Electrical Circuits
Imagine that you lived 200 years ago. You would have been living in a world without electricity. Consider the
ways in which your life would have been different. There would be no electric lights, television, radio,
refrigerators, or cars.
Many people might argue that harnessing electrical energy has been the most significant technological event
of all time. Our technologies use thousands of devices that rely on electricity and electronics.
The study of electricity can be difficult. One reason why is that we usually can’t see electricity. We know it’s
there because we can see the results of its work. We feel the heat from a blow dryer and watch the paddles
on the ceiling fan turn – but what is electricity?
Electricity is a form of energy that comes from the movement of invisible particles, called electrons, through
an electrical conductor. Electrons are tiny negatively charged particles of an atom.
In electricity, a circuit is a combination of parts connected to form a
complete path through which electrons can flow. A simple circuit consists
of three basic parts: an energy source, a conductor, and a load. These
three parts are essential to all electrical circuits.
Basic Parts of a Circuit
1.
An energy source could be a battery, a solar photovoltaic cell, or
electricity generated from a power plant. We use an electrical plug
to use energy from a power plant.
2.
A conductor provides a low resistance path through which
electricity can flow. Copper and aluminum are the two most
commonly used conductors.
3.
A load is a device that changes electricity into some other useful
form of energy. A load is the device that electricity is being
delivered to. A load could be a light bulb, a buzzer, or an electric
motor. The load converts electrical energy into heat, light,
mechanical, sound, or other useful energy forms.
A circuit without a load is called a short circuit. Without a load
electricity flows in dangerously large quantities through the
conductor and produces heat. A short circuit will usually cause
damage to circuit parts or a fire.
Other Parts of a Circuit
Some electrical circuits have three additional parts to help control the flow of electricity. These
are insulators, a control device, and a protection device.
4.
An insulator is a material that electricity does not easily flow through. Insulators are
used to confine electricity to the desired path. Insulators are very important safety
devices to keep people from being shocked. Examples of insulators are plastic, nylon,
glass, rubber, ceramic, and enamel or varnish. The plastic coating around a wire is an
insulator.
5.
A control device is often a switch used to start and stop the flow of electricity.
6.
A protection device is used to interrupt the circuit in case of a circuit malfunction. An
example of a protection device is a fuse.
A single cell flashlight is an example of a simple circuit. Figure 3-1 (a) shows the construction
details of such a flashlight. Electron flow in the flashlight can be traced by referring to the
electrical diagram in Figure 3-1 (b).
Electrons from a battery always flow from the negative (-) to the positive (+). Electrons leave
the negative end of the cell, travel through the spring, the metal case, the leaf spring of the
switch, the metal reflector, the light bulb, and back to the positive end of the cell. Note that
the spring, case, and reflector are conductors for the flashlight circuit.
A schematic diagram shows the parts of a circuit with electrical symbols. Fig. 3-1 (b) shows the
flashlight circuit in schematic form. Look at the symbols used to represent the switch, lamp,
battery, and conductor. Which way do the electrons flow? Electricity always flows from the
negative to the positive.