WB JEE 2020 | Electrostatics Question 22 | Physics

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

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

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

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

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

WB JEE 2020

MCQ (Single Correct Answer)

-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?

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

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

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

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

WB JEE 2020

MCQ (Single Correct Answer)

-0.5

A pair of parallel metal plates are kept with a separation d. One plate is at a potential + V and the other is at ground potential. A narrow beam of electrons enters the space between the plates with a velocity v₀ and in a direction parallel to the plates. What will be the angle of the beam with the plates after it travels an axial distance L?

$${\tan ^{ - 1}}\left( {{{eVL} \over {md{v_0}}}} \right)$$

$${\tan ^{ - 1}}\left( {{{eVL} \over {mdv_0^2}}} \right)$$

$${\sin ^{ - 1}}\left( {{{eVL} \over {md{v_0}}}} \right)$$

$${\cos ^{ - 1}}\left( {{{eVL} \over {mdv_0^2}}} \right)$$

WB JEE 2020

MCQ (Single Correct Answer)

-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?

30$$^\circ $$

60$$^\circ $$

45$$^\circ $$

90$$^\circ $$

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