JEE Main 2021 Physics February 25 Shift 2 Paper & Solutions | Mock Tests for JEE Main and Advanced 2025 PDF Download

 Page 1


JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
PART–A : PHYSICS
SECTION - I
Multiple Choice Questions: This section contains
20 multiple choice questions. Each question has
4 choices (1), (2), (3) and (4), out of which ONL Y ONE
is correct.
Choose the correct answer :
1. The truth table for the following logic circuit is
Y
A
B
(1) AB Y
00 0
01 1
10 1
11 0
(2) AB Y
00 1
01 0
10 1
11 0
(3) AB Y
00 1
01 0
10 0
11 1
(4) AB Y
00 0
01 1
10 0
11 1
Answer (3)
Sol. Truth table
AB C AB D AB C D C D Y
00 0 0 0 1
01 0 1 1 0
10 1 0 1 0
11 0 0 0 1
?? ?? ? ? ?
2. Match List I with List II.
List I List II
(a)Rectifier (i) Used either for
stepping up or
stepping down the
a.c. voltage
(b) Stabilizer (ii) Used to convert a.c.
voltage into d.c.
voltage
(c) Transformer (iii) Used to remove any
ripple in the
rectified output
voltage
(d) Filter (iv) Used for constant
output voltage even
when the input
voltage or load
current change
Choose the correct answer from the options
given below :
(1) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
(2) (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
(3) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(4) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Answer (2)
Sol. Correct match are
a ? (ii)
b ? (iv)
c ? (i)
d ? (iii)
3. A stone is dropped from the top of a building.
When it crosses a point 5 m below the top,
another stone starts to fall from a point 25 m
below the top. Both stones reach the bottom of
building simultaneously. The height of the
building is
(1) 35 m
(2) 45 m
(3) 25 m
(4) 50 m
Answer (2)
Sol.
2
11
1
510t t1s
2
?? ? ? ?
? v
1
 = gt
1
 = 10 m/s
Time of collision,
20 m
v
1
20
t2s
10
?? ?
? Total time of fall = 3 s
?
2
1
H (10)345m
2
?? ? ?
Page 2


JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
PART–A : PHYSICS
SECTION - I
Multiple Choice Questions: This section contains
20 multiple choice questions. Each question has
4 choices (1), (2), (3) and (4), out of which ONL Y ONE
is correct.
Choose the correct answer :
1. The truth table for the following logic circuit is
Y
A
B
(1) AB Y
00 0
01 1
10 1
11 0
(2) AB Y
00 1
01 0
10 1
11 0
(3) AB Y
00 1
01 0
10 0
11 1
(4) AB Y
00 0
01 1
10 0
11 1
Answer (3)
Sol. Truth table
AB C AB D AB C D C D Y
00 0 0 0 1
01 0 1 1 0
10 1 0 1 0
11 0 0 0 1
?? ?? ? ? ?
2. Match List I with List II.
List I List II
(a)Rectifier (i) Used either for
stepping up or
stepping down the
a.c. voltage
(b) Stabilizer (ii) Used to convert a.c.
voltage into d.c.
voltage
(c) Transformer (iii) Used to remove any
ripple in the
rectified output
voltage
(d) Filter (iv) Used for constant
output voltage even
when the input
voltage or load
current change
Choose the correct answer from the options
given below :
(1) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
(2) (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
(3) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(4) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Answer (2)
Sol. Correct match are
a ? (ii)
b ? (iv)
c ? (i)
d ? (iii)
3. A stone is dropped from the top of a building.
When it crosses a point 5 m below the top,
another stone starts to fall from a point 25 m
below the top. Both stones reach the bottom of
building simultaneously. The height of the
building is
(1) 35 m
(2) 45 m
(3) 25 m
(4) 50 m
Answer (2)
Sol.
2
11
1
510t t1s
2
?? ? ? ?
? v
1
 = gt
1
 = 10 m/s
Time of collision,
20 m
v
1
20
t2s
10
?? ?
? Total time of fall = 3 s
?
2
1
H (10)345m
2
?? ? ?
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
4. The point A moves with a uniform speed along
the circumference of a circle of radius 0.36 m
and covers 30° in 0.1 s. The perpendicular
projection ‘P’ from ‘A’ on the diameter MN
represents the simple harmonic motion of ‘P’.
The restoration force per unit mass when P
touches M will be
30°
A
P
N M
O
0.1 s
0.36 m
(1) 9.87 N (2) 50 N
(3) 100 N (4) 0.49 N
Answer (1)
Sol. 
(0.36)
6
vm/s
0.1
? ??
?
??
??
?
= ? × 0.6 m/s
?
