Unlike lightening, in low voltages electrons do not
discharge through air, inspected a medium called circuit
is required to link between concentrated and depleted
Depending to medium resistance, electrons move in a
different quantity to the other end.
In previous chapter we learned about attraction between
positive and negative charges, as well on the
possibility of making bridges between them. By letting
only a certain number of electrons through a circuit, we
can limit the current. Such a current can make a load
heats up or glow a filament in a lamp.
Limiting the flow of current is possible because of
resistance property found in materials. It looks like a
tollgate in a free, slows down the traffic.
Along the way of passing, some electrons collide with
each other, causing a reduction or changing their
direction. In overall, it causes a partial lose of
energy in the form heat.
In another analogy, we may think of current as a flow of
water in a pipe and voltage as pressure of water. As the
diameter of pipe reduces, the amount of water reduces as
well because of more resistance.
Current is a flow of charges. By closing the poles of an
electrical source via a medium, we make a circuit.
Such a source could be a battery.
By adding a switch and an electrical bulb, we will have
a controlled circuit to light up the bulb.
A above mentioned circuit was one of the earliest
experiments done by Tomas Edison which gave way to more
supplicated experiments in a later time.
Doing the above experiment, you will need following
Electricity we use at homes and offices come from power
plants that produce in large amount and transfer it via
overhead power line to the points of consumption.
The unit used for current is Ampere (Amp) which is 6.25×1018
electrons passed per second in a circuit. Instead of
memorizing such a large number, we use another unit
called coulomb after the name of discover of current.
The potential difference between the sides is called
The unit of voltage is volt which is the name another
scientist who built the first battery.
As we discussed before, energy is defined as the ability
to do work.
Volt is the amount of electrical charge required to make
one coulomb to do one specific amount of work, namely
In analyzing the circuits, three named units are very
important. Any extra current or voltage may break down a
circuit. On the other too small to them may not activate
the circuit properly. In the same way, too big a
resistance does not let enough electricity flow in the
circuit. Contrary, too small resistance may cause a big
devastating current in the circuit.
Parallel and series circuits
In a single loop, electrons flow in only one predicted
Such a circuit is called “Series circuit”
Whenever there are other paths for current flow, we will
have parallel circuit. In a parallel circuit the voltage
between two ends is equal, but the amount of current
flow in each branch may differ largely. Insuch a means,
we may draw more current from the source, without making
a breakdown in total circuit.
Simplest form of a motor uses of a multi wire inside a
magnet, connected to a battery. Whenever current passes
through the coil, the produced electromagnetic field
force turns the coil, trying to put the coil in the
direction of north-south of magnet poles. By changing
rapidly the direction of current, we may have a turning