TIFR GS 2025 Question Paper Physics PhD

FOR TIFR GS EXAM PREPARATION

TIFR GS 2025
Question Paper ·
Physics
EXAM YEAR TYPE SUBJECT DETAILS

TIFR GS 2025 Question Paper Physics PhD

Notes · Sample Papers · Previous Year Papers · Mock Tests

m
m .co

m .co s e m
se g l a
a
Section A
A1 Consider the triangle subtended on the surface of a sphere of radius 1 by joining the
1 √3 1 √3
points ( , , 0), (− , , 0), and (0, 0, 1) with arcs of great circles. The area
2 2 2 2
subtended by this triangle on the surface of the sphere is given by:
m
m .co
.co
(Hint: Drawing a figure might help.)
e m
e m l as
s
(a) a /3
l ag
ag
(b) √3 /2

(c) √3

m
(d) 2 /3
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 1 of 40

A2 The Figure on the right shows a regular
pentagon. The black solid circles on its
vertices represent point charges with
charge – . There is no charge at the
position of the white circle at (measured r
from the origin, O, placed at the centre of
the pentagon). The electric field at O is
given by:

(a) −
=
4 0 3

(b) −4
=
4 0 3

(c)
= 3
4 0

(d) −4 (sin ̂ + cos ̂)
= 10 10
4 2
0

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m
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se g la
A3
a
Consider a two dimensional insulating solid crystal. At low temperature, how does
ℰ
the specific heat at constant area = , where ℰ is the energy per unit area,
depend on ?

(a) 2
∼
m
m .co
(b) ∼ .co
3
s e m
s em l a
g la ∼ ag
a
(c)

(d) is independent of

m
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 3 of 40

A4 The Figure below shows a rocket (red arrow) launched from the earth which is now
at a point where the Earth’s gravitational field is negligible. The rocket thrusters
have stopped. In the rest frame of the Sun, the velocity of the rocket at is same in
magnitude but opposite in direction to that of the earth was, when it was at the same
point. Which of the following statements is correct?

−

(a) The rocket will move exactly on the earth’s elliptical orbit shown in the figure
and eventually collide with the earth

(b) The rocket will eventually escape the Sun’s gravitational field

(c) The rocket will eventually reverse its direction and follow the earth

(d) The rocket will turn towards the sun and eventually collide with it

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m
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m .co s e m
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A5 Water is flowing out of a small horizontal
a
opening of area, , at the bottom of a tank
of height . The flow is a laminar flow H
under the influence of gravity. What is
the area, ′ , of the stream transverse to A
the fluid velocity, at a height ℎ below the h
opening? (Neglect atmospheric pressure A’
m
.co
and dissipation effects. The thickness of
m
.co m
the stream is negligible compared to
and ℎ.)
m s e
s e l a
g l a ag
a(a)
√
ℎ+

(b)
ℎ+

m
m .co
(c) ℎ
(1 + ) s e
g la
a
(d)
ℎ
√1 +

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 5 of 40

A6 A small metallic wire with mass and
electric resistance is bent into a closed
square shape with sides . It passes
through a region of length > with
0
magnetic field ̂ . The initial velocity
0 ̂ of the square is large enough that it
emerges out of from the right. What is
the final velocity of after it completely
emerges from ?

(a) 3 2 2

0 (1 − ) ̂
0

2 2
(b) −
0 0 ̂

(c) 3 2
0 (1 − )̂
0

(d) 0̂

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m
m .co

m .co s e m
se g l a
A7 The output pulse train Y of the circuit
a
shown on the right, with three
synchronized input trains,

= 00001111

= 00110011

m
.co
= 01010101
m
will be: .co s e m
s em l a
g la00010111 ag
a
(a)

(b) 00100111

(c) 01010101
m
m .co
(d) 00010001
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 7 of 40

A8 (NB: Due to a typo in the options all test takers will be awarded the full score.)

Consider a stationary electron in a uniform, time-independent magnetic field of
strength 0 /4 oriented in the ̂ -direction. The Hamiltonian for this system is
expressed as

=− .

where is the spin-1/2 operator for electrons. The initial electron spin is oriented in
the ̂-direction. The spin precession frequency of the electrons is:

(a) | | 0
4

(b) | | 0
8

(c) | | 0
2

(d) 0

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m
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A9 Consider the following space-
a
time diagram which indicates
three events , and for an
inertial observer. Which of the
following statements is true?

m
m .co
m .co s e m
s e l a
g l a ag
a
(a) It is always possible to find an inertial observer for whom events and are
simultaneous. However, no inertial observer can be found for whom events
and are simultaneous.

m
.co
(b) It is always possible to find an inertial observer for whom events and are
simultaneous. However, no inertial observer can be found for whom events
and are simultaneous.
s em
g la
a
(c) It is always possible to find an inertial observer for whom events and are
simultaneous. Similarly, an inertial observer can also be found for whom
events and are simultaneous.

