Light and Optics - Science with Mr. Enns

Light and Optics
Part 1: Properties of Light

Property 1
Light is a form of energy.

Property 2
Light exists as tiny particles called photons.

Property 3
Light travels in straight lines called rays.
Laser
ray

Property 4
Shadows are formed when light rays
are blocked by an object.
Rays of light
Shadow

Property 5
Light travels VERY fast: 300,000 km/s!
This is equal to 670,616,629 mph!
Light can
travel
around
the Earth
8 times in
1 second!

Property 6
Light travels much faster than sound.
Sound travels only 5-7 km/s

Property 7
A luminous object produces its own light.
A non-luminous object only reflects light.

Property 8
When light strikes an object, it can be:
Reflected
Transmitted
Absorbed

Properties of Light – A Summary
1) Light is a form of energy.
2) Light exists as tiny particles called photons.
3) Light travels in straight lines called rays.
4) Shadows form when light rays are blocked.
5) Light travels very fast (300,000 km/s)
6) Light travels faster than sound (5-7 km/s)
7) Luminous objects give off their own light. Nonluminous
objects only reflect light.
8) When light strikes an object, it can be reflected,
transmitted or absorbed.

Any Questions

Light and Optics
Part 2: Reflection, Transmission and Absorption

Review
When light strikes an object, 3 things can happen.
The light can be:
Reflected
Transmitted
Absorbed

Reflection
We see objects because they reflect light into our eyes.

Types Reflection
Light rays reflect differently off of different surfaces.
Clear Reflection
Smooth and shiny
surfaces reflect light
rays at the same angle
e.g. mirrors

Types Reflection
Light rays reflect differently off of different surfaces.
Diffuse Reflection
Rough and dull surfaces
cause light rays to
reflect at different angles
e.g. carpet, wood…

Transmission
Certain objects allow light rays to pass through.
Transparent Objects
Transmit nearly all of the light.

Transmission
Certain objects allow light rays to pass through.
Translucent Objects
Transmit some of the light, but scatters it.

Transmission
Certain objects allow light rays to pass through.
Opaque Objects
Do not transmit any light – they block it.

Absorption
Absorption means to block light rays.
Colored objects appear that way because they
absorb some colors but reflect others.
But first, we must learn
about white light…

White Light
White light is not actually white!
White light is made up of 7 different colors.
We can show this by
shining white light
through a glass prism
The prism splits the
white light into its colors

White Light
The 7 colors in white light make up the spectrum.
Remember: R O Y G. B I V !
Red
Orange
Yellow
Green
Blue
Indigo
Violet

Adding Colors
Colors of light can be combined to make new colors.
The primary colors of light are red, blue & green.
They can combine to produce ALL other colors.
Adding blue and red
makes magenta
Adding blue and
green makes cyan
Adding red and
green makes yellow
Adding all 3
colors makes white

Seeing Color
Lets get back to colored objects…
Different colored objects reflect their own
color of light and absorb all the rest.
Take this red shirt, for example:
It The absorbs shirt looks all the red
since other it colors reflects of red
light the into spectrum our eyes

Seeing Color
A white object reflects ALL seven colors:
Appears
white
A purple object reflects violet, red & blue:
Appears
purple

Seeing Color
If we looked at objects in colored light,
we will see something different.
Consider this red and blue outfit in white light:
White light
Shirt looks red
Shorts look blue

Objects in Colored Light
But in different colored light, this outfit looks different:
Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue

Color Filters
Color filters transmit certain colors and absorb the rest.
White light
Red light
Red filter
White light
Magenta light
Magenta filter

Any Questions

Light and Optics
Part 3: Mirrors and Lenses

Review
When light strikes an object, 3 things can happen.
The light can be:
Reflected
Transmitted
Absorbed

Reflection Off A Plane Mirror
Light reflects off a plane (flat) mirror in a certain way.
Incident Ray Normal Reflected Ray
Angle of
incidence
Angle of
reflection
Plane Mirror

The Law of Reflection
The Law of Reflection states that for a plane mirror:
Angle of Incidence = Angle of Reflection
Incident Ray Normal Reflected Ray
Angle of
incidence
Angle of
incidence
Plane Mirror

Images In A Plane Mirror
Light rays reflect off a plane mirror in a regular way.
Angle of Incidence = Angle of
Reflection
This makes the light rays seem to come from
behind the mirror at an equal distance..
This forms an image that is
upright and the same size.
It is a virtual image, since
the light is not actually
coming from the image.

Forming A Virtual Image
Virtual Image
Upright
Same Size
Reversed

Concave Mirrors
Concave mirrors have surfaces that curve inward.
A concave mirror reflects light rays so that
they converge (meet) at a certain point.
We call this point the
focal point of the mirror.

Concave Mirrors
Concave mirrors form images in 2 different ways.
The type of image depends on the distance
the object is placed from the focal point.
Focal Point

1. Object is placed behind the focal point.
Real Image
Upside down
Smaller
2. Object is placed in front of the focal point.
Virtual Image
Upright
Larger

Convex Mirrors
Convex mirrors have surfaces that curves outward.
A convex mirror reflects light rays
so that they diverge (spread out).
The light rays do NOT
meet at a focal point
in front of the mirror.