22
2
M
v ( 0.6)
a9.87N/kg
r0.36
??
?? ???
5. An LCR circuit contains resistance of 110 ?
and a supply of 220 V at 300 rad/s angular
frequency. If only capacitance is removed from
the circuit, current lags behind the voltage by
45°. If on the other hand, only inductor is
removed the current leads by 45° with the
applied voltage. The rms current flowing in the
circuit will be
(1) 1.5 A (2) 1 A
(3) 2 A (4) 2.5 A
Answer (3)
Sol. LCR circuit is in resonance.
? ? ? ? ?
rms
rms
V 220
I2A
R110
?? ?
6. Consider the diffraction pattern obtained from
the sunlight incident on a pinhole of diameter
0.1 ?m. If the diameter of the pinhole is slightly
increased, it will affect the diffraction pattern
such that
(1) Its size decreases, and intensity decreases
(2) Its size increases, and intensity increases
(3) Its size increases, but intensity decreases
(4) Its size decreases, but intensity increases
Answer (4)
Sol.
?
? ?
dark
1.22 D
r
b
, where b is opening diameter .
When opening size is increased, the diffraction
size decreases but intensity increases.
7. Thermodynamic process is shown below on a
P-V diagram for one mole of an ideal gas. If
V
2
 = 2V
1
 then the ratio of temperature T
2
/T
1
 is
P 1(P , V , T )
111
PV
1
2
= constant
2(P , V , T )
222
V
1
V
2
V
(1) 2 (2) 2
(3)
1
2
(4)
1
2
Answer (1)
Sol. ?
1/2
PV constant
?
1/2
T
V
V
 = constant
? ? TV
?? ?
22
11
TV 2
TV 1
? ?
2
1
T
2
T
8. An electron of mass m
e
 and a proton of mass
m
p
 = 1836m
e
 are moving with the same speed.
The ratio of their de Broglie wavelength
?
?
electron
proton
 will be
(1)
1
1836
(2) 918
(3) 1 (4) 1836
Answer (4)
Sol. ??
?
e
e
h
mv
??
?
p
p
h
mv
?
? ??
?
p
e
pe
m
1836
m
Page 3


JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
PART–A : PHYSICS
SECTION - I
Multiple Choice Questions: This section contains
20 multiple choice questions. Each question has
4 choices (1), (2), (3) and (4), out of which ONL Y ONE
is correct.
Choose the correct answer :
1. The truth table for the following logic circuit is
Y
A
B
(1) AB Y
00 0
01 1
10 1
11 0
(2) AB Y
00 1
01 0
10 1
11 0
(3) AB Y
00 1
01 0
10 0
11 1
(4) AB Y
00 0
01 1
10 0
11 1
Answer (3)
Sol. Truth table
AB C AB D AB C D C D Y
00 0 0 0 1
01 0 1 1 0
10 1 0 1 0
11 0 0 0 1
?? ?? ? ? ?
2. Match List I with List II.
List I List II
(a)Rectifier (i) Used either for
stepping up or
stepping down the
a.c. voltage
(b) Stabilizer (ii) Used to convert a.c.
voltage into d.c.
voltage
(c) Transformer (iii) Used to remove any
ripple in the
rectified output
voltage
(d) Filter (iv) Used for constant
output voltage even
when the input
voltage or load
current change
Choose the correct answer from the options
given below :
(1) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
(2) (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
(3) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(4) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Answer (2)
Sol. Correct match are
a ? (ii)
b ? (iv)
c ? (i)
d ? (iii)
3. A stone is dropped from the top of a building.
When it crosses a point 5 m below the top,
another stone starts to fall from a point 25 m
below the top. Both stones reach the bottom of
building simultaneously. The height of the
building is
(1) 35 m
(2) 45 m
(3) 25 m
(4) 50 m
Answer (2)
Sol.
2
11
1
510t t1s
2
?? ? ? ?
? v
1
 = gt
1
 = 10 m/s
Time of collision,
20 m
v
1
20
t2s
10
?? ?
? Total time of fall = 3 s
?
2
1
H (10)345m
2
?? ? ?
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
4. The point A moves with a uniform speed along
the circumference of a circle of radius 0.36 m
and covers 30° in 0.1 s. The perpendicular
projection ‘P’ from ‘A’ on the diameter MN
represents the simple harmonic motion of ‘P’.
The restoration force per unit mass when P
touches M will be
30°
A
P
N M
O
0.1 s
0.36 m
(1) 9.87 N (2) 50 N
(3) 100 N (4) 0.49 N
Answer (1)
Sol. 
(0.36)
6
vm/s
0.1
? ??
?
??
??
?
= ? × 0.6 m/s
?
