# JEE Main 2021 20th July Shift 1 Physics Question Paper || JEE Main 2021 Physics question paper for July 20th

दोस्तों यहां पर Physics का Solved Paper दिया गया है तथा आपको JEE Main का ऑनलाइन टेस्ट भी इस वेबसाइट पर दिया गया है।

 Section A

1. The radiation corresponding to 3 → 2 transition of a hydrogen atom falls on a gold surface to generate photoelectrons. These electrons are passed through a magnetic field of 5 x 10⁴ T. Assume that the radius of the largest circular path followed by these electrons is 7 mm, the work function of the metal is : (Mass of electron = 9.1 x 10³¹ kg)

(1) 0.82 eV
(2) 0.16 eV
(3) 1.88 eV
(4) 1.36 eV

(1) 0.82 eV

2. If and are two vectors satisfying the relation . = [ x ]. Then the value of [ ] will be :

(1)

3. The value of current in the 6Ω resistance is :

(1) 4 A
(2) 6 A
(3) 8 A
(4) 10 A

(4) 10 A

4. A deuteron and an alpha particle having equal kinetic energy enter perpendicular into a magnetic field. Let rd and rα be their respective radii of circular path. The value of ta is rd/rα equal to

(1) √2
(2) 1
(3) 2
(4) 1/√2

(1) √2

5. A radioactive material decays by simultaneous emissions of two particles with half lives of 1400 years and 700 years respectively. What will be the time after which one-third of the material remains ? (Take In3 = 1.1)

(1) 1110 years
(2) 340 years
(3) 740 years
(4) 700 years

(3) 740 years

6. A person whose mass is 100 kg travels from Earth to Mars in a spaceship. Neglect all other objects in sky and take acceleration due to gravity on the surface of the Earth and Mars as 10 m/s² and 4 m/s² respectively. Identify from the below figures, the curve that fits best for the weight of the passenger as a function of time.
(1) b
(2) a
(3) x
(4) d

(3) C

7. The amount of heat needed to raise the temperature of 4 moles of a rigid diatomic gas from 0°C to 50°C when no work is done is…….. (R is the universal gas constant)

(1) 750 R
(2) 175 R
(3) 500 R
(4) 250 R

(3) 500 R

8. The value of tension in a long thin metal wire has been changed from T₁ to T₂. The lengths of the metal wire at two different values of tension T₁ and T₂ are l₁ and l₂ respectively. The actual length of the metal wire is :

(1)

9. A butterfly is flying with a velocity 4√2 m/s in North-East direction. Wind is slowly blowing at 1 m/s from North to South. The resultant displacement of the butterfly in 3 seconds is :

(1) 15 m
(2) 12 √2 m
(3) 3 m
(4) 20 m

(1) 15 m

10. A certain charge Q is divided into two parts qand (Q-q). How should the charges Q and q be divided so that q and (Q-q) placed at a certain distance apart experience maximum electrostatic repulsion?

(1) Q = q/2
(2) Q = 3q
(3) Q = 2q
(4) Q = 4q

(3) Q = 2q

11. The entropy of any system is given by
Where α and β are the constants μ J, k and R are no. of moles, mechanical equivalent of heat, Boltzmann constant and gas constant respectively. (take S = dQ/T]
Choose the incorrect option from the following:

(1) S, β,k and μR have the same dimensions.
(2) α and J have the same dimensions.
(3) S and α have different dimensions.
(4) α and k have the same dimensions.

(4) α and k have the same dimensions.

12. The arm PQ of a rectangular conductor is moving from x = 0 to x = 2b outwards and then inwards from x = 2b to x = 0 as shown in the figure. A uniform magnetic field perpendicular to the plane is acting from x = 0 to x = b. Identify the graph showing the variation of different quantities with distance.

(1) A-Flux, B-EMF, C-Power dissipated
(2) A-Power dissipated, B-Flux, C-EMF
(3) A-Flux, B-Power, dissipated, C-EMF
(4) A-EMF, B-Power dissipated, C-Flux

(1) A-Flux, B-EMF, C-Power dissipated

13. A steel block of 10 kg rests on a horizontal floor as shown. When three iron cylinders are placed on it as shown, the block and cylinders go down with an acceleration 0.2 m/s². The normal reaction R’ by the floor if mass of the iron cylinders are equal and of 20 kg each, is_______
(take g = 10 m/s² and μ = 0.2]

(1) 714
(2) 716
(3) 684
(4) 686

(4) 686

14. For the circuit shown below, calculate the value of Iz :

(1) 0.15 A
(2) 0.05 A
(3) 0.1 A
(4) 25m A

(4) 25m A

15. A nucleus of mass M emits γ-ray photon of frequency’v’. The loss of internal energy by the nucleus is :

(1) 0
(2)
(3) hv
(4)

