Question

A 30–ohm resistor and a 60–ohm resistor are connected as shown above to a battery of emf 20 volts and internal resistance r. The current in the circuit is 0.8 ampere. What is the value of r?

(A) 0.22 Ω 

(B) 4.5 Ω 

(C) 5 Ω 

(D) 16Ω 

(E) 70 Ω

Answer 1

The correct option is: (C) 5 Ω 

Explanation:

Total resistance = ℰ/I = 25 Ω. Resistance of the 30 Ω and 60 Ω resistors in parallel = 20 Ω adding the internal resistance in series with the external circuit gives R_total = 20 Ω + r = 25 Ω.