Volts, ohms and amps

There has to be some "driving force” that makes electrons flow in a conductor. But what is this force and where does it come from? As a simple example, think of the piece of glass that was rubbed with silk. The glass lost some of its electrons and so became positively charged. The silk gained extra electrons and became negatively charged. The difference between the two charges is called the potential difference. This is the driving force. If a conductor, such as a piece of wire, was made to join up the glass and the silk, electrons would flow back through the wire. The difference in charge would disappear. There would be no potential difference or driving force any more.

The potential difference between two ends of a conductor can be measured. Another name for it is "VOLTAGE”, and the unit by which it is measured is Volts. This name comes from the Italian scientist Alessandro Volta, who, as we saw, found a simpler way of producing a potential difference by rubbing glass with silk.

The larger the voltage, the larger will be the current in a conductor. This relationship between voltage and current was first described by a German scientist named George Ohm in 1827. He found that doubling the voltage doubled the current in a given conductor, and halving the voltage halved the current.. Current is measured in units called amperes, usually shortened to Amps.

This describes how much electricity passes through a given point in a conductor per second.

George Ohm also discovered a relationship between resistance and electric current. He found that the current would be halved, if a wire of twice the resistance was used, or that the current would be doubled if a wire of half the resistance was used. Ohm’s two discoveries resulted in the most famous electric law: Ohm’s Law.

Ohm’s Law states that the current flowing through a conductor is directly proportional to the voltage, and inversely proportional to its resistance. This law is written as an equation

Voltage

________ = Current

Resistance

Resistance is measured in a unit called Ohm, named after George Ohm. Ohm’s Law written in units is:

Volts

_____ = Amperes

Ohms

George Ohm studied how voltage and resistance govern the current in an electric circuit. The unit of resistance - the ohm - is named for him.

Andrè Amperè studied electromagnetism. the amp - the unit of current - is named for him.

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