(d) It is impossible to find an inertial observer for whom events and are
simultaneous. Similarly, no inertial observer can be found for whom events
m
m and are simultaneous.
.co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 9 of 40

A10 A massless rigid rod of length is
suspended with an ideal spring of spring
constant at one end , and by a hinge
on the other end, . The rest length of the
spring is zero. A mass is suspended
from the mid-point of the rod. This results
in tilting of the rod by angle . What is
the angle ?

(a) tan−1 ( )
2

(b) sin−1 ( )
2

(c) cos−1 ( )

(d) sec −1 ( )

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A11 There is an open window of dimension
a
(Top view)
1m × 1m on the north east ( ) facing
wall of a house. At 9 AM, the sun shines
through the window and illuminates a Sun rays
certain part of the floor of the house.
What is the area illuminated by the
sun? (Assume that the sun rises in the
m
.co
east ( ) at 6 AM and is directly overhead
m
.co m
( ̂ ) at 12 noon.) ̂
s e
s em l a
(a) la 1 ag
ag √2 m
2

(b) 1 m2

(c) 1 2
m
2
m
m .co
s e
la
(d) √2 m2

ag

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 11 of 40

A12 For a one dimensional quantum harmonic oscillator, at time = 0, the particle is in
the ground state. What is the expectation value of the position and momentum
operator at time ?

(a) 〈 ( )〉 = 〈 ( )〉 = 0

(b) ℏ
〈 ( )〉 = √ sin , 〈 ( )〉 = 0

(c) ℏ
〈 ( )〉 = √ sin , 〈 ( )〉 = √ℏ cos

(d) 〈 ( )〉 = 0, 〈 ( )〉 = √ℏ cos

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m
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m .co s em
se g la
a and respectively such
A13 Consider two ideal gases and with atomic masses
that > . The two gases with same number of moles are kept at the same
temperature and confined in containers with the same volume. Which of the gases
will exert more pressure and molecules of which gas will have a higher RMS
momentum?

m
m .co
(a) .co
Both will exert the same pressure but molecules of Gas will have more
s e m
s em
RMS momentum
l a
g la ag
a(b) Gas will exert more pressure and molecules of Gas will have more RMS
momentum

(c) Gas will exert more pressure but molecules of Gas will have more RMS
momentum

o m
c
. molecules of both gases have the same
m
(d) Both will exert the same pressure and
e
RMS momentum
la s
ag

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 13 of 40

A14 For a given measurement of particles in a counter, a 10-minute data collection
resulted in a statistical uncertainty of 2.5%. How much additional time must be
allocated to reduce the statistical uncertainty to 0.5%?

(a) 240 minutes

(b) 40 minutes

(c) 250 minutes

(d) 50 minutes

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m
m .co

m .co s em
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a
A15 Laser light is incident normally on a thin film of material with a refractive index
( ) larger than that of air ( ≈ 1). As the wavelength of the laser light is varied,
the intensity of the transmitted light through the film shows a peak at 633 nm. If the
thickness of the film is 118 nm, the minimum is closest to:

(a) 2.68
m
o m m .co
(b) 5.36 .c e
em l as
l as ag
g
a(c) 1.34
(d) 3.68

m
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 15 of 40

A16 The asymptotic expansion of the following function for →∞
1
tanh−1

is given by:

(a) 1 1 1
1+ 2
+ 4
+ +⋯
3 5 7 6

(b) 1 1 1
1− 2
+ 4
− +⋯
3 5 7 6

(c) 1 1 1
+ + 3 + 5 +⋯
2 4 6

(d) 1 1 1
1+ 2
+ 4
+ +⋯
2 4 6 6

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a
A17 The × ( > 4) matrix , with all entries equal to 1 has:

(a) Precisely − 1 degenerate eigenvalues and one other non-degenerate
eigenvalue
m
m .co
.co
(b) Precisely − 2 degenerate eigenvalues and two other non-degenerate
s e m
em
eigenvalues
s l a
g la ag
a(c) Precisely 2 degenerate eigenvalues and − 2 other non-degenerate eigenvalues

(d) No degenerate eigenvalues

m
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 17 of 40

A18 A spaceship is moving with a constant
relativistic velocity ̂′ with respect to
an inertial frame ′. In the frame
moving with spaceship, light is emitted
from the source and is detected at the ℎ
detector with displacement ℎ ̂ from . ′
In the frame ′ , what is the time ’ taken
′
for the light to reach from to ? ′

