Contrast induced e.m.f. and currents. A galvanometer is connected to a secondary coil. A primary coil is connected to a battery and a switch. What happens to the galvanometer needle when the switch is

Here are the answers to your questions:

b) Contrast between induced e.m.f. and currents

Induced electromotive force (e.m.f.) is the potential difference generated across a conductor due to a change in magnetic flux. It is the cause of an induced current. Induced current is the flow of charge that results from the induced e.m.f. in a closed circuit. Induced e.m.f. can exist even in an open circuit, but induced current requires a complete circuit.

c) Two coils are placed near each other as shown in figure 4. below.

i) What happened to the needle of the galvanometer is on closing the switch?

When the switch is closed, the current in the primary coil rapidly increases from zero to a steady value. This change in current creates a changing magnetic field, which induces a changing magnetic flux through the secondary coil. According to Faraday's Law of Induction, this changing magnetic flux induces an e.m.f. and thus an induced current in the secondary coil. The galvanometer will show a momentary deflection as the current is induced.

ii) If the switch is kept closed

If the switch is kept closed, the current in the primary coil becomes constant. A constant current produces a constant magnetic field, meaning the magnetic flux through the secondary coil is also constant. Since there is no change in magnetic flux, no e.m.f. or current will be induced in the secondary coil. Therefore, the galvanometer needle will return to zero.