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The storage battery of a car has an emf of $$12 V$$. If the internal resistance of the battery is $$0.4 \Omega$$, what is the maximum current that can be drawn from the battery?
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QuestionPhysicsClass 12

The storage battery of a car has an emf of $$12 V$$. If the internal resistance of the battery is $$0.4 \Omega$$, what is the maximum current that can be drawn from the battery?

$$30\ A$$
4.6
4.6

Solution

Given: emf,$$E=12\;V$$
Internal resistance $$r=0.4 \ \Omega$$
Output voltage,
$$V=E-Ir$$
$$r=0.4\; \Omega$$
and for maximum output voltage external resistance, $$R$$ will be $$0$$.
As per Ohm’s Law,
$$V=\mathit{IR}$$
On substituting the given values, we have
$$E=I(R+r)$$
$$I=\frac E{R+r}$$
$$I=\frac{12}{0+0.4}$$
$$I=30A$$
Hence, the maximum current that can be drawn from the battery is$$30\;A$$.