JEE Main 2020 Physics September 3 Shift 2 Paper & Solutions | Mock Tests for JEE Main and Advanced 2025 PDF Download

 Page 1


JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 1
Date : 3rd September 2020
Time : 02 : 00 pm - 05 : 00 pm
Subject : Physics
1. A block of mass m attached to a massless spring is performing oscillatory motion of
amplitude ‘A’ on a frictionless horizontal plane. If half of the mass of the block breaks off
when it is passing through its equilibrium point, the amplitude of oscillation for the
remaining system become fA. The value of f is :
(1) 
1
2
(2) 
1
2
(3) 1 (4) 2
Sol. 4
1 max
V V A ? ? ?
m
m
m
m
A
A'
2 max
V V A ' ' ? ? ?
A ? = A’ ?’
k 2k
A A'
m m
?
A’ = 
2
A
2. The mass density of a planet of radius R varies with the distance r from its centre as ?(r)
= ?
0 
2
2
r
1
R
? ?
?
? ?
? ?
. Then the gravitational field is maximum at :
(1) r = 
1
3
R (2) r = 
3
4
R (3) r = R (4) r = 
5
9
R
Sol. 4
dr
r
Page 2


JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 1
Date : 3rd September 2020
Time : 02 : 00 pm - 05 : 00 pm
Subject : Physics
1. A block of mass m attached to a massless spring is performing oscillatory motion of
amplitude ‘A’ on a frictionless horizontal plane. If half of the mass of the block breaks off
when it is passing through its equilibrium point, the amplitude of oscillation for the
remaining system become fA. The value of f is :
(1) 
1
2
(2) 
1
2
(3) 1 (4) 2
Sol. 4
1 max
V V A ? ? ?
m
m
m
m
A
A'
2 max
V V A ' ' ? ? ?
A ? = A’ ?’
k 2k
A A'
m m
?
A’ = 
2
A
2. The mass density of a planet of radius R varies with the distance r from its centre as ?(r)
= ?
0 
2
2
r
1
R
? ?
?
? ?
? ?
. Then the gravitational field is maximum at :
(1) r = 
1
3
R (2) r = 
3
4
R (3) r = R (4) r = 
5
9
R
Sol. 4
dr
r
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 2
dm dv ? ?
2
2
0 2
r
dm 1 4 r dr
R
? ?
? ? ? ?
? ?
? ?
? ?
3 5
0 2
r r
M 4
3 5R
? ?
? ? ? ?
? ?
? ?
g 2
GM
E
r
?
3
g 0 2
r r
E G4
3 5R
? ?
? ? ? ?
? ?
? ?
2
g
2
dE
1 3r
0
dr 3 5R
? ? ?
2
2
1 3 r
3 5 R
?
5
r R
9
?
3. Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm,
respectively. Both the sources emit light of the same power 200 W. The ratio of the number
density of photons of X-rays to the number density of photons of the visible light of the
given wavelengths is :
(1) 
1
500
(2) 
1
250
(3) 500 (4) 250
Sol. 1
nhc
P
t
?
?
n
const ?
?
1 1
2 2
n 1nm 1
n 500nm 500
?
? ? ?
?
4. If a semiconductor photodiode can detect a photon with a maximum wavelength of 400
nm, then its band gap energy is :
Planck’s constant h = 6.63 × 10
–34
 J.s. Speed of light c = 3 × 10
8
 m/s
(1) 1.5 eV (2) 2.0 eV (3) 3.1 eV (4) 1.1 eV
Page 3


JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 1
Date : 3rd September 2020
Time : 02 : 00 pm - 05 : 00 pm
Subject : Physics
1. A block of mass m attached to a massless spring is performing oscillatory motion of
amplitude ‘A’ on a frictionless horizontal plane. If half of the mass of the block breaks off
when it is passing through its equilibrium point, the amplitude of oscillation for the
remaining system become fA. The value of f is :
(1) 
1
2
(2) 
1
2
(3) 1 (4) 2
Sol. 4
1 max
V V A ? ? ?
m
m
m
m
A
A'
2 max
V V A ' ' ? ? ?
A ? = A’ ?’
k 2k
A A'
m m
?
A’ = 
2
A
2. The mass density of a planet of radius R varies with the distance r from its centre as ?(r)
= ?
0 
2
2
r
1
R
? ?
?
? ?
? ?
