swan 

(c) Kirchoff 

(b) Fraunhofer 

(d) Bohr 

(30)

158. Immiscible transparent liquids A, B, C, D and 

E are placed in a rectangular container of glass 

with the liquids making layers according to 

their densities. The refractive index of the 

liquids are shown in the adjoingin diagram. 

The container is illuminated from the side and 

a small piece of glass having refractive index 

1.61 is gently dropped into the liquid layer. 

The glass piece as it descends downwards will 

not be visible in 

fig.49 

(a) Liquid A and B only 

(b) Liquid C only 

(c) Liquid D and E only 

(d) Liquid A, B, D and E 

[CPMT] 

159. When an object placed before a convex lens 

between its focal length F and infinity is 

displaced towards 2F, then its image on the 

other side 

[MP Board] 

(a) Moves from 2F towards infinity and 

(b) 

(c) 

increases in size 

Moves from F to 2F and decreases in 

size 

Moves from 2F to F and decreases in 

size 

(d) Moves from F to 2F and increases in 

size 

160. In a thin prism of glass (refractive index 1.5), 

which of the following relations between the 


(31) 

angle of minimum deviations δ m and angle of 

refraction r will be correct? 

(a) δ m = r 

(b) δ m = 1.5 r 

(c) δ m = 2 r (d) δ m = r 2 

161. Visible radiation has wavelength λ 

(a) λ > 8000 Å 

(b) λ millimetre 

(c) λ = 4000 Å to 8000 Å 

(d) λ < 4000 Å 

162. Dispersion can take place for 

[MP PMT] 

[MP PET] 

[MP PET] 

(a) Transverse waves only but not for 

(b) 

(c) 

(d) 

longitudinal waves 

Longitudinal waves only but not for 

transverse waves 

Both transverse and longitudinal waves 

Neither transverse nor longitudinal 

waves 

163. Emission spectrum of CO2 gas 

(a) Is a line spectrum 

(b) Is a band spectrum 

(c) Is a continuous spectrum 

(d) Does not fall in the visible region. 

[MP PET] 

164. When light travels from air to water and from 

water to glass, again from glass to CO2 gas 

and finally through air. The relation between 

their refractive indices will be given by 

(a) an ω x ωn gl x aln gas x gasn a = 1 

(b) an ω x ωn gl x gasn gl x gln a = 1 

(c) an ω x ωn gl x aln gas = 1 

(d) There is no such relation


165. The ray diagram could be correct 

(a) If n 1 = n 2 = n g 

fig.50 

(b) If n 1 = n 2 and n 1 < n g 

(c) If n 1 = n 2 and n 1 > n g 

(d) Under no circumstances 

[CPMT] 

166. A thin convex lens of refractive index 1.5 has 

a focal length of 15 cm in air. When the lens 

is placed in liquid of refractive index 4/3. its 

focal lenght will be 

(a) 15 cm 

(c) 30 cm 

[CPMT; MP PMT] 

(b) 10 cm 

(d) 60 cm 

167. The plane faces of two identical plano-convex 

lenses each having focal length of 40 cms are 

pressed against each other to form a usual 

convex lens. The distance from this lens, at 

which an object must be placed to obtain a 

real, inverted image with magnification one is 

(a) 80 cm 

(c) 20 cm 

[NCERT; CPMT; MP PMT] 

(b) 40 cm 

(d) 162 cm 

168. A double convex lens of focal length 20 cm is 

made of glass of refractive index 3/2 When 

placed completely in water ( a µ ω = 4 ⁄ 3), its 

focal length will be 

(a) 80 cm 

(c) 17.7 cm 

[CBSE; MP PMT/PET] 

(b) 15 cm 

(d) 22.5 cm 

169. Diameter of plano-convex lens is 6 cm and 

thickness at the centre is 3 mm. If the speed 

of light in the material of the lens is 2 x 10 8 

m/sec, the focal lenfth of the lens is 

(a) 15 cm 

(c) 30 cm 

(b) 20 cm 

(d) 10 cm 

[CPMT] 

