Question

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:

• A. A, B and D only
• B. A and D only
• C. B and D only
• D. A, C and D only

Hint:

A wire is neutral. Emf does not depend on internal resistance.

Answer 1

The Correct Option is C

Step 1: Method:
Test each statement against a basic fact or a formula, and keep the ones that pass.

Step 2: Statements A and C fail:
Charge on a wire: a metal conductor has equal numbers of protons in the lattice and electrons, so the net charge is zero even with current. This kills A. For emf, we use \(\varepsilon = V + Ir\). Emf is the terminal voltage at zero current, so it is fixed by the cell chemistry and not by $r$. This kills C.

Step 3: Statement B passes:
With more heat, lattice vibration grows and the mean time between collisions $\tau$ drops. Since $v_d \propto \tau$, drift speed falls.

Step 4: Statement D passes:
A dry cell uses a paste and has a small contact area. This gives a large internal resistance compared with a wet cell such as a lead acid cell.

Step 5: Choose:
Statements B and D pass, which is the third printed option.

Final Answer:
B and D are the only true statements, so option 3. \[ \boxed{\text{Option 3}} \]