A cell of emf E and internal resistance r is connected to two external resistances R1 and R2 and a perfect ammeter. The current in the circuit is measured in four different situations:
(i) without any external resistance in the circuit.
(ii) with resistance R1 only
(iii) with R1 and R2 in series combination
(iv) with R1 and R2 in parallel combination.
The currents measured in the four cases are 0.42 A, 1.05 A, 1.4 A and 4.2 A, but not necessarily in that order. Identify the currents corresponding to the four cases mentioned above.The current in the circuit to corresponding situations is given by:
i) When there is no external resistance in the circuit,
The current in this case will be maximum because effective resistance is minimum. So, I1 = 4.2 A
ii) In the presence of resistance R1 only, we have
Here, effective resistance is more than (i) and (iv) but less than (iii).
So, I2 = 1.05 A
iii) When R1 and R2 are in series combination, we have
In this case, effective resistance is maximum, so current is minimum.
Thus, I3 = 0.42 A
iv) When R1 and R2 are in parallel combination, we have
Here, effective resistance is more than (i) but less than (ii) and (iii).
So, I4 = 1.4 A
