JEE Mains 25 Feb 2021 Question Paper Shift 1 | JEE Main & Advanced Previous Year Papers PDF Download

 Page 1


 
 
Section - A 
1. A 5V battery is connected across the points X and Y. Assume D
1 
and D
2
 to be normal silicon 
diodes. Find the current supplied by the battery if the +ve terminal of the battery is connected 
to point X.  
 
10 ?
D
1
5 ? D
2
x y
 
(1) ~0.86 A  (2) ~0.5 A  (3) ~ 0.43 A  (4)~ 1.5 A 
Sol. 3 
Since silicon diode is used so 0.7 Volt is drop across it, only D
1
 will conduct so current through cell  
5 0.7
I
10
?
? = 0.43 A  
 
2. A solid sphere of radius R gravitationally attracts a particle placed at 3R from its centre with a 
force F
1
. Now a spherical cavity of radius 
R
2
? ?
? ?
? ?
 is made in the sphere (as shown in figure) and 
the force becomes F
2
. The value of F
1
 : F
2
 is :  
 
 
(1)41 : 50 (2) 36 : 25 (3) 50 : 41 (4) 25 : 36 
Sol. 1 
 g
1
 = 
2 2
GM GM
(3R) 9R
? 
 g
2
 = 
2 2
M
G
8 GM
9R
R
3R
2
? ?
? ?
? ?
?
? ?
?
? ?
? ?
 
 
2 2 2
GM GM 41 GM
9 50
9R R 50 R
? ? ?
?
 
 
1
2
g 41
g 50
? 
 Force ?
1 1
2 2
F mg 41
F mg 50
? ? 
B 
2R 
 A 
m 
 M 
 O 
25
th
 Feb. 2021 | Shift - 1
PHYSICS
Page 2


 
 
Section - A 
1. A 5V battery is connected across the points X and Y. Assume D
1 
and D
2
 to be normal silicon 
diodes. Find the current supplied by the battery if the +ve terminal of the battery is connected 
to point X.  
 
10 ?
D
1
5 ? D
2
x y
 
(1) ~0.86 A  (2) ~0.5 A  (3) ~ 0.43 A  (4)~ 1.5 A 
Sol. 3 
Since silicon diode is used so 0.7 Volt is drop across it, only D
1
 will conduct so current through cell  
5 0.7
I
10
?
? = 0.43 A  
 
2. A solid sphere of radius R gravitationally attracts a particle placed at 3R from its centre with a 
force F
1
. Now a spherical cavity of radius 
R
2
? ?
? ?
? ?
 is made in the sphere (as shown in figure) and 
the force becomes F
2
. The value of F
1
 : F
2
 is :  
 
 
(1)41 : 50 (2) 36 : 25 (3) 50 : 41 (4) 25 : 36 
Sol. 1 
 g
1
 = 
2 2
GM GM
(3R) 9R
? 
 g
2
 = 
2 2
M
G
8 GM
9R
R
3R
2
? ?
? ?
? ?
?
? ?
?
? ?
? ?
 
 
2 2 2
GM GM 41 GM
9 50
9R R 50 R
? ? ?
?
 
 
1
2
g 41
g 50
? 
 Force ?
1 1
2 2
F mg 41
F mg 50
? ? 
B 
2R 
 A 
m 
 M 
 O 
25
th
 Feb. 2021 | Shift - 1
PHYSICS
 
 
3. A student is performing the experiment of resonance column. The diameter of the column tube 
is 6 cm. The frequency of the tuning fork is 504 Hz. Speed of the sound at the given 
temperature is 336 m/s. The zero of the metre scale coincides with the top end of the 
resonance column tube. The reading of the water level in the column when the first resonance 
occurs is :  
(1) 13 cm  (2) 14.8 cm (3) 16.6 cm (4) 18.4 cm   
Sol. 2 
 
v 336
f 504
? ? ? = 66.66cm  
 
4
?
 = l + e = l + 0.3d  
 = l + 1.8 
 16.66 = l + 1.8 cm  
 l = 14.86 cm  
 
4. A diatomic gas, having 
p
7
C R
2
? and 
v
5
C R,
2
? is heated at constant pressure.  
 The ratio dU : dQ : dW 
(1) 3 : 7 : 2  (2) 5 : 7 : 2  (3) 5 : 7 : 3  (4) 3 : 5 : 2 
Sol. 2 
 C
p
 = 
7
2
 R 
 C
v
 = 
5
2
 R 
 dU = nC
v
dT 
 dQ = nC
p
dT 
 dW = nRdT 
 dU : dQ : dW  
 C
v
 : C
p
 : R 
 
