Q4. Assertion: the potential at a point does not depend on the test charge used to find it. Reason: the work done in bringing a test charge to the point is proportional to the charge. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT page 47).
Q5. A proton is released from rest at a point at 200 V and moves to a point at 0 V. How much kinetic energy does it gain, in joules and in eV?
With only the electric force doing work, ΔU = qΔV = 1.6 × 10−19 × (−200) = −3.2 × 10−17 J, so the kinetic energy gain is −ΔU: 3.2 × 10−17 J, or 200 eV (NCERT pages 47 and 59).
Q6. Points A and B are at the same potential. How much quasistatic external work is needed to move a charge from A to B?
None: W = q(VB − VA) = 0, whatever the path (NCERT Eq. (2.4), page 47).