Convex Mirrors
Convex mirrors ALWAYS form images the same way.
A convex mirror forms a virtual image
that is smaller than the true object.
Focal Point

Refraction
Refraction is when light rays are bent.
When light rays pass from one material to
another, the light rays refract (bend).
The rays change direction
where the 2 materials meet.
The light bends because it
changes speed in different
materials (mediums).

Refraction
Medium 1 - Air
Light travels fast
Medium 2 - Water
Light travels slow

Index of Refraction
Some mediums refract light rays more than others.
This is described by the index of refraction.

Index of Refraction
Indexes of Refraction for Common Materials
Vacuum 1.00
Air 1.01
Water 1.33
Glycerine 1.47
Glass 1.52
Diamond 2.42

Lenses
A lens is a curved device that refracts light precisely.
Lenses are useful because they can
refract light rays in a predictable way.
There are 2 types of lenses:
Concave
Convex

Concave Lens
A concave lens is thinner in the middle.
A concave lens bends parallel light
rays to make them diverge.
Produce a
virtual image
only

Convex Lens
A convex lens is thicker in the middle.
A convex lens bends parallel light rays
so that they meet at a focal point.
Produce a
real or a
virtual image

Lenses
Lenses have many uses.

Any Questions

Light and Optics
Part 4: The Eye

Eye Anatomy
cornea
lens
sclera
retina
fovea
pupil
iris
optic nerve

Step 1
Light rays pass through the clear cornea,
which focuses them through the pupil.

The Pupil
The size of the pupil can be changed.
This is done by a ring of muscles called
the iris, which surrounds the pupil.
The color of the iris
muscles vary, which
gives people different
eye colors.

Dim Light
Iris muscles contract
Pupil opens - dilates
Lets in more light
Bright Light
Iris muscles relax
Pupil constricts
Lets in less light

SEM – Iris Muscles

Step 2
Light passes through the lens, which further
focuses the rays onto the retina.

The Lens
The thickness of the lens can be changed.
This lens can become thinner or thicker,
depending on how far away an object is.
This is done by
ciliary muscles that pull
the lens from above
and from below.

Distant Objects
Muscles contract
Lens pulled thinner
Focus shifts back
Near Objects
Muscles relax
Lens made thicker
Focus shifts forward

Step 3
The focused light rays hit a layer of lightsensitive
cells found on the retina.

The Retina
The retina is a layer of cells at the
back of the eye that can detect light.
Specialized cells on the retina called
rod and cone cells detect light.
Rods and cones sense
different things about the
light that hits them.
Rod Cell
Cone Cell

Rods and Cones
Cone Cells
At the centre of the retina
3 types: red, green & blue
Detect color
Rod Cells
At the edges of the retina
Only “see” black & white
Detect brightness

The Fovea
The fovea is a dip in the centre of the retina.
Cone cells are concentrated in the fovea:
most color vision occurs here.
Cones concentrated at the fovea

The Fovea
The fovea is a dip in the centre of the retina.
Cone cells are concentrated in the fovea:
most color vision occurs here.
Rods found
at the
edges
Cones concentrated at the fovea

From Eye To Brain
Your brain “sees” differently than your eye.
The optic nerve from the
left eye connects to the
right side of the brain,
and vice versa.
So, your brain sees
everything reversed and
then switches it again!

Summary
1. Light enters the eye through the cornea, a
convex lens that focuses the light slightly.
2. It passes through a hole called the pupil, which
is controlled by a ring of muscles called the iris.
3. The light passes through the convex lens,
which focuses the light onto the retina.
4. The retina is a layer of light-sensitive cells:
cones for color vision and rods for brightness
5. The rods and cones send electrical impulses
to the brain along the optic nerve.
6. The brain interprets the signals as visual images.

Any Questions

Light and Optics
Part 5: Correcting Vision

Sight Defects
Sometimes, people’s vision is not perfect.
When light does not fall directly on the
retina, images will appear blurry.
This can happen in 2
major ways…
Normal

Sight Defects
Sometimes, people’s vision is not perfect.
When light does not fall directly on the
retina, images will appear blurry.
The eye shape is
not perfectly
spherical.
Long
Short
The lens muscles
do not work
This can
properly.
happen in 2
major ways…
Strong Weak

Nearsightedness
Nearsightedness occurs when light
is focused in front of the retina.
They see well near, but not far.
Causes:
Eye shape is too long
Lens made too thick
Fixed with a concave lens.

Nearsightedness

Farsightedness
Farsightedness occurs when light
is focused behind the retina.
They see well far, but not near.
Causes:
Eye shape is too short
Lens made too thin
Fixed with a convex lens.

Farsightedness

Cataracts
Cataracts cause the lens to become cloudy.
Cataracts are a genetic condition that run
in families, especially African Americans.
Cataracts cause a
person to slowly lose
their vision.
Blindness can result.

Cataracts

Glaucoma
High pressure in the eye causes glaucoma.
Normally, fluid inside the eye is continually
drained away by a drainage canal.
eye fluid
When this canal gets
blocked, fluid builds up
and pressure increases
This pressure pushes on
the lens, affecting vision

Glaucoma

Any Questions