Dynamo

Consider a coil of fine insulated wire wound on a plastic or cardboard tube. Connect the ends of the coil to a DC milliammeter or galvanometer (for demonstration purposes!). A center-zero meter is preferred for this demonstration. Now take a bar magnet and thrust the magnet into the coil. The meter will deflect. Now withdraw the magnet. The meter deflects the other way. As we insert and withdraw the magnet, the meter deflects from one side to the other. With the magnet stationary, the meter reads zero. What's happening? We see that when the magnet is moving, a current is induced in the coil. The moving magnetic field, from the moving magnet, cuts the conductors forming the coil.

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