JEE Main 2021 Question paper (Official) with solutions for February session has been released. It is released separately for four session in February, March, April and May sessions. JEE Main is conducted for providing admission into UG engineering (B.Tech) / architecture courses (B.Arch). These courses are offered by various IITs, NITs and IIITs and other government and non-government engineering institutions. JEE Main question paper and answer key is released by the National Testing Agency (NTA). And solutions are prepared by Kunduz tutors for you. Through this blog, candidates can get the JEE Main 2021 question paper with solutions and also previous year answer key and question papers with all solutions.

## Important Material for JEE Aspirants

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## JEE Main 2021 Question Paper with Solutions- 25 February Shift 2

### Physics JEE Main 2021 Question Paper with Solutions 25 Feb Shift 1

**Question 1**

The truth table for the following logic circuit is

1. | A | B | Y |

0 | 0 | 0 | |

0 | 1 | 1 | |

1 | 0 | 1 | |

1 | 1 | 0 | |

2. | A | B | Y |

0 | 0 | 1 | |

0 | 1 | 0 | |

1 | 0 | 1 | |

1 | 1 | 0 | |

3. | A | B | Y |

0 | 0 | 1 | |

0 | 1 | 0 | |

1 | 0 | 0 | |

1 | 1 | 1 | |

4. | A | B | Y |

0 | 0 | 0 | |

0 | 1 | 1 | |

1 | 0 | 0 | |

1 | 1 | 1 |

Correct Answer: 3

**Question **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)

Correct Answer: 2

**Question **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

- 35 m
- 45 m
- 25 m
- 50 m

Correct Answer: 2

**Question **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

- 9.87 N
- 50 N
- 100 N
- 0.49 N

Correct Answer: 1

**Question **5

An LCR circuit contains resistance of 110 Ω 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

- 1.5 A
- 1 A
- 2 A
- 2.5 A

Correct Answer: 3

**Question **6

Consider the diffraction pattern obtained from the sunlight incident on a pinhole of diameter 0.1 μm. 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

Correct Answer: 4

**Question **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

- √2
- 2
- 1/2
- 1/√2

Correct Answer: 1

**Question **8

An electron of mass me and a proton of mass m_{p}=1836m_{e} are moving with the same speed. The ratio of their de Broglie wavelength λ_{electron} / λ_{proton} will be

- 1/1836
- 918
- 1
- 1836

Correct Answer: 4

**Question **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

- 490.7 nm
- 121.8 nm
- 913.3 nm
- 194.8 nm

Correct Answer: 2

**Question 1**0

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.

Correct Answer: 1

**Question 1**1

Y = Asin(ωt + Φ_{0}) is the time-displacement equation of a SHM. At t = 0 the displacement of the particle is Y=A/2 and it is moving along negative x-direction. Then the initial phase angle Φ_{0} will be:

- π/6
- 2π/3
- 5π/6
- π/3

Correct Answer: 3

**Question 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 :

- 329 nm
- 400 nm
- 382 nm
- 309 nm

Correct Answer: 3

**Question 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:

- c/f
_{c} - c/f
_{m} - c/(f
_{m}+f_{c}) - c/(f
_{c}-f_{m})

Correct Answer: 1

**Question 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.

In the light of the above statements, choose the correct answer from the options given below:

- Both Statement I and Statement II are false.
- Statement I is false but Statement II is true.
- Statement I is true but Statement II is false.
- Both Statement I and Statement II are true.

Correct Answer: 3

**Question 1**5

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:

- q/4ε
_{0} - q/24ε
_{0} - q/48ε
_{0} - q/8ε
_{0}

Correct Answer: 2

**Question 16**

An electron with kinetic energy K_{1} enters between parallel plates of a capacitor at an angle ‘α’ with the plates. It leaves the plates at angle ‘β’ with kinetic energy K_{2}. Then the ratio of kinetic energies K_{1} : K_{2} will be :

- cosβ/sinα
- cosβ/cosα
- cos
^{2}β/cos^{2}α - sin
^{2}β/cos^{2}α

Correct Answer: 3

**Question 1**7

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.

