WB JEE 2020 | Electrostatics Question 16 | Physics

1

WB JEE 2020

MCQ (Single Correct Answer)

+1

-0.25

Four identical point masses, each of mass m and carrying charge + q are placed at the corners of a square of sides a on a frictionless plane surface. If the particles are released simultaneously, the kinetic energy of the system when they are infinitely far apart is

A

$${{{q^2}} \over a}(2\sqrt 2 + 1)$$

B

$${{{q^2}} \over a}(\sqrt 2 + 2)$$

C

$${{{q^2}} \over a}(\sqrt 2 + 4)$$

D

$${{{q^2}} \over a}(\sqrt 2 + 1)$$

2

WB JEE 2020

MCQ (Single Correct Answer)

+1

-0.25

A very long charged solid cylinder of radius a contains a uniform charge density p. Dielectric constant of the material of the cylinder is K. What will be the magnitude of electric field at a radial distance x (x < a) from the axis of the cylinder?

A

$$p{x \over {{\varepsilon _0}}}$$

B

$$p{x \over {{2k\varepsilon _0}}}$$

C

$$p{{{x^2}} \over {2a{\varepsilon _0}}}$$

D

$$p{{{x^{}}} \over {2k}}$$

3

WB JEE 2020

MCQ (Single Correct Answer)

+2

-0.5

Two pith balls, each carrying charge + q are hung from a hook by two springs. It is found that when each charge is tripled, angle between the strings double. What was the initial angle between the strings?

A

30$$^\circ $$

B

60$$^\circ $$

C

45$$^\circ $$

D

90$$^\circ $$

4

WB JEE 2019

MCQ (Single Correct Answer)

+1

-0.25

Eleven equal point charges, all of them having a charge +Q, are placed at all the hour positions of a circular clock of radius r, except at the 10 h position. What is the electric field strength at the centre of the clock?

A

$${Q \over {4\pi {\varepsilon _0}{r^2}}}$$ from the centre towards the mark 10

B

$${Q \over {4\pi {\varepsilon _0}{r^2}}}$$ from the mark 10 towards the centre

C

$${Q \over {4\pi {\varepsilon _0}{r^2}}}$$ from the centre towards the mark 6

D

Zero.