(a) ℎ
( )
√1 − 2/ 2

(b) ℎ
( ) √1 − 2/ 2

(c)
ℎ 1− /
( )√
1+ /

(d) ℎ
( )

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A19 The sinusoidal signal
a
= sin(2 )

is given to a high-pass filter (see Figure).
The output signal is given by

= | |sin(2 + ).
m
m .co
.co
What is the value of | |?
e m
em l as
l as ag
a g
(a) 1
2 1⁄2
1
|1 + ( ) |
2

(b) 1
1
|1 + ( )|
2
m
m .co
(c) 1
s e
|1 + (
1 2
) |
g la
2
a
(d) 1
1⁄2
1
|1 + (2 )|

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 19 of 40

A20 For the circuit on the right, which graph
represents correctly for the
shown below?

(a)

(b)

(c)

(d)

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A21 Light in medium with electric
a
permittivity and magnetic
permeability is incident on a
medium with electric permittivity ′
and magnetic permeability ′. The
angle of incidence is . The field
is linearly polarized in the plane as
m
.co
shown, and the field is in the ̂
m
.co m
direction. Which of the following is
m s e
a correct boundary condition on the
s e l a
a ag
fields?
g l
a
′
(a) ( sin + ′′ sin ) = ′ sin

(b) ( cos − ′′ cos ) = ′ ′ cos

m
.co
(c) sin + ′′ sin = ′ sin

e m
(d) ( + ′′ )
= ′
′ las
ag

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 21 of 40

A22 An experimental set-up needs to be kept in an environment with zero magnetic field
by minimizing the Earth’s magnetic field. This can be achieved by:

(a) Keeping the setup in a place completely covered with a sheet of metal of very
high magnetic permeability

(b) Keeping the setup in a place completely covered with a sheet of metal of very
high permittivity

(c) Keeping the setup at the centre of the interior of a long solenoid

(d) Keeping the setup in a place completely covered with a sheet of an insulating
material

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a
A23 Two types of particles and have the same mass, but are distinguished by an
internal degree of freedom. A classical ideal gas in a volume at temperature
contains ( ) 2 particles of -type and ( ) particles of -type and particles
of -type. Which of the following is true?

m
.co
(a) Pressure of ( ) and ( ) are same; ( ) has more entropy than ( )
m
.co s e m
s em l a
g
(b) laPressure of ( ) and ( ) are same; ( ) has more entropy than ( ) ag
a

(c) Pressure of ( ) is greater than pressure of ( ); ( ) has more entropy than
( )

o m
c
. of ( ); ( ) has more entropy than
m
(d) Pressure of ( ) is greater than pressure
e
( )
la s
a g

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 23 of 40

A24 (NB: Due to an ambiguity in the question all test takers will be awarded the full
score.)

A negative electric charge − moves in a (classical) circular orbit at a non-relativistic
speed around a positive charge. The magnetic field at the centre of the circular orbit
due to the negative charge is found to be 1. Now, consider another situation where
a negative charge −2 moves in a circular orbit at the same speed around the same
positive charge. The magnetic field at the centre of the circular orbit in this case is
2 . What is the ratio 2 / 1 ?

(a) 1/2

(b) 1

(c) 2

(d) 4

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A25 Consider a fan with blades rotating with
a
frequency , as shown in the Figure. It
is used to periodically block a light
beam of intensity 0 . The beam has a
very small cross-sectional area and hits
the blade near its outer edge, as shown.
The transmitted beam is detected by a
m
.co
photo-detection unit which gives out a
m
.co m
voltage signal proportional to the

m
transmitted intensity . If this voltage s e
s e l a
ag
signal pattern is displayed on an
g l a
oscilloscope, what would best describe
athe signal pattern?

(a) 1 4
0[ +∑ sin(2 )], = 2,6,10,14 …
2

m
c. o)],
(b) [cos2 (2 ) − sin2(2
0 ∑ = 2,6,10,14 …

e m
las
g
[ + sin(4 a)]
(c) 1 1
0
2 2

2
(d) 0 [cos (4 )]

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 25 of 40

Section C

C1 Consider two random variables and described by the joint distribution
2 − 2− 2
1 2(1− 2 )
( , )=
2 √1 − 2

with 0 < < 1. If the above distribution is written in terms of orthogonal coordinates
= − and = + , the probability distribution in is given by:

(a) A Gaussian with mean 0 and standard deviation √2(1 − )

(b) A Gaussian with mean √ and standard deviation √2(1 − )

