50
The series circuit offers a single,
continuous, path for current flow from the
negative side of the electromotive force source
to the positive one. The pieces of equipment
or different electrical devices are connected by
wires that give only one path to follow. In the
diagram of a simple circuit Fig. 7, the symbol
on the left indicates the source of electric current, and the symbol on the right
indicates the source of resistance, e.g. a light bulbs. The arrows indicate the
electron flow.
Fig. 8 shows how two or more bulbs can be
connected in a series circuit. Since the current has
only one path to follow, all the lights in the
circuit will go out if even one bulb burns out.
In a parallel circuit, two or more bulbs are
placed parallel to each other so that the current
has more than one path through which it can flow. In that way, as it is shown in
the Fig. 9, the current is divided up among the three resistors. If one burns out,
the current will flow through the other two. Household electricity is connected
by parallel circuits so that the whole circuit does not fail if one piece of
electrical equipment burns out.
Fig.9
Fig.10
Fig.11
The two kinds of circuits can also be used together in a series parallel
circuit. The Figures 10 and 11 show two possible arrangements. In order to set
up a circuit, it is necessary to have sufficient voltage for overcoming the
resistance. Here, Ohm’s law becomes a useful and necessary tool for electrical
engineers.
Electrical circuits have to be protected. If there are too many electrical
devices, the conducting wire may overheat and cause fire or serious injuries. To
prevent this, fuses, through which all the current in the circuits passes, are built
into the circuits.
A fuse is an intentionally weakened element that opens the circuit
automatically if it is overloaded. It has a wire with a low melting point and
when the fuse heats up, the wire melts and the circuit is broken.
Fig.7
Fig.8