. Then the gravitational field is maximum at :
(1) r = 
1
3
R (2) r = 
3
4
R (3) r = R (4) r = 
5
9
R
Sol. 4
dr
r
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 2
dm dv ? ?
2
2
0 2
r
dm 1 4 r dr
R
? ?
? ? ? ?
? ?
? ?
? ?
3 5
0 2
r r
M 4
3 5R
? ?
? ? ? ?
? ?
? ?
g 2
GM
E
r
?
3
g 0 2
r r
E G4
3 5R
? ?
? ? ? ?
? ?
? ?
2
g
2
dE
1 3r
0
dr 3 5R
? ? ?
2
2
1 3 r
3 5 R
?
5
r R
9
?
3. Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm,
respectively. Both the sources emit light of the same power 200 W. The ratio of the number
density of photons of X-rays to the number density of photons of the visible light of the
given wavelengths is :
(1) 
1
500
(2) 
1
250
(3) 500 (4) 250
Sol. 1
nhc
P
t
?
?
n
const ?
?
1 1
2 2
n 1nm 1
n 500nm 500
?
? ? ?
?
4. If a semiconductor photodiode can detect a photon with a maximum wavelength of 400
nm, then its band gap energy is :
Planck’s constant h = 6.63 × 10
–34
 J.s. Speed of light c = 3 × 10
8
 m/s
(1) 1.5 eV (2) 2.0 eV (3) 3.1 eV (4) 1.1 eV
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 3
Sol. 3
hc
E ?
?
34 8
9
6.63 10 3 10
E
400 10
?
?
? ? ?
?
?
1240
E eV
400
?
E = 3.1 eV
5. Amount of solar energy received on the earth’s surface per unit area per unit time is
defined a solar constant. Dimension of solar constant is :
(1) ML
0
T
–3
(2) MLT
–2
(3) M
2
L
0
T
–1
(4) ML
2
T
–2
Sol. 1
Q
E
At
?
2 2
2
ML T
E
L T
?
?
E = MT
-3
6. A particle is moving unidirectionally on a horizontal plane under the action of a constant
power supplying energy source. The displacement (s) - time (t) graph that describes the
motion of the particle is (graphs are drawn schematically and are not to scale) :
(1) (2) 
(3) (4) 
Sol. 2
P = FV
dv
P m v
dt
?
P
vdv dt
m
?
2
V k 't ?
V k '' t ?
3/2
s  t ?
Page 4


JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 1
Date : 3rd September 2020
Time : 02 : 00 pm - 05 : 00 pm
Subject : Physics
1. A block of mass m attached to a massless spring is performing oscillatory motion of
amplitude ‘A’ on a frictionless horizontal plane. If half of the mass of the block breaks off
when it is passing through its equilibrium point, the amplitude of oscillation for the
remaining system become fA. The value of f is :
(1) 
1
2
(2) 
1
2
(3) 1 (4) 2
Sol. 4
1 max
V V A ? ? ?
m
m
m
m
A
A'
2 max
V V A ' ' ? ? ?
A ? = A’ ?’
k 2k
A A'
m m
?
A’ = 
2
A
2. The mass density of a planet of radius R varies with the distance r from its centre as ?(r)
= ?
0 
2
2
r
1
R
? ?
?
? ?
? ?
. Then the gravitational field is maximum at :
(1) r = 
1
3
R (2) r = 
3
4
R (3) r = R (4) r = 
5
9
R
Sol. 4
dr
r
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 2
dm dv ? ?
2
2
0 2
r
dm 1 4 r dr
R
? ?
? ? ? ?
? ?
? ?
? ?
3 5
0 2
r r
M 4
3 5R
? ?
? ? ? ?
? ?
? ?
g 2
GM
E
r
?
3
g 0 2
r r
E G4
3 5R
? ?
? ? ? ?
? ?
? ?
2
g
2
dE
1 3r
0
dr 3 5R
? ? ?
2
2
1 3 r
3 5 R
?
5
r R
9
?
3. Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm,
respectively. Both the sources emit light of the same power 200 W. The ratio of the number
density of photons of X-rays to the number density of photons of the visible light of the
given wavelengths is :
(1) 
1
500
(2) 
1
250
(3) 500 (4) 250
Sol. 1
nhc
P
t
?
?
n
const ?
?
1 1
2 2
n 1nm 1
n 500nm 500
?
? ? ?
