Ohm is a SI (International System) unit of electrical resistance. It is represented by the Greek letter Omega (Ω). Ohm is named after a German physicist Georg Simon Ohm.
Ohm is defined as electrical resistance between two points of an electric conductor, when a potential difference of one volt causes a current of one ampere. The electric conductor should not be under the influence of any electromotive force.
Mathematical expression for ohm can be depicted as:
1Ω = 1V /1A
where the symbol Ω represents electrical resistance in ohm,V represents electric potential in volts and A represents the electric current in ampere.
Generally, resistance of an electric conductor in ohms is constant within certain ranges of voltages, temperature and other factors. It varies greatly in thermistors. A thermistor is kind of resistor, which changes its resistance with respect to temperature.
Ohm is also used to measure electrical impedance in circuits of alternate currents. Electric Impedance is defined as voltage-current ratio in alternating current circuits. The reciprocal of impedance is admittance.
An electrical instrument that is used to measure electrical resistance in ohms is known as Ohmmeter. There are two types of ohmmeters: micro-ohmmeter, measures low value of resistance and mega-ohmmeter, measures large value of resistance.
Various multiples and sub-multiples of ohm in electrical usage are the microohm, milliohm, kilohm, megohm and gigaohm.
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