Electric Field MCQ - Practice Questions & Answers

Solve by difficulty

If a charge q is placed at the centre of the line joining two equal charges Q such that the system is in equilibrium then the value of q is

$Q/2$

$-Q/2$

$Q/4$

$-Q/4$

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ABC is an equilateral triangle. Charges +q are placed at each corner. The electric intensity at O will be

$\frac{1}{4 \pi \varepsilon_0} \frac{q}{r^2}$

$\frac{1}{4 \pi \varepsilon_0} \frac{q}{r}$

Zero

$\frac{1}{4 \pi \varepsilon_0} \frac{3 q}{r^2}$

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Concepts Covered - 1

Electric field

Electric field and electric lines of force:

The space around a charge in which another charged particle experiences a force is said to have an electric field in it.

Electric Field Intensity:

The electric field intensity at any point is defined as the force experienced by a unit positive charge placed at that point.

Electric field intensity,

$E=\frac{F}{q_0}$

where F is the force experienced by q0. The SI unit of E is,

$\frac{Newton}{Columb}=\frac{Volt}{meter}=\frac{Joule}{Coulomb\times Meter}$

The dimensional formula is $[MLT^{-3}A^{-1}]$

The electric field is a vector quantity and due to positive charge is away from the charge and for the negative charge, it is towards the charge.

Electric field due to a point charge:

Consider a point charge placed at the origin O. Let a test charge q0 is placed at P which is at a distance r from O. Force F on test charge q0 is

$F=\frac{1}{4\pi \epsilon_0}\frac{qq_0}{r^2}\hat r$

The electric field at point P due to q is

$E=\lim_{q_0\rightarrow 0}\frac{F}{q_0}=\lim_{q_0\rightarrow 0}\frac{1}{q_0}\frac{1}{4\pi \epsilon_0}\frac{qq_0}{r^2}\hat r=\frac{1}{4\pi \epsilon_0}\frac{q}{r^2}\hat r$

(As q_o tends to zero the electric field produced by q is not affected by q_o.)

The magnitude of the electric field

$E=\frac{1}{4\pi \epsilon_0}\frac{q}{r^2}$

Electric field due to a system of charge:

Electric field obeys the superposition principle. That is the electric field due to a system of charge at a point is equal to the vector sum of all the electric fields.