NEET Practice Questions (MCQs) with Answers & Solutions

The text states: "The unit of C is J mol$^{-1}$ K$^{-1}$." This is consistent with the definition of molar specific heat capacity being per mole, as opposed to specific heat capacity being per unit mass.

According to the NCERT text, 'the potential energy of a system of two charges $q_1$ and $q_2$ is $U = \frac{1}{4\pi\epsilon_0} \frac{q_1q_2}{r_{12}}$' (Eq. 2.22), which shows direct proportionality to $q_1q_2$ and inverse proportionality to $r_{12}$. Also, 'the potential energy U would be the same... because of path-independence of work for electrostatic force.' Therefore, both (b) and (c) are correct.

The NCERT text states, 'If $q_1q_2 > 0$, potential energy is positive. This is as expected, since for like charges ($q_1q_2 > 0$), electrostatic force is repulsive and a positive amount of work is needed to be done against this force to bring the charges from infinity to a finite distance apart.' Both positive-positive and negative-negative charges result in a positive product, hence positive potential energy.

The NCERT states, 'For unlike charges ($q_1q_2 < 0$), the electrostatic force is attractive. In that case, a positive amount of work is needed against this force to take the charges from the given location to infinity. In other words, a negative amount of work is needed for the reverse path (from infinity to the present locations), so the potential energy is negative.' This indicates an attractive force.

The NCERT text explains, 'To bring $q_1$ first from infinity to $r_1$, no work is required.' This is because there are no other charges present at that moment to exert a force against which work needs to be done.

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)