22
2
M
v ( 0.6)
a9.87N/kg
r0.36
??
?? ???
5. An LCR circuit contains resistance of 110 ?
and a supply of 220 V at 300 rad/s angular
frequency. If only capacitance is removed from
the circuit, current lags behind the voltage by
45°. If on the other hand, only inductor is
removed the current leads by 45° with the
applied voltage. The rms current flowing in the
circuit will be
(1) 1.5 A (2) 1 A
(3) 2 A (4) 2.5 A
Answer (3)
Sol. LCR circuit is in resonance.
? ? ? ? ?
rms
rms
V 220
I2A
R110
?? ?
6. Consider the diffraction pattern obtained from
the sunlight incident on a pinhole of diameter
0.1 ?m. If the diameter of the pinhole is slightly
increased, it will affect the diffraction pattern
such that
(1) Its size decreases, and intensity decreases
(2) Its size increases, and intensity increases
(3) Its size increases, but intensity decreases
(4) Its size decreases, but intensity increases
Answer (4)
Sol.
?
? ?
dark
1.22 D
r
b
, where b is opening diameter .
When opening size is increased, the diffraction
size decreases but intensity increases.
7. Thermodynamic process is shown below on a
P-V diagram for one mole of an ideal gas. If
V
2
 = 2V
1
 then the ratio of temperature T
2
/T
1
 is
P 1(P , V , T )
111
PV
1
2
= constant
2(P , V , T )
222
V
1
V
2
V
(1) 2 (2) 2
(3)
1
2
(4)
1
2
Answer (1)
Sol. ?
1/2
PV constant
?
1/2
T
V
V
 = constant
? ? TV
?? ?
22
11
TV 2
TV 1
? ?
2
1
T
2
T
8. An electron of mass m
e
 and a proton of mass
m
p
 = 1836m
e
 are moving with the same speed.
The ratio of their de Broglie wavelength
?
?
electron
proton
 will be
(1)
1
1836
(2) 918
(3) 1 (4) 1836
Answer (4)
Sol. ??
?
e
e
h
mv
??
?
p
p
h
mv
?
? ??
?
p
e
pe
m
1836
m
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
9. The wavelength of the photon emitted by a
hydrogen atom when an electron makes a
transition from n = 2 to n = 1 state is
(1) 490.7 nm (2) 121.8 nm
(3) 913.3 nm (4) 194.8 nm
Answer (2)
Sol.
??
??
??
?
??
22
111
R
12
    
??
??
??
??
3
R
4
? ?? ?
??
7
44
3R
31.0910
         = 121.8 nm
10. For extrinsic semiconductors; when doping
level is increased;
(1) Fermi-level of p-type semiconductors will
go downward and Fermi-level of n-type
semiconductor will go upward.
(2) Fermi-level of p and n-type semiconductors
will not be affected.
(3) Fermi-level of both p-type and n-type
semiconductors will go upward for T > T
F 
K
and downward for T < T
F 
K, where T
F
 is
Fermi temperature.
(4) Fermi-level of p-type semiconductor will go
upward and Fermi-level of n-type
semiconductors will go downward.
Answer (1)
Sol. Fermi-level of p type semiconductor goes down
whereas it goes up for n-type semiconductor.
11. Y = Asin( ?t + ?
0
) is the time-displacement
equation of a SHM. At t = 0 the displacement of
the particle is 
?
A
Y
2
 and it is moving along
negative x-direction. Then the initial phase
angle ?
0
 will be:
(1)
?
6
(2)
? 2
3
(3)
? 5
6
(4)
?
3
Answer (3)
Sol. Draw phasor :
B A
?
?/6 ?/6
At B particle is going toward mean position
? negative x-direction
?
??
5
6
12. The stopping potential for electrons emitted
from a photosensitive surface illuminated by
light of wavelength 491 nm is 0.710 V. When the
incident wavelength is changed to a new value,
the stopping potential is 1.43 V. The new
wavelength is :
(1) 329 nm (2) 400 nm
(3) 382 nm (4) 309 nm
Answer (3)
Sol. ?? ?
?
hc
eV
?? ?
??
12
12
hc hc
eV eV
?? ?
?
2
1240 1240
0.71 1.43
491
??
?
2
1240 1240
0.72
491
?
2
 = 382 nm
13. If a message signal of frequency ‘f
m
’ is
amplitude modulated with a carrier signal of
frequency ‘f
c
’ and radiated through an antenna,
the wavelength of the corresponding signal in
air is:
(1)
c
c
f
(2)
m
c
f
(3)
?
cm
c
ff
(4)
?
cm
c
ff
Answer (1)
Sol.In amplitude modulated wave, wave is
transmitted at frequency of carrier wave
??
c
c
f
14. Given below are two statements :
Statement I : In a diatomic molecule, the
rotational energy at a given
temperature obeys Maxwell’s
distribution.