170. If µ o be the permeability and K o the dielectric 

constant of a medium, its refractive index is 

given by 

1 

(a) 

√⎺⎺µ o K o 

1 

(b) 

µ o K o 

(c) √⎺⎺⎺⎺ µ o K o (d) µ o K o 

[MNR] 

171. A light beam is incident on a rectangular glass 

plate (m = 1.54). The reflected light OB 

passes through a nickol prism. On observing 

the transmitted light while rotating the prism, 

it is seen that 

fig.51 

(a) Intensity of light reduces to zero 

[CPMT] 

(b) Intensity of light decreases and then 

incerases 

(c) There is no change of intensity of light 

(d) 

Intensity of light reduces to zero slowly 

and then start to increase 

172. In the adjoining diagram, a wavefront AB, 

moving in air is incident on a plane glass 

surface XY. Its position CD after refraction 

through a glass slab is shown also along with 

the normals drawn at A and D. The refractive 

(32)


index of glass with respect to air (µ = 1) will 

be equal to 

[CPMT] 

[Manipal MEE] 

(a) sin θ 

sin θ’ 

(c) 

sin φ’ 

sin θ 

fig.52 

(b) sin θ 

sin φ’ 

(d) AB 

CD 

173. For total internal reflection to take place, the 

angle of incidence i and the refractive index 

µ of the medium must satisfy the inequality 

(a) 

1 

sin i < µ (b) 1 

sin i > µ 

(c) sin i < µ (d) sin i > µ 

[MP PET] 

174. A mixture of yellow light of wavelength 5800 

Å and blue light of wavelength 4000 Å is 

incident normally on an air film 0.00029 mm 

thickness. The colour of refrlected light is 

(a) Red 

(c) Violet 

(b) Blue 

(d) Grey 

[AIIMS] 

175. An achromatic combination of lenses is 

formed by joining 

(a) 2 convex lenses 

(b) 2 concave lenses 

(c) 1 convex lens and 1 concave lens 

(d) Convex lens and 1 concave lens 

[BHU] 

176. If the central portion of a convex lens is 

wrapped in black paper as shown in the figure 

(33) 

(a) 

(b) 

(c) 

fig.53 

No image will be formed by the 

remaining portion of the lens 

The full image will be formed but it will 

be less bright 

The central portion of the image will be 

missing 

(d) There will be two images each produced 

by one of the exposed portions of the 

lens 

177. An isosceles prism of angle 120º has a 

refractive indwx of 1.44. Two parallel 

monochromatic rays enter the prism parallel 

to each other in air as shown. The rays 

emerging from the opposite fasces 

fig.54 

(a) Are parallel to each other 

(b) Are divering 

[IIT] 

(c) Make an angle 2 sin -1 (0.72) with each 

other 

(d) Make an angle 2 {sin -1 (0.72) – 30º} 

with each other 

178. A convex lens forms a real image of a point 

object placed on its principal axis. If the upper


2 

half of the lens is painted black, the image will 

(c) 1 [MP PET] 

2 (f 1 +f 2 ) (d) f 1 + f 

f 1 f 2 

(a) f 1 + f 2 

f 1 f 2 

(b) 

f 1 + f 2 

185. With respect to air critical angle in a medium 

(a) Be shifted downwards 

(b) Be shifted upwards 

(c) Not be shifted 

(d) Shift on the principal axis 

181. The distance travelled by light in glass 

(refractive index = 1.5) in a nanosecond will 

be 

[MP PET] 

179. Which of the following diagrams, shows 

(a) 45 cm 

(b) 40 cm 

correctly the dispersion of white light by a 

(c) 30 cm 

(d) 20 cm 

prism 

182. A ray of light of frequency v in air enters into 

[NSEP; MP PET] glass of refractive index m. The correct 

statement is 

[MP PET] 