5
2
R :
7
2
 R : R  
 5 : 7 : 2  
 
5. Given below are two statements : 
Statement I : A speech signal of 2 kHz is used to modulate a carrier signal of 1 MHz. The 
bandwidth requirement for the signal is 4 kHz.  
Statement II : The side band frequencies are 1002 kHz and 998 kHz.  
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  
Page 3


 
 
Section - A 
1. A 5V battery is connected across the points X and Y. Assume D
1 
and D
2
 to be normal silicon 
diodes. Find the current supplied by the battery if the +ve terminal of the battery is connected 
to point X.  
 
10 ?
D
1
5 ? D
2
x y
 
(1) ~0.86 A  (2) ~0.5 A  (3) ~ 0.43 A  (4)~ 1.5 A 
Sol. 3 
Since silicon diode is used so 0.7 Volt is drop across it, only D
1
 will conduct so current through cell  
5 0.7
I
10
?
? = 0.43 A  
 
2. A solid sphere of radius R gravitationally attracts a particle placed at 3R from its centre with a 
force F
1
. Now a spherical cavity of radius 
R
2
? ?
? ?
? ?
 is made in the sphere (as shown in figure) and 
the force becomes F
2
. The value of F
1
 : F
2
 is :  
 
 
(1)41 : 50 (2) 36 : 25 (3) 50 : 41 (4) 25 : 36 
Sol. 1 
 g
1
 = 
2 2
GM GM
(3R) 9R
? 
 g
2
 = 
2 2
M
G
8 GM
9R
R
3R
2
? ?
? ?
? ?
?
? ?
?
? ?
? ?
 
 
2 2 2
GM GM 41 GM
9 50
9R R 50 R
? ? ?
?
 
 
1
2
g 41
g 50
? 
 Force ?
1 1
2 2
F mg 41
F mg 50
? ? 
B 
2R 
 A 
m 
 M 
 O 
25
th
 Feb. 2021 | Shift - 1
PHYSICS
 
 
3. A student is performing the experiment of resonance column. The diameter of the column tube 
is 6 cm. The frequency of the tuning fork is 504 Hz. Speed of the sound at the given 
temperature is 336 m/s. The zero of the metre scale coincides with the top end of the 
resonance column tube. The reading of the water level in the column when the first resonance 
occurs is :  
(1) 13 cm  (2) 14.8 cm (3) 16.6 cm (4) 18.4 cm   
Sol. 2 
 
v 336
f 504
? ? ? = 66.66cm  
 
4
?
 = l + e = l + 0.3d  
 = l + 1.8 
 16.66 = l + 1.8 cm  
 l = 14.86 cm  
 
4. A diatomic gas, having 
p
7
C R
2
? and 
v
5
C R,
2
? is heated at constant pressure.  
 The ratio dU : dQ : dW 
(1) 3 : 7 : 2  (2) 5 : 7 : 2  (3) 5 : 7 : 3  (4) 3 : 5 : 2 
Sol. 2 
 C
p
 = 
7
2
 R 
 C
v
 = 
5
2
 R 
 dU = nC
v
dT 
 dQ = nC
p
dT 
 dW = nRdT 
 dU : dQ : dW  
 C
v
 : C
p
 : R 
 
5
2
R :
7
2
 R : R  
 5 : 7 : 2  
 
5. Given below are two statements : 
Statement I : A speech signal of 2 kHz is used to modulate a carrier signal of 1 MHz. The 
bandwidth requirement for the signal is 4 kHz.  
Statement II : The side band frequencies are 1002 kHz and 998 kHz.  
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  
 
 
Sol. 4 
 Side band = (f
c
 - f
m
) to (f
c
 + f
m
) 
 = (1000 – 2) KHz to (1000 + 2) KHz
 
 
= 998 KHz to 1002 kHz
 
 
Band width = 2f
m
 
 = 2 ×2 KHz
 
 
= 4 KHz 
 Both statements are true   
 
6. The current (i) at time t=0 and t = ? respectively for the given circuit is : 
 
^i 
 
5 ? 5 ?
4 ?
1 ?
L 
? ?
 
