Electric Bell

Description

Investigate the working principle of circuit breaker type fuse with this demonstration model. The apparatus is built on a robust plastic base and includes resistive loads to simulate external wiring circuits. Applications of the thermal response of bimetal strips and also electromagnetism (movement from a solenoid) are clearly demonstrated in this model. When a 12 V DC supply is connected (not supplied) the LED lights to show that current is flowing in the external circuit and the bi-metal strip can be seen to bend as its heater coil raises the temperature. After a few minutes the bending is sufficient to trip the mechanism and the current path is broken. At any current selection a short circuit situation can be initiated by pressing the red button and this produces an immediate response from the solenoid to disconnect the supply.

Description

The motor consists of a two pole armature mounted between the ends of two bar magnets. The armature has a two section commutator and a pair of slip-rings on its shaft and is so constructed that the wire cannot slip off the iron core. The upper bearing and brushes for the commutator are mounted on a strong upright. Separate brushes are provided for the commutator and for slip rings and each are connected to a terminal. The magnets are held in position by thumb screws.