a dry battery of e.m.f. 3 volt supplies current through a circuit in which the resistance can be changed. A high resistance voltmeter is connected across a battery. When the current is 1.5 A, the voltmeter reads 2.7 V. find the internal resistance of the battery.
Here I = 1.5 A
E = 3V
V = 2.7 V
E = V + Ir
=> r = (E-V )/I = (3-2.7)/1.5 = 0.3/1.5
=> r = 0.2 Ω