?
4. If a semiconductor photodiode can detect a photon with a maximum wavelength of 400
nm, then its band gap energy is :
Planck’s constant h = 6.63 × 10
–34
 J.s. Speed of light c = 3 × 10
8
 m/s
(1) 1.5 eV (2) 2.0 eV (3) 3.1 eV (4) 1.1 eV
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 3
Sol. 3
hc
E ?
?
34 8
9
6.63 10 3 10
E
400 10
?
?
? ? ?
?
?
1240
E eV
400
?
E = 3.1 eV
5. Amount of solar energy received on the earth’s surface per unit area per unit time is
defined a solar constant. Dimension of solar constant is :
(1) ML
0
T
–3
(2) MLT
–2
(3) M
2
L
0
T
–1
(4) ML
2
T
–2
Sol. 1
Q
E
At
?
2 2
2
ML T
E
L T
?
?
E = MT
-3
6. A particle is moving unidirectionally on a horizontal plane under the action of a constant
power supplying energy source. The displacement (s) - time (t) graph that describes the
motion of the particle is (graphs are drawn schematically and are not to scale) :
(1) (2) 
(3) (4) 
Sol. 2
P = FV
dv
P m v
dt
?
P
vdv dt
m
?
2
V k 't ?
V k '' t ?
3/2
s  t ?
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 4
7. Which of the following will NOT be observed when a multimeter (operating in resistance
measuring mode) probes connected across a component, are just reversed ?
(1) Multimeter shows NO deflection in both cases i.e. before and after reversing the
probes if the chosen component is metal wire.
(2) Multimeter shows a deflection, accompanied by a splash of light out of connected
component in one direction and NO deflection on reversing the probes if the chosen
component is LED.
(3) Multimeter shows an equal deflection in both cases i.e. before and after reversing
the probes if  the chosen component is resistor.
(4) Multimeter shows NO deflection in both cases i.e. before and after reversing the
probes if the chosen component is capacitor.
Sol. 4
By Theory
8. A uniform rod of length ‘l’ is pivoted at one of its ends on a vertical shaft of negligible
radius. When the shaft rotates at angular speed ? the rod makes an angle ? with it (see
figure). To find ? equate the rate of change of angular momentum (direction going into
the paper) 
2
ml
12
?
2 
sin ? cos ? ?about the centre of mass (CM) to the torque provided by the
horizontal and vertical forces F
H
 and F
V
 about the CM. The value of ? is then such that :
(1) cos ? = 
2
2g
3l ?
(2) cos ? =
2
3g
2l ?
(3) cos ? =
2
g
2l ?
(4) cos ? = 
2
g
l ?
Sol. 2
F
V
F
H
Mg
F
V
 = mg
Page 5


JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 1
Date : 3rd September 2020
Time : 02 : 00 pm - 05 : 00 pm
Subject : Physics
1. A block of mass m attached to a massless spring is performing oscillatory motion of
amplitude ‘A’ on a frictionless horizontal plane. If half of the mass of the block breaks off
when it is passing through its equilibrium point, the amplitude of oscillation for the
remaining system become fA. The value of f is :
(1) 
1
2
(2) 
1
2
(3) 1 (4) 2
Sol. 4
1 max
V V A ? ? ?
m
m
m
m
A
A'
2 max
V V A ' ' ? ? ?
A ? = A’ ?’
k 2k
A A'
m m
?
A’ = 
2
A
2. The mass density of a planet of radius R varies with the distance r from its centre as ?(r)
= ?
0 
2
2
r
1
R
? ?
?
? ?
? ?
. Then the gravitational field is maximum at :
(1) r = 
1
3
R (2) r = 
3
4
R (3) r = R (4) r = 
5
9
R
Sol. 4
dr
r
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 2
dm dv ? ?
2
2
0 2
r
dm 1 4 r dr
R
? ?
? ? ? ?
? ?
? ?
? ?
3 5
0 2
r r
M 4
3 5R
? ?
? ? ? ?
? ?
? ?
g 2
GM
E
r
?
3
g 0 2
r r
E G4
3 5R
? ?
? ? ? ?
? ?
? ?
2
g
2
dE
1 3r
0
dr 3 5R
? ? ?
2
2
1 3 r
3 5 R
?
5
r R
9
?
3. Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm,
respectively. Both the sources emit light of the same power 200 W. The ratio of the number
density of photons of X-rays to the number density of photons of the visible light of the
given wavelengths is :
(1) 
1
500
(2) 
1
250
(3) 500 (4) 250
Sol. 1
nhc
P
t
?
?
n
const ?
?
1 1
2 2
n 1nm 1
n 500nm 500
?
? ? ?
?
4. If a semiconductor photodiode can detect a photon with a maximum wavelength of 400
nm, then its band gap energy is :
Planck’s constant h = 6.63 × 10
–34
 J.s. Speed of light c = 3 × 10
8
 m/s
(1) 1.5 eV (2) 2.0 eV (3) 3.1 eV (4) 1.1 eV
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 3
Sol. 3
hc
E ?
?
34 8
9
6.63 10 3 10
E
400 10
?
?
? ? ?
?
?
1240
E eV
400
?
E = 3.1 eV
5. Amount of solar energy received on the earth’s surface per unit area per unit time is
defined a solar constant. Dimension of solar constant is :
(1) ML
0
T
–3
(2) MLT
–2
(3) M
2
L
0
T
–1
(4) ML
2
T
–2
Sol. 1
Q
E
At
?
2 2
2
ML T
E
L T
?
?
E = MT
-3
6. A particle is moving unidirectionally on a horizontal plane under the action of a constant
power supplying energy source. The displacement (s) - time (t) graph that describes the
motion of the particle is (graphs are drawn schematically and are not to scale) :
(1) (2) 
(3) (4) 
Sol. 2
P = FV
dv
P m v
dt
?
P
vdv dt
m
?
2
V k 't ?
V k '' t ?
3/2
s  t ?
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 4
7. Which of the following will NOT be observed when a multimeter (operating in resistance
measuring mode) probes connected across a component, are just reversed ?
(1) Multimeter shows NO deflection in both cases i.e. before and after reversing the
probes if the chosen component is metal wire.
(2) Multimeter shows a deflection, accompanied by a splash of light out of connected
component in one direction and NO deflection on reversing the probes if the chosen
component is LED.
(3) Multimeter shows an equal deflection in both cases i.e. before and after reversing
the probes if  the chosen component is resistor.
(4) Multimeter shows NO deflection in both cases i.e. before and after reversing the
probes if the chosen component is capacitor.
Sol. 4
By Theory
8. A uniform rod of length ‘l’ is pivoted at one of its ends on a vertical shaft of negligible
radius. When the shaft rotates at angular speed ? the rod makes an angle ? with it (see
figure). To find ? equate the rate of change of angular momentum (direction going into
the paper) 
2
ml
12
?
2 
sin ? cos ? ?about the centre of mass (CM) to the torque provided by the
horizontal and vertical forces F
H
 and F
V
 about the CM. The value of ? is then such that :
(1) cos ? = 
2
2g
3l ?
(2) cos ? =
2
3g
2l ?
(3) cos ? =
2
g
2l ?
(4) cos ? = 
2
g
l ?
Sol. 2
F
V
F
H
Mg
F
V
 = mg
JEE Main 2020 Paper
         3
rd
 September 2020 | (Shift-2), Physics     Page | 5
F
H
 = 
2
m sin
2
? ?
?
?
net
? about COM = 
V H
F . sin F cos
2 2
? ? ?
? ?
= 
2
2
m
sin cos
12
? ? ?
?
? ? ? ?
2
2 2
mg sin m sin cos m sin cos
2 2 2 12
? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ?
? ? ? ? ? ?
? ?
? ? ? ?
2 2 2
2
g
cos cos
2 4 12
?
? ? ? ? ? ?
? ? ?
2 2
g 1 1
cos
2 12 4
? ?
? ? ? ?
? ?
? ?
?
?
2 2
g cos
2 3
? ?
?
? ?
2
g
cos
2
?
? ?
? ?
9. Two resistors 400 ? and 800 ? are connected in series across a 6 V battery. The potential
difference measured by a voltmeter of 10 k ? across 400 ? resistor is close to :
(1) 2.05 V (2) 2 V (3) 1.95 V (4) 1.8 V
Sol. 3
i
1
6V
i
voltmeter
6
i
400 10000
800
400 10000
?
?
?
?
6
i
40000
800
10400
?
?
6 6
i 0.00506
800 384.61 1184.61
? ? ?
?
v
V 6 800 0.00506 6 4.05 1.95 ? ? ? ? ? ?