Which of the following statement(s) is/are incorrect?
(A) The Kirchhoff's laws are equally applicable in alternating current circuit and direct current circuits.
(B) It is not necessary that the wire stretched on the metre bridge must have a uniform cross-sectional area.
(C) The internal resistance of the cell does not affect the reading of the null point in metre bridge.
(D) Electrical potential has no direction, the electrical potential gradient has a direction.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B) only
(A) The Kirchhoff's laws are equally applicable in alternating current circuit and direct current circuits. — True statement. Kirchhoff's rules express conservation of charge and of energy, so they hold at every instant in an a.c. circuit as well, when the instantaneous currents and voltages are used.
(B) It is not necessary that the wire stretched on the metre bridge must have a uniform cross-sectional area. — False statement. The bridge relies on the potential drop being proportional to the length of the wire, which holds only for a uniform wire.
\( \displaystyle \frac{R}{S} = \frac{l}{100 - l} \)
(C) The internal resistance of the cell does not affect the reading of the null point in metre bridge. — True statement. At the null point the galvanometer shows no current and the balance condition above involves only the resistances and the lengths, not the cell.
(D) Electrical potential has no direction, the electrical potential gradient has a direction. — True statement. Potential is a scalar; its gradient \( -dV/dr \) is the electric field, which is a vector.
Only (B) is incorrect, which is Option (2).