ELECTRICAL CURRENT
The movements of electrons along the conductor in a particular direction produce an electric current. The more electrons which move the greater the current.
AMPERE :
The amount of electron flow is the current and the current is measured in amperes. One ampere of current is said to flow when 6.28 x 10^18 electrons pass a given point in the conductor during a period of one second. The electric current or amperes (abbreviated amps) is measured by an ammeter.
DIRECT AND ALTERNATING CURRENT:
If the electrons flow continuously in one direction along the conductor, the current is said to be direct current (abbreviated d.c.). This is the type of current produced by a battery or a d.c. generator. If the electrons flow in one direction and then flow back again and continue this back and forth motion, the current is said to be alternating current (abbreviated a.c.). This is the type of current produced by an alternator or a.c. generator and is the type of electricity found in home electrical circuits.
VOLT:
Some device is required to apply the necessary pressure to make the electrons flow through the conductor. This potential difference is normally maintained by a battery or generator and is called the electromotive force (e.m.f.) or voltage. One volt is defined as that force which causes an electron flow of one ampere through a resistance of one ohm. The voltage or electrical potential of a circuit is measured by a voltmeter.
OHM :
The opposition to the flow of electrons is called resistance and resistance is measured in ohms. One ohm is the resistance of a wire in which an electrical pressure of one volt causes an electric current of one ampere to flow.
Resistors are used extensively in electrical devices and control the amount of current in various parts of the circuit.
mho :
It is the unit of conductivity. It is reciprocal of ohm. Its symbol is simen or omega reversed.
Ohm's law :
states that an electric current varies directly to the applied voltage and inversely to the resistance. This may be written as
Current in amps = pd in volts/resistance in ohm
Types of Resistances:
The resistances are grouped into following categories on the ohmic value :
• Low resistance : 1 ohm and below
• Medium resistance : Above 1 ohm and upto 1,00,0000 ohm.
• High resistance : Above 1,00,000 ohm.