Which of the following statements is not correct for electromagnetic induction?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The magnitude of induced emf in a circuit is equal to the total change of magnetic flux through the circuit.
Faraday's law gives the magnitude of the induced emf as the rate of change of flux.
\( \displaystyle \varepsilon = N\,\left| \frac{d\Phi}{dt} \right| \)
Option (1) The magnitude of induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit. — A true statement. This is Faraday's law.
Option (2) The magnitude of induced emf in a circuit is equal to the total change of magnetic flux through the circuit. — The statement that is not correct. The emf depends on the rate of change of flux, not on the total change.
Option (3) The induced emf can be increased by increasing the number of turns N of a closed coil. — A true statement. The emf is proportional to \( N \).
Option (4) The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it — A true statement. This is Lenz's law.
NCERT (2026-27):
Faraday’s Law of Induction – “… The magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit.”
Faraday’s Law of Induction – “… The induced emf can be increased by increasing the number of turns N of a closed coil.”
Lenz’s Law and Conservation of Energy – “… The statement of the law is: The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.”