If a bar magnet is placed axially at a certain distance from a coil that is connected in a closed circuit, then the current in the coil will get induced when:

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If a bar magnet is placed axially at a certain distance from a coil that is connected in a closed circuit, then the current in the coil will get induced when:

The magnet is moved towards or away the coil with constant speed
The magnet is moved towards or away the coil with varying speed
Both 1 and 2 are correct
None of these

Answer 1

CONCEPT:

The experiment of Faraday and Henry:

The experiments carried out by Faraday and Henry explain the phenomenon of electromagnetic induction and its properties.

Experiment 1	Experiment 2	Experiment 3
In this experiment, Faraday connected a coil to a galvanometer G, as shown in the figure. When the North-pole of a bar magnet is pushed towards the coil, the pointer in the galvanometer deflects indicating the presence of electric current in the coil. The deflection lasts as long as the bar magnet is in motion. The galvanometer does not show any deflection when the magnet is held stationary. When the magnet is pulled away from the coil, the galvanometer shows deflection in the opposite direction, which indicates the reversal of the current’s direction. Moreover, when the South-pole of the bar magnet is moved towards or away from the coil, the deflections in the galvanometer are opposite to that observed with the North-pole for similar movements. Further, the deflection (and hence current) is found to be larger when the magnet is pushed towards or pulled away from the coil faster. Instead, when the bar magnet is held fixed and the coil C1 is moved towards or away from the magnet, the same effects are observed. It shows that it is the relative motion between the magnet and the coil that is responsible for the generation (induction) of electric current in the coil.	In the second experiment, Faraday replaced the bar magnet with a second current-carrying coil that was connected to a battery. Here, the current in the coil due to the connected battery produced a steady magnetic field, which made the system analogous to the previous one. As we move the second coil towards the primary coil, the pointer in the galvanometer undergoes deflection, which indicates the presence of the electric current in the first coil. Similar to the above case, here too, the direction of the deflection of the pointer depends upon the direction of motion of the secondary coil towards or away from the primary coil. Also, the magnitude of deflection depends upon the speed with which the coil is moved. Again, it is the relative motion between the coils that induce the electric current.	By this experiment, Faraday showed that the relative motion is not an absolute requirement to induce a current in the primary coil. In this experiment two coils, C1 and C2 held stationary. Coil C1 is connected to galvanometer G while the second coil C2 is connected to a battery through a tapping key K. It is observed that the galvanometer shows a momentary deflection when the tapping key K is pressed. The pointer in the galvanometer returns to zero immediately. If the key is held pressed continuously, there is no deflection in the galvanometer. When the key is released, a momentary deflection is observed again, but in the opposite direction. It is also observed that the deflection increases dramatically when an iron rod is inserted into the coils along their axis.

EXPLANATION:

According to the first experiment of Faraday and Henry, we can say that when a bar magnet is moved towards or away from a coil then an emf gets induced in the coil.
- If the circuit is closed in which the coil is connected then a current will also get induced in the coil.
- The relative motion between the magnet and the coil is required to induce a current in the coil.
When a bar magnet is moved towards or away from the coil with constant speed, there will be a relative motion between the coil and the magnet so current will induce in the coil.
When a bar magnet is moved towards or away from the coil with varying speed, there will be a relative motion between the coil and the magnet so current will induce in the coil. Hence, option 3 is correct.

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If a bar magnet is placed axially at a certain distance from a coil that is connected in a closed circuit, then the current in the coil will get induced when:

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