WB JEE 2020 | Electrostatics Question 22 | Physics

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$$^\circ $$

WB JEE 2019

MCQ (Single Correct Answer)

-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?

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

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

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

Zero.

WB JEE 2019

MCQ (Single Correct Answer)

-0.25

A negative charge is placed at the midpoint between two fixed equal positive charges, separated by a distance 2d. If the negative charge is given a small displacement x(x < < d) perpendicular to the line joining the positive charges, how the force (F) developed on it will approximately depend on x?

F $$ \propto $$ x

$$F \propto {1 \over x}$$

F $$ \propto $$ x²

$$F \propto {1 \over {{x^2}}}$$

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