Electrostatics MCQs for NEET — Physics Questions with Answers

Equation (2.26) in the NCERT text states, '$U = \frac{1}{4\pi\epsilon_0} \left( \frac{q_1q_2}{r_{12}} + \frac{q_1q_3}{r_{13}} + \frac{q_2q_3}{r_{23}} \right)$'. This formula accounts for the interaction energy between all pairs of charges in the system.

As per the NCERT text, 'Thus, work done in bringing a charge q from infinity to the point P in the external field is qV. This work is stored in the form of potential energy of q.' (Section 2.8.1)

The NCERT text defines, '1 eV = 1.6 \times 10^{-19}$ J.' This is the energy gained by an electron accelerated through a potential difference of 1 volt.

When bringing $q_2$ to its position, 'Work is done not only against the external field E but also against the field due to $q_1$.' (Section 2.8.2)

The NCERT states, 'The external field E is not produced by the given charge(s) whose potential energy we wish to calculate. E is produced by sources external to the given charge(s).' (Section 2.8)

The two charges are $7 \text{ mC}$ (positive) and $-2 \text{ mC}$ (negative). Since they are unlike charges, their product $q_1q_2 < 0$. According to the NCERT material, 'For unlike charges ($q_1q_2 < 0$), the electrostatic force is attractive... so the potential energy is negative.'

The NCERT states, 'Forces of this kind are called conservative forces. Spring force and gravitational force are examples of conservative forces.' It also mentions that 'Coulomb force between two (stationary) charges is also a conservative force.'

As stated in the 'INTRODUCTION' section, 'When an external force does work in taking a body from a point to another against a force like spring force or gravitational force, that work gets stored as potential energy of the body.'

The NCERT text defines, 'Potential energy of the system = the total work done in assembling the configuration.' (Equation 2.29 and point 6 in summary)

According to Eq. (2.28), 'Work done in bringing $q_2$ to $r_2$ is $q_2V(r_2) + \frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r_{12}}$'. This accounts for work against both the external field and the field of $q_1$.