The condition for electromagnetic induction is that
A. There must be a relative motion between the coil of wire and galvanometer.
B. There must be a relative motion between the coil of wire and a magnet.
C. There must be a relative motion between the galvanometer and a magnet.
D. All of the above.

Hint:We are asked about the condition for electromagnetic induction. To answer this first understand what electromagnetic induction is, how a magnetic field can affect a coil. Use those concepts to analyze the given options one by one and select the appropriate option.

Complete answer:
First, let us know about electromagnetic induction.Electromagnetic induction is a process to generate or induce current in a closed circuit or in a coil by changing the magnetic field or magnetic flux through the coil. Let us analyze the given options one by one.

Option A :- Here it is said about relative motion between the coil of wire and galvanometer. Galvanometer is a device which is used to detect electric current or measure small current. The relative motion between coil of wire and galvanometer will not induce current in the coil. Therefore, option A is incorrect.

Option B :- Here it is said about relative motion between the coil of wire and a magnet. We know from the definition of electromagnetic induction above that current is induced in the coil when there is change in magnetic field. When there is relative motion between the coil of wire and a magnet the magnetic field through the wire will also change and this change in magnetic field will induce a current in the coil. Therefore, option B is correct as for electromagnetic induction there should be change in magnetic flux, that is there should be relative motion between the coil of wire and the magnet.

Option C :- Here it is said about relative motion between the galvanometer and a magnet. A galvanometer is used to detect current. Relative motion between the galvanometer and the magnet will not have any effect on the magnetic flux through the coil and there will be no induced current. Therefore, option C is incorrect.

Hence, the correct answer is option B there must be a relative motion between the coil of wire and a magnet.

Note:Electromagnetic induction was first discovered by experimental physicist Michael Faraday. There are two important laws of electromagnetic induction, known as Faraday’s laws. According to Faraday’s first law when a conductor is placed in a changing magnetic field, an electromotive force is induced in the conductor and in case of closed circuit current is induced. According to Faraday's second law the induced electromotive force or emf in the coil is equal to the change in magnetic flux through the coil.