Two coils, A and B, such that A is connected to a battery through a key and B is connected to a galvanometer, are arranged parallel and close to each other. During which of the following duration will the phenomenon of electromagnetic induction be observed?

(a) Two minutes after closing the key.

(b) During the interval the key is taken out.

Correct option is C

Given:

Two coils (A and B):

• Coil A: Connected to a battery through a key.
• Coil B: Connected to a galvanometer.
• Setup: Coils are arranged parallel and close to each other.

Conditions for Electromagnetic Induction: 

Electromagnetic induction occurs when there is a change in magnetic flux through coil B. This can happen during the following durations:

When the key is closed in coil A:

• Closing the key allows current to start flowing through coil A, creating a changing magnetic field.
• This changing magnetic field induces a current in coil B, observed as a deflection in the galvanometer connected to coil B. 

​When the key is opened in coil A:​​

• Opening the key stops the current in coil A, causing a sudden change (decrease) in the magnetic field.
• This changing magnetic field induces a current in coil B, seen as a deflection in the galvanometer.

Note:

• No electromagnetic induction will be observed when the current in coil A is steady (after the key has been closed for some time). This is because a steady current produces a constant magnetic field, leading to no change in magnetic flux through coil B.

​The correct answer is option ( c ) only ( B )