D. C. Pandey Solutions for Chapter: Electrostatics, Exercise 3: Comprehension Based Questions

Assertion: Two charges $+Q$ each are fixed at two points. If a third charge $+q$ is placed at centre, then this charge is in stable equilibrium condition line joining the charges.

Reason: Electrostatic potential energy of the system in this position is minimum.

Assertion: Two concentric spherical shells $A$ and $B$ are charged by charges $q_A$ and $q_B$. If $q_A$ is negative, then $V_A-V_B$ is also negative.

Reason: $V_A-V_B=\left(\frac{q_A}{4\pi {\epsilon }_0}\right)\left(\frac{1}{R_A}-\frac{1}{R_B}\right)$. Therefore, if $q_A$ is negative, then $V_A-V_B$ is also negative.

Assertion: Two identical balls are charged by $q$. They are suspended from a common point by two insulating threads $I$ each. In equilibrium, the angle between the threads is $180°$. (Ignore gravity)

Reason: In equilibrium tension in the springs is $T=\frac{1}{4\pi {\epsilon }_0}\frac{q·q}{l^2}$

Assertion: With the help of Gauss theorem, we can find electric field at any point.

Reason: Gauss theorem can be applied for any type of charge distribution.

Assertion: When a capacitor is charged by a battery half of the energy supplied by the battery is stored in the capacitor and the rest half is lost.

Reason: If resistance in the circuit is zero, then there will be no loss of energy.

Assertion: A point charge produces a uniform electric field.

Reason: Due to a point charge electric lines of forces are parallel and equidistant.

Assertion: When a metallic plate is partially inserted between the plates of a capacitor its capacity increases.

Reason: If conductivity of conducting plate is more, increase in capacity will be more.

Assertion: No work is done in moving an electric dipole transnationally in uniform electric field.

Reason: Net force on electric dipole in uniform electric field is zero.