The battery of a car has an internal resistance of $$0.10\Omega$$ and an electromotive force of $$12V$$. When
the battery is connected to the starter motor, the potential difference across the battery terminals
is $$7.0V$$.
What is the current supplied to the starter motor?
Correct option is A. $$50A$$
Let the resistance of motor be $$R$$
So, current in the circuit = $$\dfrac{V}{R+r}$$
$$\implies I =\dfrac{12}{0.1+R}$$ ................(1)
Since the p.d across the motor is $$7.0\ V$$
$$\implies \dfrac{12}{0.1+R}\times R = 7.0\ V$$
$$\implies 12R = 7.0(0.1+R)$$
$$\implies R = \dfrac{0.7}{5}\Omega$$
$$\implies R = 0.14\Omega$$
So,from eq(1)
$$I = \dfrac{12}{0.1+0.14}A$$
$$\implies I = 50A$$