Identify the correct statements among the following:
A. A current carrying wire is electrically charged.
B. The drift velocity of electrons in a metallic wire will decrease if the temperature of the wire is increased.
C. The emf of a cell depends on the internal resistance of the cell.
D. The internal resistance of dry cells is much higher than the common electrolytic cells.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B and D only
(A) A current carrying wire is electrically charged. — Incorrect. In a current-carrying wire, electrons enter and leave any section at the same rate; the wire stays electrically neutral.
(B) The drift velocity of electrons in a metallic wire will decrease if the temperature of the wire is increased. — Correct. A rise in temperature makes the ions vibrate more, so collisions are more frequent and the relaxation time τ decreases. For the same applied potential difference,
\( \displaystyle v_d = \frac{eE}{m}\,\tau \)
also decreases.
(C) The emf of a cell depends on the internal resistance of the cell. — Incorrect. The emf is set by the chemistry of the electrodes and electrolyte. The internal resistance affects only the terminal voltage when current flows, \( V = \varepsilon - Ir \).
(D) The internal resistance of dry cells is much higher than the common electrolytic cells. — Correct. Dry cells have a paste electrolyte and give only small currents, because their internal resistance is much larger.
NCERT (2026-27):
Cells, Emf, Internal Resistance – “… Thus, emf \( \varepsilon \) is the potential difference between the positive and negative electrodes in an open circuit, i.e., when no current is flowing through the cell.”
Cells, Emf, Internal Resistance – “… The actual values of the internal resistances of cells vary from cell to cell. The internal resistance of dry cells, however, is much higher than the common electrolytic cells.”