Name: An Elementary Study of Domestic Electric Circuits
Uploaded: 2019-07-19
Duration: 5 min 52 s
Description: The electricity we consume is produced through electromagnetic induction at power plants. In this video, we will see the journey of electricity from the powe...

Question

State "Fleming's right-hand rule". With a labelled diagram, explain the working of an AC electric generator.

Accepted Answer

This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction. The induced current is found to be the highest when the direction of motion of the coil is at right angles to the magnetic field. In such a situation, the direction of the induced current is determined by Fleming's right-hand rule. According to this, stretch the thumb, forefinger and middle finger of the right hand so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will show the direction of induced current.

AC generator is a device that converts mechanical energy into electrical energy and it works on the principle of electromagnetic induction. In other words, In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.

An electric generator, as shown in the figure, consists of a rotating rectangular coil $ABCD$ placed between the two poles of a permanent magnet. The two ends of this coil are connected to the two rings $R_{1}$ and $R_{2}$ . The inner side of these rings is made insulated. The two conducting stationary brushes $B_{1}$ and $B_{2}$ are kept pressed separately on the rings $R_{1}$ and $R_{2}$ , respectively. The two rings $R_{1}$ and $R_{2}$ are internally attached to an axle. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit.

When the axle attached to the two rings is rotated such that the arm $AB$ moves up (and the arm $CD$ moves down) in the magnetic field produced by the permanent magnet. Let us say the coil $ABCD$ is rotated clockwise in the arrangement shown in the figure. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along the directions $AB$ and $CD$ . Thus an induced current flows in the direction $ABCD$ . If there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in the external circuit flows from $B_{2}$ to $B_{1}$ .

After half a rotation, arm $CD$ starts moving up and $AB$ moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction $DCBA$ . The current in the external circuit now flows from $B_{1}$ to $B_{2}$ . Thus after every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current. This device is called an AC generator.

State "Fleming's right-hand rule". With a labelled diagram, explain the working of an AC electric generator.

Important Questions on Magnetic Effects of Electric Current

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