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: Understanding the Question:
We must decide which of the four statements are true, then pick the option that lists exactly those.

Step 2: Check statement A:
A current carrying wire has as many positive charges (lattice ions) as free electrons. So it is electrically neutral overall. A is FALSE.

Step 3: Check statement B:
When temperature rises, the ions vibrate more and collisions with electrons become more frequent. The relaxation time falls. Drift velocity \(v_d = eE\tau/m\) then decreases. B is TRUE.

Step 4: Check statement C:
The emf of a cell is the potential difference across its terminals when no current flows. It depends on the chemicals and electrodes, not on the internal resistance. C is FALSE.

Step 5: Check statement D:
Dry cells have a thick paste as electrolyte and small electrode area, so their internal resistance is much higher than that of ordinary liquid electrolytic cells. D is TRUE.

Step 6: Pick the option:
Only B and D are true. That is option 3. Options 1, 2 and 4 include A or C, which are false.

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