Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): When the current in a coil is decreasing, the self-induced emf in the coil acts opposite to the direction of the current.
Reason (R): The self-induced emf in a coil opposes any change in the current in the coil.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) is false but (R) is true.
A changing current in a coil changes the flux linked with the coil itself. The emf produced in this way is the self-induced emf, \( \varepsilon=-L\,dI/dt \). Its direction depends on whether the current is growing or falling.
Assertion (A) When the current in a coil is decreasing, the self-induced emf in the coil acts opposite to the direction of the current. — False. For a falling current \( dI/dt \) is negative, so \( \varepsilon=-L\,dI/dt \) is positive. The emf then acts in the same direction as the current and tries to keep it flowing. It acts against the current only while the current is growing.
Reason (R) The self-induced emf in a coil opposes any change in the current in the coil. — True. This is why it is called the back emf. It resists the growth of the current and also its decay. In the same way, inertia resists a change in the motion of a body.
NCERT (2026-27):
Self-inductance – “The self-induced emf is also called the back emf as it opposes any change in the current in a circuit. Physically, the self-inductance plays the role of inertia.”
Self-inductance – “… and shows that L is analogous to m (i.e., L is electrical inertia and opposes growth and decay of current in the circuit).”