Internal resistance of a cell is:
A. decreases with increase in the distance between electrodes.
B. increases with increase in the area of electrodes inside electrolyte
C. decreases with increase in temperature.
D. doesn’t depend on the concentration of the electrolyte.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C only
The internal resistance of a cell is the resistance of its electrolyte between the electrodes. Like any resistance, it grows with the length of the path and falls with the cross-section of the path, \( r\propto d/A \), where d is the separation of the electrodes and A the area of the electrodes dipped in the electrolyte.
A. decreases with increase in the distance between electrodes — Incorrect. A larger separation means a longer path through the electrolyte, so \( r \) increases.
B. increases with increase in the area of electrodes inside electrolyte — Incorrect. A larger area gives a wider path for the current, so \( r \) decreases.
C. decreases with increase in temperature — Correct. Heating an electrolyte makes its ions move more freely (lower viscosity, more ionisation), so its resistance falls.
D. doesn’t depend on the concentration of the electrolyte — Incorrect. The resistance depends on the number of ions available to carry the current, so it changes with the concentration.