Chemistry_Today_April_2017_vk_com_stopthepress

(Full length)
PHYSICS
SECTION 1 (Maximum Marks : 15)
• This section contains FIVE questions.
• Each question has FOUR options (a), (b), (c) and (d). ONLY
ONE of these four options is correct.
• For each question, darken the bubble corresponding to the
correct option in the ORS.
• For each question, marks will be awarded in one of the following
categories :
Full Marks : +3 If only the bubble corresponding to the correct
option is darkened.
Zero Marks : 0 If none of the bubbles is darkened.
Negative Marks : –1 In all other cases.
1. A photon collides with a stationary hydrogen atom
in ground state inelastically. Energy of the colliding
photon is 10.2 eV. After a time interval of the order
of microsecond, another photon collides with same
hydrogen atom inelastically with an energy of
15 eV. What will be observed by the detector?
(a) One photon of energy 10.2 eV and an electron
of energy 1.4 eV.
(b) Two photons of energy 1.4 eV.
(c) Two photons of energy 10.2 eV.
(d) One photon of energy 10.2 eV and another
photon of 1.4 eV.
2. One end of a uniform rod of length l
A
and mass m is hinged at A. It is
B
released from rest from horizontal
position AB as shown in figure. The
force exerted by the rod on the hinge
when it becomes vertical is
3
(a)
2 mg (b) 5 mg (c) 3 mg (d) 5 mg
2
3. A circular ring of mass 6 kg and radius a is placed
such that its centre lies at the origin. Two particles
of masses 2 kg each are placed at the intersecting
points of the circle with positive x-axis and positive
y-axis. Then the angle made by the position vector
of centre of mass of entire system with x-axis is
(a) 45° (b) 60°
(c) tan –1 (4/5) (d) 30°
PAPER-I
4. To a man moving due north with a speed 5 m s –1 ,
the rain appears to fall vertically. When the man
doubles his speed, the rain appears to fall at 60°.
Find the actual speed of the rain and its direction.
(a) 10 m s –1 , 120° (b) 10 m s –1 , 180°
(c) 10 m s –1 , 90° (d) 10 m s –1 , 60°
5. Magnetic field at the centre of a Bohr’s hypothetical
hydrogen atom in the n th orbit of the electron is
(a) directly proportional to charge of electron e
(b) directly proportional to e 2
(c) inversely proportional to n 5
(d) directly proportional to n 5
SECTION 2 (Maximum Marks : 32)
• This section contains EIGHT questions.
• Each question has FOUR options (a), (b), (c) and (d). ONE OR
MORE THAN ONE of these four option(s) is(are) correct.
• For each question, darken the bubble(s) corresponding to all
the correct option(s) in the ORS.
• For each question, marks will be awarded in one of the following
categories :
Full Marks : +4 If only the bubble(s) corresponding to the
correct option(s) is(are) darkened.
Partial Marks : +1 For darkening a bubble corresponding to
each correct option, provided NO incorrect option is darkened.
Zero Marks : 0 If none of the bubbles is darkened.
Negative Marks : –2 In all other cases.
• For example, if (a), (c) and (d) are all the correct options for
a question, darkening all these three will result in +4 marks;
darkening only (a) and (d) will result in +2 marks; and darkening (a)
and (b) will result in –2 marks, as a wrong option is also darkened.
6. Consider the motion of a positive point charge in
a region where there are simultaneous uniform
electric and magnetic fields ^
E= E j B
0 and = B0
^. j
At time t = 0, this charge has velocity v in the x-y
plane, making an angle θ with the x-axis. Which of
the following option(s) is (are) correct for time t > 0?
(a) If θ = 0°, the charge moves in a circular path in
the x-z plane.
(b) If θ = 0°, the charge undergoes helical motion
with constant pitch along the y-axis.
CHEMISTRY TODAY | APRIL ‘17 27