Ohms Law
German physicist Georg Ohm discovered "Ohms" law in 1827 while doing experiments on how well metals conducted electricity. 
Ohm's Law is the equation V = I * R
Knowing two items in this equation allows you to calculate the third.
Ohm's Law confirms that the voltage (V) equals the electrical current (I) times the resistance (R) in an electrical circuit.
Most components in an electrical circuit obey Ohm's Law. Components that change temperature alot when electricity flows do not obey this law and it wont be accurate. e.g light bulb / heating element.
It is a reality that when amps are increased through a circuit, temperature is also increased so Ohms law is usually used as an approximation.
You can measure any of the parameters with a modern multimeter.
The following equations can be used to find volts, resistance and current as long as the other two measures are identified.:
I = V / R (Current (I) = Voltage Divided by Resistance)
V = I x R (Voltage = Current (I) multiplied by Resistance)
R = V / I (Resistance = Voltage divided by Current (I) )
Resistance and the Ohm
Resistance is measured in Ohms (symbol: Ω) .
Resistance is a measure of how much the current is slowed down.
The bigger the resistance, the smaller the current.
An ohm (symbol: Ω) is a resistance in a conductor that produces a potential difference of one volt when a current of one amp is flowing through it.
To calculate the resistance of a component. firstly, we need to measure the current flowing through it, and the voltage across the component.
If the ammeter reads 3 A, and the voltmeter reads 9 V across the component,.
Resistance = Volts divided by current.
R = V / I
R = 9 / 3
3 Ohms. Resistance
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