Which of the following statements are correct?
A. The relative motion between a magnet and a coil is responsible for induction of electric current in the coil.
B. Magnetic flux is a vector quantity.
C. In a closed coil, the magnitude of emf induced is equal to the time rate of change of magnetic flux.
D. Eddy currents oppose the magnetic braking effect in trains.
E. Lenz's law gives the polarity of the induced emf clearly.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, C and E only
Electromagnetic induction is the production of an emf in a coil when the magnetic flux linked with it changes. Faraday's law gives its magnitude and Lenz's law gives its direction.
A. The relative motion between a magnet and a coil is responsible for induction of electric current in the coil. — Correct. In Faraday's experiments a current flows only while the magnet and the coil move relative to each other, which changes the flux.
B. Magnetic flux is a vector quantity. — Incorrect. Flux is the dot product \( \Phi = \vec{B}\cdot\vec{A} \), so it is a scalar quantity; it has a sign but no direction.
C. In a closed coil, the magnitude of emf induced is equal to the time rate of change of magnetic flux. — Correct. This is Faraday's law, \( |\varepsilon| = d\Phi/dt \), for a coil of one turn.
D. Eddy currents oppose the magnetic braking effect in trains. — Incorrect. Eddy currents are the cause of magnetic braking: the currents induced in the moving metal oppose its motion.
E. Lenz's law gives the polarity of the induced emf clearly. — Correct. The induced emf has the polarity that opposes the change of flux producing it (the minus sign in \( \varepsilon = -d\Phi/dt \)).
Note: Statements (A), (B), (C) and (E) of this question are from the latest textbook (2026-27). Statement (D), that eddy currents are used for magnetic braking in trains, is printed only in the pre-rationalised textbook (2022-23). It was removed from the latest book, and it also appears to be out of the CUET 2026 syllabus.
NCERT (2026-27):
The Experiments of Faraday and Henry – “… It shows that it is the relative motion between the magnet and the coil that is responsible for generation (induction) of electric current in the coil.”
Magnetic Flux – “… Magnetic flux is a scalar quantity.”
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.”
Lenz’s Law and Conservation of Energy – “In 1834, German physicist Heinrich Friedrich Lenz (1804-1865) deduced a rule, known as Lenz’s law which gives the polarity of the induced emf in a clear and concise fashion.”
NCERT (Pre-rationalised edition, 2022-23):
Eddy Currents – “… Eddy currents are used to advantage in certain applications like: (i) Magnetic braking in trains: Strong electromagnets are situated above the rails in some electrically powered trains. When the electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train.”