(a) Frequency of light in glass will change 

(b) Frequency of light and its wavelength 

both in glass will change 

(c) Frequency, wavelength and intensity of 

ligh all will change in glass 

(d) Frequency of light in glass will not 

change 

183. An equiconvex lens of glass of focal length 

0.1 metre is cut along a plane perpendicular 

to principle axis into two equal parts. The ratio 

of focal length of new lenses formed is 

[MP PET] 

(a) 1 : 1 (b) 1 : 2 

(c) 2 : 1 (d) 2 : 1 2 

184. A lens of refractive index n is put in a liquid 

of refractive index n’ of focal length of lens 

in air is f, its focal length in liquid will be 

fig.55 

[MP PET] 

180. Two thin lenses of focal lengths f1 and f2 are 

fn’ (n − 1) f (n’ − n) 

in contact and coaxial. The combination is 

(a) – (b) – 

n’ − n n’ (n − 1) 

equivalent to a single lens of power 

n’ (n − 1) 

[MP PET; MP PMT / PET] 

(c) – (d) fn’n 

f (n’ − n) n − n’ 

(34)


for light of red colour [λ 1] is θ. Other facts 

remaining same, critical angle for light of 

yellow colour [λ 2] will be 

(a) θ 

(c) Less than θ (d) θλ 1 

λ 2 

(b) More than θ 

[MP PET] 

186. With respecting angle of a prism A is small. 

The correct statement for the dispersive 

power of a prism is that dispersive power 

[MP PET] 

(a) Depends upon the material of the prism 

(b) 

(c) 

Dependes upon both material and angle 

of prism 

Depends only upon refracting angle of 

prism 

(d) Is same for all colours of white light 

187. An object of height 1.5 cm is placed on the 

axis of a convex lens of focal length 25 cm. A 

real image is formed at a distance of 75 cm 

from the lens. The size of the image will be 

(a) 4.5 cm 

(c) 0.75 cm 

(b) 3.0 cm 

(d) 0.5 cm 

[MP PET] 

188. A symmetric double convex lens is cut in two 

equal parts by a plane perpendicular to the 

principal axis. If the power of the original lens 

was 4 D, the power of a cut lens will be 

(a) 2 D 

(c) 4 D 

189. Line spectra are due to 

(a) Hot solids 

(b) Atoms in gaseous state 

(b) 3 D 

(d) 5 D 

(c) Molecules in gaseous state 

[MP PMT] 

[EAMCET (Med.)] 

(d) Liquid at low temperature 

190. The phenomenon utilised in an optical fibre is 

(a) Refraction 

(b) Interference 

(c) Polarization 

(d) Total internal reflection 

[CET Karanataka; AMU] 

191. For a medium, refractive indices for violet, 

red and yellow are 1.62, 1.52 and 1.55 

respectively, then dispersive power of 

medium will be 

(a) 0.65 (b) 0.22 

(c) 0.18 (d) 0.02 

[Rajasthan PET] 

192. A 4 cm thick glas plate contains same number 

of waves as contained by 5 cm water column. 

If light is monochromatic and refractive index 

of water is 4/3, then refractive index of glass 

will be 

(a) 5/3 (b) 5/4 

(c) 16/15 (d) 1.5 

[Rajasthan PMT] 

193. The spedd of light in air is 3 x 10 8 m/s. What 

will be its speed in diamond whose refractive 

index is 2.4 

(a) 3 x 10 8 m/s 

(c) 1.25 x 10 8 m/s 

[CET Karantaka] 

(b) 332 m/s 

(d) 7.2 x 10 8 m/s 

194. Which of the following colours suffers 

maximum deviation in a prism 

(a) Yellow 

(c) Green 

(b) Blue 

(d) Orange 

[CET] 

195. A plane glass slab is kept over various 

coloured letters, the letter which appears least 

raised is 

(35)