 (1) 
18E 5E
,
55 18
 (2) 
5E 18E
,
18 55
 (3) 
5E 10E
,
18 33
 (4) 
10E 5E
,
33 18
 
 
Sol. 3 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 at t = 0, inductor is removed, so circuit will look like this 
 at t =  0 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 R
eq
 = 
6 9
6 9
?
?
 = 
54
15
 
 I (t = 0) = 
E 15
54
?
 = 
5E
18
 
Page 4


 
 
Section - A 
1. A 5V battery is connected across the points X and Y. Assume D
1 
and D
2
 to be normal silicon 
diodes. Find the current supplied by the battery if the +ve terminal of the battery is connected 
to point X.  
 
10 ?
D
1
5 ? D
2
x y
 
(1) ~0.86 A  (2) ~0.5 A  (3) ~ 0.43 A  (4)~ 1.5 A 
Sol. 3 
Since silicon diode is used so 0.7 Volt is drop across it, only D
1
 will conduct so current through cell  
5 0.7
I
10
?
? = 0.43 A  
 
2. A solid sphere of radius R gravitationally attracts a particle placed at 3R from its centre with a 
force F
1
. Now a spherical cavity of radius 
R
2
? ?
? ?
? ?
 is made in the sphere (as shown in figure) and 
the force becomes F
2
. The value of F
1
 : F
2
 is :  
 
 
(1)41 : 50 (2) 36 : 25 (3) 50 : 41 (4) 25 : 36 
Sol. 1 
 g
1
 = 
2 2
GM GM
(3R) 9R
? 
 g
2
 = 
2 2
M
G
8 GM
9R
R
3R
2
? ?
? ?
? ?
?
? ?
?
? ?
? ?
 
 
2 2 2
GM GM 41 GM
9 50
9R R 50 R
? ? ?
?
 
 
1
2
g 41
g 50
? 
 Force ?
1 1
2 2
F mg 41
F mg 50
? ? 
B 
2R 
 A 
m 
 M 
 O 
25
th
 Feb. 2021 | Shift - 1
PHYSICS
 
 
3. A student is performing the experiment of resonance column. The diameter of the column tube 
is 6 cm. The frequency of the tuning fork is 504 Hz. Speed of the sound at the given 
temperature is 336 m/s. The zero of the metre scale coincides with the top end of the 
resonance column tube. The reading of the water level in the column when the first resonance 
occurs is :  
(1) 13 cm  (2) 14.8 cm (3) 16.6 cm (4) 18.4 cm   
Sol. 2 
 
v 336
f 504
? ? ? = 66.66cm  
 
4
?
 = l + e = l + 0.3d  
 = l + 1.8 
 16.66 = l + 1.8 cm  
 l = 14.86 cm  
 
4. A diatomic gas, having 
p
7
C R
2
? and 
v
5
C R,
2
? is heated at constant pressure.  
 The ratio dU : dQ : dW 
(1) 3 : 7 : 2  (2) 5 : 7 : 2  (3) 5 : 7 : 3  (4) 3 : 5 : 2 
Sol. 2 
 C
p
 = 
7
2
 R 
 C
v
 = 
5
2
 R 
 dU = nC
v
dT 
 dQ = nC
p
dT 
 dW = nRdT 
 dU : dQ : dW  
 C
v
 : C
p
 : R 
 
5
2
R :
7
2
 R : R  
 5 : 7 : 2  
 
5. Given below are two statements : 
Statement I : A speech signal of 2 kHz is used to modulate a carrier signal of 1 MHz. The 
bandwidth requirement for the signal is 4 kHz.  
Statement II : The side band frequencies are 1002 kHz and 998 kHz.  
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  
 
 
Sol. 4 
 Side band = (f
c
 - f
m
) to (f
c
 + f
m
) 
 = (1000 – 2) KHz to (1000 + 2) KHz
 
 
= 998 KHz to 1002 kHz
 
 
Band width = 2f
m
 
 = 2 ×2 KHz
 
 
= 4 KHz 
 Both statements are true   
 
6. The current (i) at time t=0 and t = ? respectively for the given circuit is : 
 
^i 
 
5 ? 5 ?
4 ?
1 ?
L 
? ?
 
