Practice problems on NEET, NEET 2021

Question 1

The escape velocity from the Earth's Surface is v. The escape velocity from the surface of another planet having a radius, four times that of Earth and same mass density is:

Accepted Answer

4 v

Answer

v

Answer

2 v

Answer

3 v

Question 2

A cup of coffee cools from 90∘C  to 80∘C  in t minutes, when the room temperature is 20∘C . The time taken by a similar cup of coffee to cool from 80∘C  to 60∘C  at a room temperature same at 20∘C  is :

Accepted Answer

513​t

Answer

135​t

Answer

1013​t

Answer

1310​t

Question 3

Polar molecules are the molecules:

Accepted Answer

Having a permanent electric dipole moment

Answer

Having zero dipole moment

Answer

Acquire a dipole moment only in the presence of electric field due to displacement of charges

Answer

Acquire a dipole moment only when magnetic field is absent

Question 4

Find the value of the angle of emergence from the prism. Refractive index of the glass is 3​ .

Accepted Answer

60∘

Answer

90∘

Answer

30∘

Answer

45∘

Question 5

A parallel plate capacitor has a uniform electric field ′E′  in the space between the plates. If the distance between the plates is 'd' and the area of each plate is 'A', the energy stored in the capacitor is: (ε0​=  permittivity of free space)

Accepted Answer

21​ε0​E2Ad

Answer

ε0​E2Ad​

Answer

21​ε0​E2

Answer

ε0​EAd

Question 6

A particle is released from height S from the surface of the Earth. At a certain height its kinetic energy is three times its potential energy. The height from the surface of earth and the speed of the particle at that instant are respectively:

Accepted Answer

4S​⋅23gS​​

Answer

4S​,23gS​

Answer

4S​,23gS​​

Answer

2S​,23gS​​

Question 7

The velocity of a small ball of mass M and density d, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is 2d​ , then the viscous force acting on the ball will be:

Accepted Answer

2Mg​

Answer

2Mg

Answer

Mg

Answer

23​Mg

Question 8

The electron concentration in an n-type semiconductor is the same as hole concentration in a p-type semiconductor. An external field (electric) is applied across each of them. Compare the currents in them.

Accepted Answer

Current in n-type > current in p-type

Answer

No current will flow in p-type, current will only flow in n-type

Answer

Current in n-type = current in p-type

Answer

Current in p-type > current in n-type

Question 9

An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of 105mathrm m/mathrms  parallel to the conductor. The perpendicular distance between the electron and the conductor is 20mathrm cm  at an instant. Calculate the magnitude of the force experienced by the electron at that instant.Electron v=105mathrm m/mathrms

Accepted Answer

8×10−20 N

Answer

4×10−20 N

Answer

8π×10−20 N

Answer

4π×10−20 N

Question 10

An electromagnetic wave of wavelength ′λ′  is incident on a photosensitive surface of negligible work function. If ' m ' mass is of photoelectron emitted from the surface has de-Broglie wavelength λd​ , then :

Accepted Answer

λ=(h2mc​)λd2​

Answer

λ=(mc2 h​)λd2​

Answer

λ=(hc2m​)λd2​

Answer

λd​=(h2mc​)λ2

Question 11

Two charged spherical conductors of radius R1​  and R2​  are connected by a wire. Then the ratio of surface charge densities of the spheres (σ1​/σ2​) is :

Accepted Answer

R1​R2​​

Answer

R22​R12​​

Answer

R2​R1​​

Answer

(R2​R1​​)​

Question 12

An inductor of inductance L, a capacitor of capacitance C and a resistor of resistance 'R' are connected in series to an ac source of potential difference V volts as shown in figure. Potential difference across L, C and R is 40 V, 10 V and 40 V, respectively. The amplitude of current flowing through LCR series circuit is 102​ A . The impedance of the circuit is :

Accepted Answer

5Ω

Answer

42​Ω

Answer

5/2​Ω

Answer

4Ω

Question 13

For a plane electromagnetic wave propagating in x-direction, which one of the following combination gives the correct possible directions for electric field (E) and magnetic field (B) respectively?

Accepted Answer

−j^​+k^,−j^​−k^

Answer

−j^​+k^,−j^​+k^

Answer

j^​+k^,j^​+k^

Answer

j^​+k^,−j^​−k^

Question 14

Consider the following statements (A) and (B) and identify the correct answer.(A): A zener diode is connected in reverse bias, when used as a voltage regulator.(B): The potential barrier of p-n junction lies between 0.1 V to 0.3 V.

Accepted Answer

(A) is correct and (B) is incorrect

Answer

(A) is incorrect but (B) is correct

Answer

(A) and (B) both are correct

Answer

(A) and (B) both are incorrect

Question 15

The equivalent capacitance of the combination shown in the figure is :

Accepted Answer

2 C

Answer

3C/2

Answer

3 C

Answer

C/2

Question 16

In a potentiometer circuit a cell of EMF 1.5 V gives balance point at 36 cm length of wire. If another cell of EMF 2.5 V replaces the first cell, then at what length of the wire, the balance point occurs?

Accepted Answer

60 cm

Answer

62 cm

Answer

21.6 cm

Answer

64 cm

Question 17

A capacitor of capacitance ' C′ , is connected across an ac source of voltage V, given byV=V0​sinωt The displacement current between the plates of the capacitor, would then be given by:

Accepted Answer

Id​=Vo​ωCcosωt

Answer

Idl​=V0​ωCsinωt

Answer

Id​=ωCV0​​cosωt

Answer

Id​=ωCV0​​sinωt

Question 18

A dipole is placed in an electric field as shown. In which direction will it move?

Accepted Answer

Towards the right as its potential energy will decrease

Answer

Towards the right as its potential energy will increase

Answer

Towards the left as its potential energy will increase

Answer

Towards the left as its potential energy will decrease

Question 19

The number of photons per second on an average emitted by the source of monochromatic light of wavelength 600 nm , when it delivers the power of 3.3×10−3  watt will be : (h=6.6×10−34Js)

Accepted Answer

1016

Answer

1015

Answer

1018

Answer

1017