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Electromagnetic Induction

Q: A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil (ii) withdrawn from inside the coil (iii) held stationary inside the coil.

When a coil of insulated copper wire is connected to a galvanometer, following observations will take place for each option:(I) If a bar magnet is pushed into the coil, an electric current will be induced in coil due to electromagnetic induction.(ii) If a bar magnet is withdrawn from inside, again current will be induced in the copper wire due to electromagnetic induction but this time the direction of current will be reverse in galvanometer.(iii) If a bar magnet is held stationary inside the coil then no current is induced and therefore there is no deflection in the galvanometer.

Q: In the arrangement shown in the figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then :

In the figure, two coils are not electrically connected to each other because they are wound on a non conducting rod. Say Coil-1 is connected across a battery through a key. This coil is called primary coil. Coil-2 is connected across a galvanometer. This coil is called secondary coil. When the key is pressed it is observed that, the galvanometer shows a small momentary deflection and then returns to zero. When the key is released, the galvanometer again shows a small momentary deflection, but in opposite direction and then returns to zero. As the coil is connected to a non-conducting rod the self induced electromotive force or voltage is very less and thus the current that flows in one direction slowly diminishes and returns to zero. Similarly when the key is released the current flows in the opposite direction and slowly diminishes.Thus, the rate of change of electromotive force (e.m.f.) in coil-1, decides the magnitude of deflection of galvanometer. The magnetic flux of primary coil is linked through the rod to the secondary coil. Thus, the induced e.m.f. or current is produced in a coil when varying current flows through a neighboring coil.

Q: Describe one experiment to demonstrate the phenomenon of electromagnetic induction.

Definition: Electromagnetic induction is the production of an electromotive force across a conductor when it is exposed to a varying magnetic field. Experiment: Two different coils of copper wire having large number of turns (say 50 and 100 turns respectively) are taken. They are now inserted over a non-conducting cylindrical roll, as shown in figure below. The coil-1, having larger number of turns, is connected in series with a battery and a plug key. Also, the other coil-2 is connected with a galvanometer as shown. The key is initiated and the galvanometer is observed. We will observe that the needle of the galvanometer instantly jumps to one side and then quickly returns to zero, indicating a momentary current in coil-2.The coil-1 is now disconnected from the battery. Now we will observe that the needle momentarily moves, but to the opposite side. It means that now the current flows in the opposite direction in coil-2.Observations:From these observations, we conclude that a potential difference is induced in the coil-2 whenever the electric current through the coil 1 is changing (starting or stopping). As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current inanother conductor, is called electromagnetic induction. In practice, we can induce current in a coil either by moving it in a magnetic field or by changing the magnetic field around it. It is convenient in most situations to move the coil in a magnetic field.

Q: Define electromagnetic induction?

Electromagnetic induction is the production of emf across an electrical conductor in changing magnetic field. This phenomenon was discovered by Michael Faraday.

Q: What is electromagnetic induction?

Hint: Michael Faraday discovered electromagnetic induction in 1831, and James Clerk Maxwell mathematically characterized it as Faraday's law of induction.Solution: Step 1: Definition of electromagnetic induction: Electromagnetic induction is the method of producing induced current in a closed circuit or in a coil by changing the magnetic flux associated with the coil. Electromagnetic induction is the process of creating induction current.

Q: The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.

According to Lenz law, if any conductor is kept in a varying magnetic field then EMF is induced in the conductor and when the loop is close the current will follow through the conductor. The phenomena in which it occure is known as Electromagnetic induction.

Q: Which of the following electrical devices works on the principle of electro-magnetic induction ?

Electric fan works on the principle of electro - magnetic induction. An electric fan works with the help of an electric motor the electric motor consists of a coil of wire wound around a metallic core. As electric current passes through the coil of wires, it produces rotational motion due to electro - magnetic induction.

Q: When a bar magnet is pushed towards ( or away ) from the coil connected to a galvanometer, the pointer in the galvanometer deflects. Identify the phenomenon causing this deflection and write the factors on which the amount and direction of the deflected depends. State the laws describing this phenomenon.

The phenomenon involved is electromagnetic induction (EMI). For the deflection amount depends upon the speed of movement of the magnet or rate of change of flux. Direction depends on the sense ( towards or away) of the movement of the magnet Direction of deflection is according to Lenz's law.The law describing the phenomenon is:The magnitude of the induced emf in a circuit is equal to the rate of change of the magnetic flux through the circuit.\\(\varepsilon =-\dfrac{d\varphi_B}{dt}\\)

Q: What do you understand by the term electromagnetic induction? Explain with the help of a diagram.

The production of electricity from magnetism is known as electromagnetic induction. Let us move a wire \\(AB\\) upward rapidly between the poles of the horseshoe magnet. When the wire is moved up, there is a deflection in the galvanometer pointer which shows a current is produced in the wire \\(AB\\) momentarily. Thus as the wire is moved up through the magnetic field, an electric current is produced in it.