(c) A Gaussian with mean 0 and standard deviation √2(1 − 2)

(d) Not a Gaussian distribution

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m
m .co

m .co s em
se g la
C2 Consider a particle with mass
a
in a quantum harmonic oscillator potential with a
frequency , such that its Hamiltonian is

̂2 2 2
̂
̂= +
2 2
The Hamiltonian is perturbed by adding a term to the potential

m
.co
Δ ̂ = sin ̂
m
.co
where is small compared to ℏ . The relative change in the ground state energy, to
m s e m
e
the leading order in /(ℏ ) is given by:
s l a
g l a ag
a(a) 2
( )
(ℏ )2

(b)
( )
(ℏ )

m
.co
em
(c) (1)

las
g
a does not change
(d) The ground state energy

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 27 of 40

C3 A relativistic particle moving under the central force of gravity experiences the
following effective potential:
2 2
eff ( ) = − + 2
− 2 3
2
where the last term is the relativistic correction to the Newtonian formula. The
smallest radius at which a stable circular orbit can exist for some value of the angular
momentum is given by:

(a) 6
2

(b) 3
2

(c) 2
2

(d) There are no stable circular orbits

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m .co

m .co s em
se g la
C4
a
(NB: Due to an ambiguity in the question all test takers will be awarded the full
score.)

The integral
+∞ −
∫ 2+1
−∞

m
.co
is given by:
m
m .co s e m
s e l a
ag
(a) −

g l a
a
(b)

(c) −
−

(d) −
m
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 29 of 40

C5 Consider a (non-relativistic) gas of fermions in a container with a fixed density .
Which plot best describes how the chemical potential changes with ?

(a)

(b)

(c)

(d)

For more Question Papers, Sample Papers, Notes & Syllabus visit Page 30 of 40

m
m .co

m .co s e m
se g l a
C6 A triangular lattice with lattice constant a
a
has primitive vectors ⃗⃗⃗⃗1 and ⃗⃗⃗⃗2 , as
shown in the Figure. The primitive
wavevectors for the reciprocal lattice are
given by:

m
m .co
.co s e m
s em l a
(a) la⃗⃗⃗
g 2 2 4 ag
a 1 = ̂ +
√3
̂, ⃗⃗⃗⃗2 =
√3
̂

(b) 2 2 4
⃗⃗⃗1 = ̂+ ̂, ⃗⃗⃗⃗2 = ̂
√3 √3

(c) 2 2 4
m
c. o ̂
⃗⃗⃗1 = ̂ − ̂, ⃗⃗⃗⃗2 =
√3 √3

s em
g la⃗⃗⃗⃗ 4
̂ ,a
(d) 2 2
⃗⃗⃗ =
1 ̂− = ̂ 2
√3 √3

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 31 of 40

C7 Consider a free-particle in 3 spatial dimensions described by the Hamiltonian

̂
̂=
2
It is initially in a state described by a normalized wavefunction
3/4
− 2 /2
( , = 0) = ( ) .

What is the probability density of finding the particle with energy at time ?

(Hint: Express the wavefunction in momentum space.)
+∞ 1 − − 2 /2 1 − 2 /(2 )
(The following integral might be useful: ∫−∞ = .)
√2 √

(a) 4
( )−3/2 √2 −2 /( ℏ^2)
ℏ3

(b)
4 2 ℏ
( )−3/2 √ −2 /( ℏ^2)
ℏ3

(c) 2 1
( )−1/2 −2 /( ℏ^2)
ℏ √2

(d) 2
( )−1 −2 /( ℏ^2)
ℏ2

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m
m .co

m .co s em
se g la
C8
a
Consider two relativistic particles, each with mass and momentum of magnitude
, colliding head-on. As a result of the collision, two heavier particles are produced,
each with mass , where > 1. The minimum value of required for this collision
to occur is:

(a) √ 2−1
m
c o m m .co
. s e
em a
(b) ( − 1)
s l
g la ag
a(c) 2

(d) (√ − 1)2

m
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 33 of 40

C9 Consider a particle moving on a one-dimensional discrete lattice with lattice
constant . can hop from one site to a neighbouring site. The probabilities of
moving to the right and left are and = 1 − , respectively. Starting from the
origin = 0 at time = 0, what is the mean square displacement 〈( − 〈 〉)2 〉
after steps, where 〈 〉 is the average position at time ?

