Question

Consider a simple circuit shown in figure   stands for a variable resistance R′. R′ can vary from R₀ to infinity. r is internal resistance of the battery (r << R << R₀).

1. Potential drop across AB is nearly constant as R ′ is varied.
2. Current through R′ is nearly a constant as R ′ is varied.
3. Current I depends sensitively on R′.
4. `I ≥ V/(r + R)` always.

Options

• a and b

• b and c

• c and d

• a and d

Answer 1

a and d

Explanation:

As r << R << R₀ < R' from question, R' > R and R' and R are in parallel combination, so the equivalent resistance will be always less than R. So `I ≥ V/(r + R)`  and potential across AB will remain nearly constant. 

Important point: In parallel combination of resistances, the equivalent resistance is smaller than smallest resistance present in combination.