(2)

16. Region I and II are separated by a spherical surface of radius 25 cm. An object is kept in region I at a distance of 40 cm from the surface. The distance of the image from the surface is
(1) 55.44 cm
(2) 9.52 cm
(3) 37.58 cm
(4) 18.23 cm

(3) 37.58 cm

17. AC voltage V(t) = 20 sinot of frequency 50 Hz is applied to a parallel plate capacitor. The separation between the plates is 2 mm and the area is 1 m². The amplitude of the oscillating displacement current for the applied AC voltage is________
[take ε = 8.85 x 10¹² F/m]

(1) 21.14 ua
(2) 83.37 ua
(3) 55.58 uA
(4) 27.79 uA

(4) 27.79 uA

18. The normal reaction ‘N’ for a vehicle of 800 kg mass, negotiating a turn on a 30° banked road at maximum possible speed without skidding is_______ x10³ kg m/s²
[Given cos30o = 0.87, μs = 0.2]

(1) 12.4
(2) 7.2
(3) 6.96
(4) 10.2

(4) 10.2

19. A current of 5A is passing through a non-linear magnesium wire of cross-section 0.04m². At every point, the direction of current density is at an angle of 60° with the unit vector of area of cross-section. The magnitude of electric field at every point of the conductor is :
Resistivity of magnesium = 44 x 10⁸2Ωm

(1) 11 x 10³ V/m
(2) 11 x 10⁵ V/m
(3) 11x 10⁷ V/m
(4) 11 x 10² V/m

(2) 11 x 10⁵ V/m

20. Consider a mixture of gas molecule of types A, B and C having masses mA < mB < mC ratio of their root mean square speeds at normal temperature and pressure is :

(4)

 Section B

21. A body having specific charge 8 μC/g is resting on a frictionless plane at a distance 10 cm from the wall (as shown in the figure). It starts moving towards the wall when uniform electric field of 100 V/m is applied horizontally toward the wall. If the collision of the body with the wall is perfectly elastic. then the time period of the motion will be______ s.

1

22. In a spring gun having spring constant 100 N/m a small ball ‘B’ of mass 100 g is put in its barrel (as shown in figure) by compressing the spring through 0.05 m. There should be a box placed at a distance ď on the ground so that the ball falls in it. If the ball leaves the gun horizontally at a height of 2 m above the ground. The value of d is____ m.
(g = 10 m/s²).

1

23. A rod of mass M and length L is lying on a horizontal frictionless surface. A particle of mass ‘m’ travelling along the surface hits at one end of the rod with velocity ‘u’ in a direction perpendicular to the rod. The collision is completely elastic. After collision, particle comes to rest. The ratio of masses
(m/M) is 1/x . the value of ‘x’ will be ………

4

24. An object viewed from a near point distance of 25 cm, using a microscopic lens with magnification ‘6’, gives an unresolved image. A resolved image is observed at infinite distance with a total magnification double the earlier using an eyepiece along with the given lens and a tube of length 0.6 m, if the focal length of the eyepiece is
equal to______ cm.

25. In an LCR series circuit, an inductor 30 mH and a resistor 1 Ω are connected to an AC source of angular frequency 300 rad/s. The value of capacitance for which, the current leads the voltage by 45° is 1/x x 10³ F. Then the value of x is_______

25

26. The frequency of a car horn encountered a change from 400 Hz to 500 Hz, when the car approaches a vertical wall. If the speed of sound is 330 m/s. Then the speed of car is ______ km/h.

132

27. A carrier wave Vc(t) = 160 sin(2π x 10⁶t) volts is made to vary between Vmax = 200 V and Vmin = 120 V by a message signal Vm(t) = Am sin(2π x 10³t) volts. The peak voltage Am of the modulating signal is______

40

28. A circular disc reaches from top to bottom of an inclined plane of length ‘L’. When it slips down the plane, it takes time’t₁’.when it rolls down the plane, it takes time t₂. The value of  . The value of x will be_____

2

29. The amplitude of wave disturbance propagating in the positive x-direction is given by at time t = 0 and  at t = 1s, where x and y are in metres. The shape of wave does not change during the propagation. The velocity of the wave will be_____ m/s.

2

30. In the reported figure, heat energy absorbed by a system in going through a cyclic process is_____πJ.

10

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## JEE Main Solved Paper Question Answer With Solutions

### JEE Main 2021 Paper with Solutions

 ⚫ JEE Main 2021 Paper with Solutions – 20th July – Shift 1 1. JEE Main Physics Question Paper 2. JEE Main Chemistry Question Paper 3. JEE Main Maths Question Paper