Statement II : In a diatomic molecule, the
rotational energy at a given
temperature equals the
translational kinetic energy for
each molecule.
Page 4


JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
PART–A : PHYSICS
SECTION - I
Multiple Choice Questions: This section contains
20 multiple choice questions. Each question has
4 choices (1), (2), (3) and (4), out of which ONL Y ONE
is correct.
Choose the correct answer :
1. The truth table for the following logic circuit is
Y
A
B
(1) AB Y
00 0
01 1
10 1
11 0
(2) AB Y
00 1
01 0
10 1
11 0
(3) AB Y
00 1
01 0
10 0
11 1
(4) AB Y
00 0
01 1
10 0
11 1
Answer (3)
Sol. Truth table
AB C AB D AB C D C D Y
00 0 0 0 1
01 0 1 1 0
10 1 0 1 0
11 0 0 0 1
?? ?? ? ? ?
2. Match List I with List II.
List I List II
(a)Rectifier (i) Used either for
stepping up or
stepping down the
a.c. voltage
(b) Stabilizer (ii) Used to convert a.c.
voltage into d.c.
voltage
(c) Transformer (iii) Used to remove any
ripple in the
rectified output
voltage
(d) Filter (iv) Used for constant
output voltage even
when the input
voltage or load
current change
Choose the correct answer from the options
given below :
(1) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
(2) (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
(3) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(4) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Answer (2)
Sol. Correct match are
a ? (ii)
b ? (iv)
c ? (i)
d ? (iii)
3. A stone is dropped from the top of a building.
When it crosses a point 5 m below the top,
another stone starts to fall from a point 25 m
below the top. Both stones reach the bottom of
building simultaneously. The height of the
building is
(1) 35 m
(2) 45 m
(3) 25 m
(4) 50 m
Answer (2)
Sol.
2
11
1
510t t1s
2
?? ? ? ?
? v
1
 = gt
1
 = 10 m/s
Time of collision,
20 m
v
1
20
t2s
10
?? ?
? Total time of fall = 3 s
?
2
1
H (10)345m
2
?? ? ?
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
4. The point A moves with a uniform speed along
the circumference of a circle of radius 0.36 m
and covers 30° in 0.1 s. The perpendicular
projection ‘P’ from ‘A’ on the diameter MN
represents the simple harmonic motion of ‘P’.
The restoration force per unit mass when P
touches M will be
30°
A
P
N M
O
0.1 s
0.36 m
(1) 9.87 N (2) 50 N
(3) 100 N (4) 0.49 N
Answer (1)
Sol. 
(0.36)
6
vm/s
0.1
? ??
?
??
??
?
= ? × 0.6 m/s
?
22
2
M
v ( 0.6)
a9.87N/kg
r0.36
??
?? ???
5. An LCR circuit contains resistance of 110 ?
and a supply of 220 V at 300 rad/s angular
frequency. If only capacitance is removed from
the circuit, current lags behind the voltage by
45°. If on the other hand, only inductor is
removed the current leads by 45° with the
applied voltage. The rms current flowing in the
circuit will be
(1) 1.5 A (2) 1 A
(3) 2 A (4) 2.5 A
Answer (3)
Sol. LCR circuit is in resonance.
? ? ? ? ?
rms
rms
V 220
I2A
R110
?? ?
6. Consider the diffraction pattern obtained from
the sunlight incident on a pinhole of diameter
0.1 ?m. If the diameter of the pinhole is slightly
increased, it will affect the diffraction pattern
such that
(1) Its size decreases, and intensity decreases
(2) Its size increases, and intensity increases
(3) Its size increases, but intensity decreases
(4) Its size decreases, but intensity increases
Answer (4)
Sol.
?
? ?
dark
1.22 D
r
b
, where b is opening diameter .
When opening size is increased, the diffraction
size decreases but intensity increases.
7. Thermodynamic process is shown below on a
P-V diagram for one mole of an ideal gas. If
V
2
 = 2V
1
 then the ratio of temperature T
2
/T
1
 is
P 1(P , V , T )
111
PV
1
2
= constant
2(P , V , T )
222
V
1
V
2
V
(1) 2 (2) 2
(3)
1
2
(4)
1
2
Answer (1)
Sol. ?
1/2
PV constant
?
1/2
T
V
V
 = constant
? ? TV
?? ?
22
11
TV 2
TV 1
? ?
2
1
T
2
T
8. An electron of mass m
e
 and a proton of mass
m
p
 = 1836m
e
 are moving with the same speed.