 (1) 
18E 5E
,
55 18
 (2) 
5E 18E
,
18 55
 (3) 
5E 10E
,
18 33
 (4) 
10E 5E
,
33 18
 
 
Sol. 3 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 at t = 0, inductor is removed, so circuit will look like this 
 at t =  0 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 R
eq
 = 
6 9
6 9
?
?
 = 
54
15
 
 I (t = 0) = 
E 15
54
?
 = 
5E
18
 
 
 
 at t = ?, inductor is replaced by plane wire, so circuit will look like this 
 at t = ? 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 I (t = ?) = 
E
5 4
2 5
?
 = 
10E
33
 
 Now, 
 
 
5 ? 
I
E
4 ? 1 ? 
5 ? 
 
 R
eq
 = 
1 4
1 4
?
?
 + 
5 5
5 5
?
?
 
 = 
4
5
 + 
5
2
 = 
8 25
10
?
 = 
33
10
 
 I = 
eq
E
R
 = 
10E
33
 
 
7. Two satellites A and B of masses 200 kg and 400 kg are revolving round the earth at height of 
600 km and 1600 km respectively.  
 If T
A
 and T
B
 are the time periods of A and B respectively then the value of T
B
 – T
A
 : 
 
 
B 
 E 
A 
 
 [Given : radius of earth = 6400 km, mass of earth = 6× 10
24
 kg] 
 (1) 4.24× 10
2
 s (2) 3.33 × 10
2
 s (3) 1.33 × 10
3
 s (4) 4.24 × 10
3
 s 
Page 5


 
 
Section - A 
1. A 5V battery is connected across the points X and Y. Assume D
1 
and D
2
 to be normal silicon 
diodes. Find the current supplied by the battery if the +ve terminal of the battery is connected 
to point X.  
 
10 ?
D
1
5 ? D
2
x y
 
(1) ~0.86 A  (2) ~0.5 A  (3) ~ 0.43 A  (4)~ 1.5 A 
Sol. 3 
Since silicon diode is used so 0.7 Volt is drop across it, only D
1
 will conduct so current through cell  
5 0.7
I
10
?
? = 0.43 A  
 
2. A solid sphere of radius R gravitationally attracts a particle placed at 3R from its centre with a 
force F
1
. Now a spherical cavity of radius 
R
2
? ?
? ?
? ?
 is made in the sphere (as shown in figure) and 
the force becomes F
2
. The value of F
1
 : F
2
 is :  
 
 
(1)41 : 50 (2) 36 : 25 (3) 50 : 41 (4) 25 : 36 
Sol. 1 
 g
1
 = 
2 2
GM GM
(3R) 9R
? 
 g
2
 = 
2 2
M
G
8 GM
9R
R
3R
2
? ?
? ?
? ?
?
? ?
?
? ?
? ?
 
 
2 2 2
GM GM 41 GM
9 50
9R R 50 R
? ? ?
?
 
 
1
2
g 41
g 50
? 
 Force ?
1 1
2 2
F mg 41
F mg 50
? ? 
B 
2R 
 A 
m 
 M 
 O 
25
th
 Feb. 2021 | Shift - 1
PHYSICS
 
 
3. A student is performing the experiment of resonance column. The diameter of the column tube 
is 6 cm. The frequency of the tuning fork is 504 Hz. Speed of the sound at the given 
temperature is 336 m/s. The zero of the metre scale coincides with the top end of the 
resonance column tube. The reading of the water level in the column when the first resonance 
occurs is :  
(1) 13 cm  (2) 14.8 cm (3) 16.6 cm (4) 18.4 cm   
Sol. 2 
 
v 336
f 504
? ? ? = 66.66cm  
 
4
?
 = l + e = l + 0.3d  
 = l + 1.8 
 16.66 = l + 1.8 cm  
 l = 14.86 cm  
 
4. A diatomic gas, having 
p
7
C R
2
? and 
v
5
C R,
2
? is heated at constant pressure.  
 The ratio dU : dQ : dW 
(1) 3 : 7 : 2  (2) 5 : 7 : 2  (3) 5 : 7 : 3  (4) 3 : 5 : 2 
Sol. 2 
 C
p
 = 
7
2
 R 
 C
v
 = 
5
2
 R 
 dU = nC
v
dT 
 dQ = nC
p
dT 
 dW = nRdT 
 dU : dQ : dW  
 C
v
 : C
p
 : R 
 
