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Class 12 › Physics › Current Electricity
CBSE2026Class Class 12 · Physics2 Marks · Short✅ Verified
A battery of emf 21 V and internal resistance $3\,\Omega$ is connected to a resistor. If the current in the circuit is 3 A, find: (i) the resistance of the resistor, (ii) the terminal voltage of the battery.
✅ Answer & Solution
(i) By Ohm's law for the whole circuit: $$E = I(R + r)$$ $$21 = 3(R + 3)$$ $$7 = R + 3 \Rightarrow R = 4\ \Omega$$ (ii) Terminal voltage: $$V = E - Ir = 21 - (3)(3) = 21 - 9 = 12\ \text{V}$$ Alternatively $V = IR = 3\times4 = 12$ V. Hence $R=4\,\Omega$ and terminal voltage $=12$ V.