The ratio of their de Broglie wavelength
?
?
electron
proton
 will be
(1)
1
1836
(2) 918
(3) 1 (4) 1836
Answer (4)
Sol. ??
?
e
e
h
mv
??
?
p
p
h
mv
?
? ??
?
p
e
pe
m
1836
m
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
9. The wavelength of the photon emitted by a
hydrogen atom when an electron makes a
transition from n = 2 to n = 1 state is
(1) 490.7 nm (2) 121.8 nm
(3) 913.3 nm (4) 194.8 nm
Answer (2)
Sol.
??
??
??
?
??
22
111
R
12
    
??
??
??
??
3
R
4
? ?? ?
??
7
44
3R
31.0910
         = 121.8 nm
10. For extrinsic semiconductors; when doping
level is increased;
(1) Fermi-level of p-type semiconductors will
go downward and Fermi-level of n-type
semiconductor will go upward.
(2) Fermi-level of p and n-type semiconductors
will not be affected.
(3) Fermi-level of both p-type and n-type
semiconductors will go upward for T > T
F 
K
and downward for T < T
F 
K, where T
F
 is
Fermi temperature.
(4) Fermi-level of p-type semiconductor will go
upward and Fermi-level of n-type
semiconductors will go downward.
Answer (1)
Sol. Fermi-level of p type semiconductor goes down
whereas it goes up for n-type semiconductor.
11. Y = Asin( ?t + ?
0
) is the time-displacement
equation of a SHM. At t = 0 the displacement of
the particle is 
?
A
Y
2
 and it is moving along
negative x-direction. Then the initial phase
angle ?
0
 will be:
(1)
?
6
(2)
? 2
3
(3)
? 5
6
(4)
?
3
Answer (3)
Sol. Draw phasor :
B A
?
?/6 ?/6
At B particle is going toward mean position
? negative x-direction
?
??
5
6
12. The stopping potential for electrons emitted
from a photosensitive surface illuminated by
light of wavelength 491 nm is 0.710 V. When the
incident wavelength is changed to a new value,
the stopping potential is 1.43 V. The new
wavelength is :
(1) 329 nm (2) 400 nm
(3) 382 nm (4) 309 nm
Answer (3)
Sol. ?? ?
?
hc
eV
?? ?
??
12
12
hc hc
eV eV
?? ?
?
2
1240 1240
0.71 1.43
491
??
?
2
1240 1240
0.72
491
?
2
 = 382 nm
13. If a message signal of frequency ‘f
m
’ is
amplitude modulated with a carrier signal of
frequency ‘f
c
’ and radiated through an antenna,
the wavelength of the corresponding signal in
air is:
(1)
c
c
f
(2)
m
c
f
(3)
?
cm
c
ff
(4)
?
cm
c
ff
Answer (1)
Sol.In amplitude modulated wave, wave is
transmitted at frequency of carrier wave
??
c
c
f
14. Given below are two statements :
Statement I : In a diatomic molecule, the
rotational energy at a given
temperature obeys Maxwell’s
distribution.
Statement II : In a diatomic molecule, the
rotational energy at a given
temperature equals the
translational kinetic energy for
each molecule.
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
In the light of the above statements, choose the
correct answer from the options given below:
(1) Both Statement I and Statement II are false.
(2) Statement I is false but Statement II is true.
(3) Statement I is true but Statement II is false.
(4) Both Statement I and Statement II are true.
Answer (3)
Sol. K
R
 = kT
T
3
KkT
2
?
K
T
 for each molecule
3
kT
4
15. A charge ‘q’ is placed at one corner of a cube
as shown in figure. The flux of electrostatic
field 

E
 through the shaded area is:
X
Y
Z
q
(1)
?
0
q
4
(2)
?
0
q
24
(3)
?
0
q
48
(4)
?
0
q
8
Answer (2)
Sol. Complete the cube with double the side with
charge at centre
flux, ?? ? ?
??
00
1qq
38 24
16. An electron with kinetic energy K
1
 enters
between parallel plates of a capacitor at an
angle ‘ ?’ with the plates. It leaves the plates at
angle ‘ ?’ with kinetic energy K
2
. Then the ratio
of kinetic energies K
1
 : K
2
 will be :
(1)
?
?
cos
sin
(2)
?
?
cos
cos
(3)
?
?
2
2
cos
cos
(4)
?
?
2
2
sin
cos
Answer (3)
Sol. v
1
cos ? = v
2
cos ?
?
??
?
2 2
11
22
2
2
Kv cos
K
vcos
v
1
v
2
?
?
17. In a ferromagnetic material, below the curie
temperature, a domain is defined as :
(1) a macroscopic region with randomly
oriented magnetic dipoles.
