A coil \( C_1 \) is connected to a galvanometer G. Second coil \( C_2 \) is connected to a battery through a tapping key. The steady current in the coil \( C_2 \) produces a steady magnetic field. As coil \( C_2 \) is moved towards the coil \( C_1 \), the galvanometer shows a deflection. To obtain a large deflection, one or more of the following steps can be taken:
(A) Use a rod made of soft iron inside the coil \( C_2 \)
(B) Connect the coil \( C_2 \) to a more powerful battery
(C) Move the arrangement of coil \( C_2 \) rapidly towards the coil \( C_1 \)
(D) hold the key pressed continuously
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
By Faraday's law the induced emf, and so the galvanometer deflection, is proportional to the rate of change of the flux linked with \( C_1 \). A larger deflection needs a larger flux or a faster change of it.
(A) Use a rod made of soft iron inside the coil \( C_2 \). — Correct. The iron core greatly increases the magnetic field of \( C_2 \), so the flux through \( C_1 \) changes by more.
(B) Connect the coil \( C_2 \) to a more powerful battery. — Correct. A larger current gives a stronger field and a larger change of flux.
(C) Move the arrangement of coil \( C_2 \) rapidly towards the coil \( C_1 \). — Correct. The same change of flux in a shorter time gives a larger rate of change of flux.
(D) Hold the key pressed continuously. — Incorrect. Keeping the key pressed only keeps the current steady. It does not change the rate at which the flux changes as \( C_2 \) is moved.
NCERT (2026-27):
Faraday’s Law of Induction – “… To obtain a large deflection, one or more of the following steps can be taken: (i) Use a rod made of soft iron inside the coil C2, (ii) Connect the coil to a powerful battery, and (iii) Move the arrangement rapidly towards the test coil C1.”