Electromagnetic Bell

This animation shows the design of an electric bell. The electric bell is composed for several parts.

1. A hammer with a permanent magnet attached at the bottom and which hits the gongs when the magnetic field from two current carrying coils pushes it away from the coils.

2. The two red gongs (bells) which are hemispherical in shape and provide a loud ringing noise when hit by the hammer.

3. The two current carrying coils which are wrapped in opposite handedness around some soft iron that increases the magnetic field that they provide at the permanent magnet. Note tthese coils are shown in cross section and the direction of the current in them is shown by either a dot at the center of the wire which denotes flow toward the observer or a cross on the wire that denotes flow away from the observer. These directions switch every half cycle where the cycle can be seen on the current meter.

4. A meter that shows the direction and magnitude of the current going through the coils.

Both the permanent magnet and the coils show arrows that indicate the direction of their magnetic fields. The direction of the field in the permanent magnet does not change.

However, since the coil carries alternating current, the directions of the field in the coils changes every half cycle. When the directions of the arrow in the coil is the same as that of the permament magnet and they are close together, the permanent magnet is attracted by the coil field. When the directions of the arrow in the coil is the opposite that of the permament magnet normally the magnet would be repelled by the coil, but usually the magnet pole is distant from the coil so there is little repulsion.