The current flowing in an electrical or electronic circuit can suddenly increase when a component part fails. This can cause serious damage to other components in the circuit, or create a fire hazard. To protect against this, a fuse or a device called a "circuit breaker" can be wired into a circuit.
The point where those electrons enter an electrical circuit is called the "source" of electrons. The point where the electrons leave an electrical circuit is called the "return" or "earth ground". The exit point is called the "return" because electrons always end up at the source when they complete the path of an electrical circuit.
They have been widely used in primary and secondary education (e.g. Duit 1991; de Bóo and Asoko 2000; Asoko and Boo 2001). Analogies are particularly suitable for use in physics (Reiners and Glynn 1995; Kircher and Hauser 1995). They are ideal for teaching principles relating to electricity (Dupin and Johsua 1989, Cosgrove 1995). Students can use analogies to relate with something they are already familiar with and see the similarities between the two systems.
A load of an electrical circuit may be as simple as those that power home appliances like refrigerators, televisions, or lamps or more complicated, such as the load on the output of a hydroelectric power generating station.
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