You have installed a new battery of emf 12 V and internal resistance 5.0 x 10^-2 Ω in your car. You self-start your car and it draws a current of 90 A. What would be the teminal voltage of battery when the self-starter is working ?

• Emf of the battery (ε) = 12 V
• Internal resistance of the battery (r) = 5.0 x 10^-2 Ω
• Current drawn (I) = 90 A

As, terminal voltage (V) of the battery is given by,

$\text V = \text ε - \text {Ir} \\[1em] = 12 - 5 \times 10^{-2} \times 90 \\[1em] = 12 - 450 \times 10^{-2} \\[1em] = 12 - 4.5 \\[1em] = 12 - 4.5 \\[1em] = 7.5\ \text V$

Hence, the teminal voltage of battery is 7.5 V.