(2) a macroscopic region with consecutive
magnetic dipoles oriented in opposite
direction.
(3) a macroscopic region with saturation
magnetization.
(4)a macroscopic region with zero
magnetization.
Answer (3)
Sol. Domain is the region in which magnetic
moment is aligned in such a way to produce
saturated magnetization.
18. Two identical springs of spring constant ‘2k’
are attached to a block of mass m and to fixed
support (see figure). When the mass is
displaced from equilibrium position on either
side, it executes simple harmonic motion. The
time period of oscillations of this system is :
2k 2k
m
(1)
?
m
k
(2)
?
m
2k
(3)
?
m
2
2k
(4)
?
m
2
k
Answer (1)
Sol. ??
eq
m
T2
k
?
eq
k4k
??
m
T
k
Page 5


JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
PART–A : PHYSICS
SECTION - I
Multiple Choice Questions: This section contains
20 multiple choice questions. Each question has
4 choices (1), (2), (3) and (4), out of which ONL Y ONE
is correct.
Choose the correct answer :
1. The truth table for the following logic circuit is
Y
A
B
(1) AB Y
00 0
01 1
10 1
11 0
(2) AB Y
00 1
01 0
10 1
11 0
(3) AB Y
00 1
01 0
10 0
11 1
(4) AB Y
00 0
01 1
10 0
11 1
Answer (3)
Sol. Truth table
AB C AB D AB C D C D Y
00 0 0 0 1
01 0 1 1 0
10 1 0 1 0
11 0 0 0 1
?? ?? ? ? ?
2. Match List I with List II.
List I List II
(a)Rectifier (i) Used either for
stepping up or
stepping down the
a.c. voltage
(b) Stabilizer (ii) Used to convert a.c.
voltage into d.c.
voltage
(c) Transformer (iii) Used to remove any
ripple in the
rectified output
voltage
(d) Filter (iv) Used for constant
output voltage even
when the input
voltage or load
current change
Choose the correct answer from the options
given below :
(1) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
(2) (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
(3) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(4) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Answer (2)
Sol. Correct match are
a ? (ii)
b ? (iv)
c ? (i)
d ? (iii)
3. A stone is dropped from the top of a building.
When it crosses a point 5 m below the top,
another stone starts to fall from a point 25 m
below the top. Both stones reach the bottom of
building simultaneously. The height of the
building is
(1) 35 m
(2) 45 m
(3) 25 m
(4) 50 m
Answer (2)
Sol.
2
11
1
510t t1s
2
?? ? ? ?
? v
1
 = gt
1
 = 10 m/s
Time of collision,
20 m
v
1
20
t2s
10
?? ?
? Total time of fall = 3 s
?
2
1
H (10)345m
2
?? ? ?
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
4. The point A moves with a uniform speed along
the circumference of a circle of radius 0.36 m
and covers 30° in 0.1 s. The perpendicular
projection ‘P’ from ‘A’ on the diameter MN
represents the simple harmonic motion of ‘P’.
The restoration force per unit mass when P
touches M will be
30°
A
P
N M
O
0.1 s
0.36 m
(1) 9.87 N (2) 50 N
(3) 100 N (4) 0.49 N
Answer (1)
Sol. 
(0.36)
6
vm/s
0.1
? ??
?
??
??
?
= ? × 0.6 m/s
?
22
2
M
v ( 0.6)
a9.87N/kg
r0.36
??
?? ???
5. An LCR circuit contains resistance of 110 ?
and a supply of 220 V at 300 rad/s angular
frequency. If only capacitance is removed from
the circuit, current lags behind the voltage by
45°. If on the other hand, only inductor is
removed the current leads by 45° with the
applied voltage. The rms current flowing in the
circuit will be
(1) 1.5 A (2) 1 A
(3) 2 A (4) 2.5 A
Answer (3)
Sol. LCR circuit is in resonance.
? ? ? ? ?
rms
rms
V 220
I2A
R110
?? ?
6. Consider the diffraction pattern obtained from
the sunlight incident on a pinhole of diameter
0.1 ?m. If the diameter of the pinhole is slightly
increased, it will affect the diffraction pattern
such that
(1) Its size decreases, and intensity decreases
(2) Its size increases, and intensity increases
(3) Its size increases, but intensity decreases
(4) Its size decreases, but intensity increases
Answer (4)
Sol.
?
? ?
dark
1.22 D
r
b
, where b is opening diameter .
When opening size is increased, the diffraction
size decreases but intensity increases.