Correct Answer: 3

**Question 1**8

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 :

- π√(m/k)
- π√(m/2k)
- 2π√(m/2k)
- 2π√(m/k)

Correct Answer: 1

**Question 1**9

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 θ and climbs upward. Assuming that it rolls without slipping, how far up the sphere will travel?

- v
_{0}^{2}/5gsinθ - v
_{0}^{2}/2gsinθ - 10v
_{0}^{2}/7gsinθ - 2v
_{0}^{2}/5gsinθ

Correct Answer: 3

**Question **20

If e is the electronic charge, c is the speed of light in free space and h is Planck’s constant, the quantity e^{2}/(4πε_{0}hc) has dimensions of :

- [M L T
^{–1}] - [M L T
^{0}] - [L C
^{–1}] - [M
^{0}L^{0}T^{0}]

Correct Answer: 4

**Question **21

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 xh/3 kg. The value of x is ** _**. (h = Planck’s constant)

Correct Answer: 10

**Question **22

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.

Correct Answer: 36

**Question **23

The percentage increase in the speed of transverse waves produced in a stretched string if the tension is increased by 4% will be ** __**%.

Correct Answer: 2

**Question **24

The peak electric field produced by the radiation coming from the 8 W bulb at a distance of 10 m is

The efficiency of the bulb is 10% and it is a point source. The value of x is ** __**.

Correct Answer: 2

**Question **25

Correct Answer: 180

**Question **26

The initial velocity v_{i} required to project a body vertically upward from the surface of the earth to reach a height of 10R, where R is the radius of the earth, may be described in terms of escape velocity v_{e} such that v_{i}=v_{e}√(x/y). The value of x will be

Correct Answer: 10

**Question **27

Two small spheres each of mass 10 mg are suspended from a point by threads 0.5 m long. They are equally charged and repel each other to a distance of 0.20 m. The charge on each of the sphere is a/21 ⨯10^{–8 }C. The value of ‘a’ will be. [Given g = 10 ms–2]

Correct Answer: 18.50

**Question **28

A reversible heat engine converts one-fourth of the heat input into work. When the temperature of the sink is reduced by 52 K, its efficiency is doubled. The temperature in Kelvin of the source will be ** __**.

Correct Answer: 208

**Question **29

A current of 6 A enters one corner P of an equilateral triangle PQR having 3 wires of resistance 2Ω each and leaves by the corner R. The currents i1 in ampere is **__**.

Correct Answer: 2

**Question **30

Two particles having masses 4 g and 16 g respectively are moving with equal kinetic energies. The ratio of the magnitudes of their momentum is n : 2. The value of n will

Correct Answer: 1

## JEE Main Frequently Asked Questions (FAQs)

**Question 1: **When is JEE Main 2021 exams?

**Answer: **National Testing Agency has announced dates for all phases of JEE Main. First phase is in February 2021 (23, 24, 25 and 26). Second phase is in March 2021 (15, 16, 17 & 18) , third in April 2021 (27, 28, 29 & 30) and fourth in May 2021 (24, 25, 26, 27 & 28). To get more details about JEE Main click here.

**Question 2:** Can I challenge JEE Main 2021 answer key? How?

**Answer:** Yes, candidates who have objection to the answer key given by National Testing Agency can go to jeemain.nta.nic.in , from where they can challenge answer key.

**Question 3:** Does National Testing Agency refund JEE Mains 2021 answer key fees.

**Answer: **Yes, National Testing Agency refund fees if objection is found valid with proper supporting documents.

**Question 4: **Who will conduct JEE Main 2021 Counseling?

**Answer: **Joint Seat Allocation Authority (JoSAA) is responsible for counseling of JEE Main 2021 qualified students.

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