Page 32 - Basic Electrical Engineering

an electric field between the plates. The positive terminal, or pole of the
voltage source will draw electrons from plate 1 whereas the negative pole
will push extra electrons on to plate 2. Voltage across the capacitor will rise.

The capacitor gets charged equal to the voltage of the source. The
capacitance of a capacitor is a measure of its ability to store charge. The

capacitance of a capacitor is increased by the presence of a dielectric material
between the two plates of the capacitor.

A current-carrying conductor or a coil produces magnetic field around it.
The strength of the magnetic field produced depends on the magnitude of the

current flowing through the conductor or the coil. There is presence of
magnetic field around permanent magnets as well.
A magnet is a body which attracts iron, nickel, and cobalt. Permanent

magnets retain their magnetic properties. Electromagnets are made from coils
through which current is allowed to flow. Their magnetic properties will be

present as long as current flows through the coil.
The space within which forces are exerted by a magnet is called a magnetic

field. It is the area of influence of the magnet.

1.5 ELECTRIC CURRENT, RESISTANCE, POTENTIAL, AND POTENTIAL DIFFERENCE

1.5.1 Electric Current

In any conducting material, the flow of electrons forms what is called current.
Electrons have negative charge. Charge on an electron is very small. For this

reason charge is expressed in terms of Coulomb. Charge of one Coulomb is
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equal to a charge of 6.28 × 10 electrons. The excess or deficit of electrons
in a body is called charge. Thus, electrical current is expressed as a flow of
negative charge, i.e., electrons. Any substance like copper, aluminum, silver,
etc. which has a large number of free electrons (i.e., loosly bound electrons in

the outermost orbit of its atom) will permit the flow of electrons when
electrical pressure in the form of EMF (electromotive force, i.e., voltage) is

applied.