Two identical cells each of emf 1 . 5 V are connected in parallel across a parallel combination of two resistors each of resistance 20 Ω . A voltmeter connected in the circuit measures 1 . 2 V . The internal resistance of each cell is :

Step-by-step solution

Equivalent resistance of the parallel 20   Ω branches will be 10   Ω . Equivalent EMF of the two branches which are in parallel will be, = 1 . 5 r + 1 . 5 r 1 r + 1 r = 1 . 5   V and the equivalent internal resistance for same branches will be, r 2 . For loop containing voltmeter and 10   Ω resistor, 1 . 2 - 10 i = 0   ⇒ i = 0 . 12   A . Reading of voltmeter should be, 1 . 2 = 1 . 5 - i r 2   ⇒ i r 2 = 0 . 3   ⇒ r = 0 . 6 i = 0 . 6 0 . 12 = &#