(a) Blue 

(c) Green 

(b) Violet 

(d) Red 

[BHU] 

196. If the velocity of radio waves is 3 x 10 5 km/s, 

the frequency corresponding to wavelength of 

300 m is 

(a) 10 kHz 

(c) 1kHz 

(b) 1 MHz 

(d) 10 MHz 

[MNR] 

197. An equiconvex glass lens with radius of each 

face as R is placed in air. If a µ g = 3 , the focal 

2 

(a) 4R 

(c) 3 2 R 

(b) 2R 

(d) R 

199. If the lens is immersed in water the focal 

length of the lens is 

(a) 4R 

(c) 3 2 R 

(b) 2R 

(d) R 

200. A double convex thin lens of glass of 

refractive index 1.6 has radii of curvature of 

15 cm each. The focal length of the lens when 

immersed in a fluid of refractive index 1.65 is 

length of the lens is 

(a) 4R 

(c) 3 2 R 

(b) 2R 

(d) R 

198. In the above question if there is water in the 

object space and air in the image space and 

(a) – 247.5 cm 

fig.56 

(b) + 247.5 cm 

given a µ g = 4 , the focal length of the lens 

3 

(c) 125 cm 

(d) 25 cm 

is 

(36)


Answer Sheet 

Q.N. Ans Q.N. Ans Q.N. Ans Q.N. Ans Q.N. Ans Q.N. Ans. 

1 b 

2 b 

3 d 

4 b 

5 d 

6 c 

7 c 

8 b 

9 a 

10 d 

11 d 

12 b 

13 b 

14 b 

15 d 

16 a 

17 b 

18 c 

19 d 

20 d 

21 b 

22 b 

23 b 

24 c 

25 b 

26 a 

27 d 

28 c 

29 b 

30 d 

31 d 

32 b 

33 c 

34 a 

35 b,c 

36 b 

37 d 

38 d 

39 a,d 

40 b 

41 a 

42 b 

43 a 

44 b 

45 d 

46 c 

47 c 

48 b 

49 d 

50 c 

51 c 

52 a,b 

53 d 

54 d 

55 d 

56 b 

57 c 

58 b 

59 b 

60 c 

61 d 

62 c 

63 c 

64 b 

65 d 

66 b 

67 b 

68 b 

69 d 

70 b 

71 b 

72 a 

73 d 

74 b 

75 c 

76 c 

77 a 

78 d 

79 c 

80 d 

81 a 

82 b 

83 a 

84 a 

85 d 

86 a 

87 c 

88 c 

89 c 

90 b 

91 a 

92 c 

93 b 

94 d 

95 d 

96 d 

97 a 

98 d 

99 b 

100 c 

101 d 

102 d 

103 d 

104 c 

105 d 

106 d 

107 b 

108 b 

109 d 

110 c 

111 b 

112 d 

113 a 

114 b 

115 a 

116 a 

117 c 

118 b 

119 b 

120 b 

121 b 

122 a 

123 d 

124 b 

125 c 

126 d 

127 c 

128 a 

129 c 

130 b 

131 a 

132 c 

133 c 

134 d 

135 b 

136 c 

137 b 

138 b 

139 a 

140 b 

141 a,c 

142 b 

143 d 

144 a 

145 c 

146 b 

147 d 

148 c 

149 b 

150 b 

151 c 

152 b 

153 c 

154 b 

155 c 

156 c 

157 d 

158 b 

159 d 

160 a 

161 c 

162 a 

163 b 

164 a 

165 c 

166 d 

167 b 

168 a 

169 c 

170 c 

171 b 

172 b 

173 a 

174 b 

175 c 

176 b 

177 d 

178 c 

179 b 

180 d 

181 d 

182 d 

183 a 

184 a 

185 c 

186 a 

187 b 

188 a 

189 b 

190 d 

191 c 

192 a 

193 c 

194 b 

195 d 

196 b 

197 d 

198 c 

199 a 

200 a 

(37)

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