The internal resistance of a 2.1 V cell which gives a current

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is

Given : emf ε = 2.1 V
I = 0.2 A, R = 10Ω
Internal resistance r = ?
From formula.
ε – Ir = V = IR
2.1 – 0.2r = 0.2 × 10
2.1 – 0.2 r = 2 or 0.2 r = 0.1

⇒ r =	0.1	= 0.5 Ω
	0.2