5
2
R :
7
2
 R : R  
 5 : 7 : 2  
 
5. Given below are two statements : 
Statement I : A speech signal of 2 kHz is used to modulate a carrier signal of 1 MHz. The 
bandwidth requirement for the signal is 4 kHz.  
Statement II : The side band frequencies are 1002 kHz and 998 kHz.  
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  
 
 
Sol. 4 
 Side band = (f
c
 - f
m
) to (f
c
 + f
m
) 
 = (1000 – 2) KHz to (1000 + 2) KHz
 
 
= 998 KHz to 1002 kHz
 
 
Band width = 2f
m
 
 = 2 ×2 KHz
 
 
= 4 KHz 
 Both statements are true   
 
6. The current (i) at time t=0 and t = ? respectively for the given circuit is : 
 
^i 
 
5 ? 5 ?
4 ?
1 ?
L 
? ?
 
 (1) 
18E 5E
,
55 18
 (2) 
5E 18E
,
18 55
 (3) 
5E 10E
,
18 33
 (4) 
10E 5E
,
33 18
 
 
Sol. 3 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 at t = 0, inductor is removed, so circuit will look like this 
 at t =  0 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 R
eq
 = 
6 9
6 9
?
?
 = 
54
15
 
 I (t = 0) = 
E 15
54
?
 = 
5E
18
 
 
 
 at t = ?, inductor is replaced by plane wire, so circuit will look like this 
 at t = ? 
 
 5 ? 5 ?
I
E
1 ? 4 ?
 
 I (t = ?) = 
E
5 4
2 5
?
 = 
10E
33
 
 Now, 
 
 
5 ? 
I
E
4 ? 1 ? 
5 ? 
 
 R
eq
 = 
1 4
1 4
?
?
 + 
5 5
5 5
?
?
 
 = 
4
5
 + 
5
2
 = 
8 25
10
?
 = 
33
10
 
 I = 
eq
E
R
 = 
10E
33
 
 
7. Two satellites A and B of masses 200 kg and 400 kg are revolving round the earth at height of 
600 km and 1600 km respectively.  
 If T
A
 and T
B
 are the time periods of A and B respectively then the value of T
B
 – T
A
 : 
 
 
B 
 E 
A 
 
 [Given : radius of earth = 6400 km, mass of earth = 6× 10
24
 kg] 
 (1) 4.24× 10
2
 s (2) 3.33 × 10
2
 s (3) 1.33 × 10
3
 s (4) 4.24 × 10
3
 s 
 
 
Sol. 3  
 V = 
e
GM
r
 
 T = 
e
e
2 r r
2 r
GM
GM
r
?
? ?  
 T = 
2 3
e
4 r
GM
?
 = 
2 3
e
4 r
GM
?
 
 T
2
 –T
1 
= 
2 3 3
24
4 (8000 10 )
G 6 10
? ?
? ?
2 3 3
24
4 (7000 10 )
6 10
?
?
? ? G
?
 
 ? 1.33 × 10
3
s 
 
8. An engine of a train, moving with uniform acceleration, passes the signal post with velocity u 
and the last compartment with velocity v. The velocity with which middle point of the train 
passes the signal post is :  
 (1) 
2 2
v u
2
?
 (2) 
v u
2
?
 (3) 
2 2
v u
2
?
 (4) 
u v
2
?
 
Sol. 3  
 
 a
u
l
 
 a = uniform acceleration 
 u = velocity of first compartment 
 v = velocity of last compartment 
 l = length of train 
 v
2
 = u
2
 + 2as (3
rd
 equation of motion) 
 v
2
 = u
2
 + 2al .....(1) 
 v
2
middle
 = u
2
 + 2a 
l
2
 
 ? v
2
middle
 = u
2
 + al  ....(2) 
 from equation (1) and (2) 
 v
2
middle
 = u
2
 + 
2 2
v u
2
? ?
?
? ?
? ?
? ?
 
 = 
2 2
v u
2
?
 
 ?v
middle
 = 
2 2
v u
2
?
 
 
V
r
Me Ms ?