7. Thermodynamic process is shown below on a
P-V diagram for one mole of an ideal gas. If
V
2
 = 2V
1
 then the ratio of temperature T
2
/T
1
 is
P 1(P , V , T )
111
PV
1
2
= constant
2(P , V , T )
222
V
1
V
2
V
(1) 2 (2) 2
(3)
1
2
(4)
1
2
Answer (1)
Sol. ?
1/2
PV constant
?
1/2
T
V
V
 = constant
? ? TV
?? ?
22
11
TV 2
TV 1
? ?
2
1
T
2
T
8. An electron of mass m
e
 and a proton of mass
m
p
 = 1836m
e
 are moving with the same speed.
The ratio of their de Broglie wavelength
?
?
electron
proton
 will be
(1)
1
1836
(2) 918
(3) 1 (4) 1836
Answer (4)
Sol. ??
?
e
e
h
mv
??
?
p
p
h
mv
?
? ??
?
p
e
pe
m
1836
m
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
9. The wavelength of the photon emitted by a
hydrogen atom when an electron makes a
transition from n = 2 to n = 1 state is
(1) 490.7 nm (2) 121.8 nm
(3) 913.3 nm (4) 194.8 nm
Answer (2)
Sol.
??
??
??
?
??
22
111
R
12
    
??
??
??
??
3
R
4
? ?? ?
??
7
44
3R
31.0910
         = 121.8 nm
10. For extrinsic semiconductors; when doping
level is increased;
(1) Fermi-level of p-type semiconductors will
go downward and Fermi-level of n-type
semiconductor will go upward.
(2) Fermi-level of p and n-type semiconductors
will not be affected.
(3) Fermi-level of both p-type and n-type
semiconductors will go upward for T > T
F 
K
and downward for T < T
F 
K, where T
F
 is
Fermi temperature.
(4) Fermi-level of p-type semiconductor will go
upward and Fermi-level of n-type
semiconductors will go downward.
Answer (1)
Sol. Fermi-level of p type semiconductor goes down
whereas it goes up for n-type semiconductor.
11. Y = Asin( ?t + ?
0
) is the time-displacement
equation of a SHM. At t = 0 the displacement of
the particle is 
?
A
Y
2
 and it is moving along
negative x-direction. Then the initial phase
angle ?
0
 will be:
(1)
?
6
(2)
? 2
3
(3)
? 5
6
(4)
?
3
Answer (3)
Sol. Draw phasor :
B A
?
?/6 ?/6
At B particle is going toward mean position
? negative x-direction
?
??
5
6
12. The stopping potential for electrons emitted
from a photosensitive surface illuminated by
light of wavelength 491 nm is 0.710 V. When the
incident wavelength is changed to a new value,
the stopping potential is 1.43 V. The new
wavelength is :
(1) 329 nm (2) 400 nm
(3) 382 nm (4) 309 nm
Answer (3)
Sol. ?? ?
?
hc
eV
?? ?
??
12
12
hc hc
eV eV
?? ?
?
2
1240 1240
0.71 1.43
491
??
?
2
1240 1240
0.72
491
?
2
 = 382 nm
13. If a message signal of frequency ‘f
m
’ is
amplitude modulated with a carrier signal of
frequency ‘f
c
’ and radiated through an antenna,
the wavelength of the corresponding signal in
air is:
(1)
c
c
f
(2)
m
c
f
(3)
?
cm
c
ff
(4)
?
cm
c
ff
Answer (1)
Sol.In amplitude modulated wave, wave is
transmitted at frequency of carrier wave
??
c
c
f
14. Given below are two statements :
Statement I : In a diatomic molecule, the
rotational energy at a given
temperature obeys Maxwell’s
distribution.
Statement II : In a diatomic molecule, the
rotational energy at a given
temperature equals the
translational kinetic energy for
each molecule.
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
In the light of the above statements, choose the
correct answer from the options given below:
(1) Both Statement I and Statement II are false.
(2) Statement I is false but Statement II is true.
(3) Statement I is true but Statement II is false.
(4) Both Statement I and Statement II are true.
Answer (3)
Sol. K
R
 = kT
T
3
KkT
2
?
K
T
 for each molecule
3
kT
4
15. A charge ‘q’ is placed at one corner of a cube
as shown in figure. The flux of electrostatic
field 

E
 through the shaded area is:
X
Y
Z
q
(1)
?
0
q
4
(2)
?
0
q
24
(3)
?
0
q
48
(4)
?
0
q
8
Answer (2)
Sol. Complete the cube with double the side with
charge at centre
flux, ?? ? ?
??
00
1qq
38 24
16. An electron with kinetic energy K
1
 enters
between parallel plates of a capacitor at an
angle ‘ ?’ with the plates. It leaves the plates at
angle ‘ ?’ with kinetic energy K
2
. Then the ratio
of kinetic energies K
1
 : K
2
 will be :
(1)
?