(a) 2
4

(b) 2
4 ( − )

(c) 2
2

(d) 2
2 ( − )

For more Question Papers, Sample Papers, Notes & Syllabus visit Page 34 of 40

m
m .co

m .co s em
se g la
C10
a
In the shell model of a nucleus, states of nucleons (protons or neutrons) in a
spherically symmetric potential are labelled as , where is the principal
quantum number, is the angular momentum quantum number ( , , ,
correspond to = 0,1,2,3 respectively), and ̂ = ̂ + ̂ . The spin-orbit interaction is
given by

̂ = ̂. ̂
m
m
If the strength of spin-orbit interaction is = −2 MeV, the energy difference
.co
.co
between two nucleonic states 1 5/2 and 1 3/2 is given by:
s e m
s em l a
g la5 MeV ag
a
(a)

(b) 2 MeV

(c) 3 MeV

m
(d) 4 MeV
m .co
s e
g la
a

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 35 of 40

C11 (NB: Due to a typo in the options all test
takers will be awarded the full score.)

A perfect mirror is hanging from the
ceiling via a spring of spring constant .
Δ
A plane wave laser beam with area
and

( , )= 0 ̂ cos( . − )

is incident on the mirror at an angle ,
and lifts the mirror by Δ . What is Δ
(averaged over a cycle) in terms of
, 0 , 0 , and 0 ?

(a) 2
cos
0 0
√
0

(b) 2
cos 2
0 0
√
0

(c) 2
0 0 0
√
0

(d) 2 0 02 cos 2 0
√
0

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m
m .co

m .co s e m
se g l a
C12 A composite pendulum consists of two
a
massless rods and a weight . The two
rods are connected by a hinge ′. The 1

other end of the first rod is connected to
′
the ceiling by a hinge . The rods can
move freely about , ′ in the plane.
What is the Lagrangian of the system? 2
m
m .co
m .co s e m
s e l a
(a) a
l 2
( ̇ + ̇ + 2 ̇ ̇ cos( − ))
2 2
ag
ag
1 2 1 2 1 2
+ (cos 1 + cos 2 )
2

(b) 2
( ̇12 + ̇22 )
+ (cos 1 + cos 2 )
2

(c) 2
( ̇12 + ̇22 + 2 ̇1 ̇ 2 sin( 1 − 2 ))
−m (cos + cos )
2
.c o 1 2

s em
(d) 2 2 2
g la − )) −
( ̇ + ̇ − 2 ̇ ̇ cos(
2 a
1 2 1 2 1 2
(cos 1 + cos 2 )

m
m .co
m .co s e m
s e g l a
g la a
a

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 37 of 40

C13 Consider the alpha decay of 224U at rest, to 220Th. The atomic masses are given
below:

M224U = 224.0276 amu; M220Th = 220.0158 amu; M4He = 4.0026 amu.

What is the estimate of the kinetic energy of the emitted alpha (4He) particle? (One
amu corresponds to 931.5 MeV/c 2 .)

(a) 8.4163 MeV

(b) 8.5698 MeV

(c) 8.7261 MeV

(d) 8.1066 MeV

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m
m .co

m .co s em
se g la
a
C14 Two students perform a counting experiment independently. Student A measures the
counts for 1-minute intervals each and repeats the measurement five times. The
obtained counts are given below.

Measurement turn Counts

1 25

m
.co
2 35
m
m .co 3 30
s e m
s e l a
g l a 4 23
ag
a 5 27

This student then takes the mean of these counts and reports the count rate
(counts/min). The second student (B) makes one measurement for five minutes. She
measures 145 counts and reports the count rate (counts/min). If the clock used for all
these measurements is accurate up to 0.1 minutes, and there are no other sources of
uncertainties, we can conclude that:

o m
(a) The count rate reported by studentm
c
A .will have a larger uncertainty than that
s e
la
reported by student B.

a g
(b) The count rate reported by student B will have a larger uncertainty than that
reported by student A.

(c) The reported uncertainty in both results would be identical

m
m .co
.co
(d) Nothing may be concluded about the relative uncertainties between A and B
e m
e m l as
las ag
ag

m .
.co s e m
s em l a
g la ag
a For more Question Papers, Sample Papers, Notes & Syllabus visit Page 39 of 40

C15 2 is a linear molecule. (The bond length of the oxygen molecule is 1.2Å, and the
mass of an oxygen atom is 2.7 × 10−26 kg.) A neutron strikes an 2 molecule and
loses energy by exciting a rotational energy level of 2 .Which of the following is
the best estimate of the lowest amount of energy the neutron would have to transfer
to the 2 molecule? (Take the transfer of translational kinetic energy to be
negligible.)

(a) 3.6 × 10−4 eV

(b) 7.2 × 10−4 eV

(c) 1.8 × 10−4 eV

(d) 1.4 × 10−3 eV

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