same circuit. Parallel circuits are therefore
not load-sensitive.
A current will always follow the easiest
path that is available. If the wires of a circuit
are uninsulated and touch each other, the
current will pass from one to the other
because this is a shorter and easier path
than the one intended: there will be ashort
circuit.
In the drawing on the left in figure 11.5,
the current will take a shortcut back to the
cell without going through the push button;
the bell will ring continuously whether the
switch is open or closed. In the drawing on
the right, the bell will not ring at all; the cur-
rent will take a shortcut back to the cell with-
out going through the bell.
A short circuit allows a stronger-than-
usual flow of electricity through the wires;
this excessive current causes the wires to
overheat. Afuseorcircuit breakeris a safety
device that opens the circuit before the wire
becomes a fire hazard. Because the fuse is
part of the circuit, it also overheats and a
metal strip in the fuse melts and breaks the
circuit. If the protective device is a circuit
breaker, the excess current of the short cir-
cuit causes the breaker to flip open, inter-
rupting the path of the current.ELECTRICITYFigure 11.3Series circuit.Figure 11.4Parallel circuit.
Figure 11.5Two short circuits. The wire in these circuits is
bare wire. Where the wires are twisted together, the current
would flow from one to the other.