?
cos
sin
(2)
?
?
cos
cos
(3)
?
?
2
2
cos
cos
(4)
?
?
2
2
sin
cos
Answer (3)
Sol. v
1
cos ? = v
2
cos ?
?
??
?
2 2
11
22
2
2
Kv cos
K
vcos
v
1
v
2
?
?
17. In a ferromagnetic material, below the curie
temperature, a domain is defined as :
(1) a macroscopic region with randomly
oriented magnetic dipoles.
(2) a macroscopic region with consecutive
magnetic dipoles oriented in opposite
direction.
(3) a macroscopic region with saturation
magnetization.
(4)a macroscopic region with zero
magnetization.
Answer (3)
Sol. Domain is the region in which magnetic
moment is aligned in such a way to produce
saturated magnetization.
18. Two identical springs of spring constant ‘2k’
are attached to a block of mass m and to fixed
support (see figure). When the mass is
displaced from equilibrium position on either
side, it executes simple harmonic motion. The
time period of oscillations of this system is :
2k 2k
m
(1)
?
m
k
(2)
?
m
2k
(3)
?
m
2
2k
(4)
?
m
2
k
Answer (1)
Sol. ??
eq
m
T2
k
?
eq
k4k
??
m
T
k
JEE (MAIN)-2021 Phase-1 (25-02-2021)-E
19. A sphere of radius ‘a’ and mass ‘m’ rolls along
a horizontal plane with constant speed v
0
. It
encounters an inclined plane at angle ? and
climbs upward. Assuming that it rolls without
slipping, how far up the sphere will travel?
a
?
?
0
(1)
2
0
v
5gsin ?
(2)
2
0
v
2gsin ?
(3)
2
0
10v
7gsin ?
(4)
2
0
v 2
5 gsin ?
Answer (3)
Sol. ??
2
T0
17
Kmv
25
?? 
2
0
7
mv mg sin
10
?
?

2
0
7v
10gsin
given answer in official option is 
?
2
0
10v
7gsin
.
20. If e is the electronic charge, c is the speed of
light in free space and h is Planck’s constant,
the quantity 
?? 
2
0
1|e|
4c
 has dimensions of :
(1) [M L T
–1
] (2) [M L T
0
]
(3) [L C
–1
](4)[M
0 
L
0 
T
0
]
Answer (4)
Sol. ?
?
hc
[E]
?
??
2
0
e
[E]
4r
?
?
??
2
00 0
0
e
[M L T ]
4rhc
SECTION - II
Numerical Value Type Questions: This section
contains 10 questions. In Section II, attempt any five
questions out of 10. The answer to each question is a
NUMERICAL VALUE. For each question, enter the
correct numerical value (in decimal notation,
truncated/rounded-off to the second decimal place;
e.g. 06.25, 07.00, –00.33, –00.30, 30.27, –27.30) using
the mouse and the on-screen virtual numeric keypad
in the place designated to enter the answer.
1. The wavelength of an X-ray beam is 10 Å. The
mass of a fictitious particle having the same
energy as that of the X-ray photons is 
x
hkg
3
.
The value of x is _______.
(h = Planck’s constant)
Answer (10)
Sol.
2
hc
Emc ??
?
? ? ? ? ? ??
?
???
–10 8
hh
m
c
10 10 3 10
 = 
10
hkg
3
2. Two identical conducting spheres with
negligible volume have 2.1 nC and –0.1 nC
charges, respectively. They are brought into
contact and then separated by a distance of
0.5 m. The electrostatic force acting between
the spheres is ________ × 10
–9
 N.
?? ?
?
0
9
1
[Given:4 SIunit]
910
Answer (36)
Sol. q ?
1
 = q ?
2
 = 
?
?
12
QQ
1nC
2
12
2
0
qq 1
F.
4
r
??
?
??
 
?
?? ?
–9–9
9
2
10 10
910
(0.5)
= 36 × 10
–9
 N
3. The percentage increase in the speed of
transverse waves produced in a stretched
string if the tension is increased by 4% will be
________%.
Answer (2)
Sol. ?
?
T
v
??
?? ?
v1T
100 100
v2T
 = 2%
4. The peak electric field produced by the
radiation coming from the 8 W bulb at a
distance of 10 m is 
?
?
0
c xV
.
10 m
 The efficiency
of the bulb is 10% and it is a point source. The
value of x is ________.
Answer (2)
Sol.
0
2
0
2
P1
IEc
2
4r
??? ?
?
1
2
0
2
0
P
E
2cr
??
???
??
??
??
2cN
10 C
?
?