# Current and voltage

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## What is current?

We use the term current to describe the movement of electrical charges, such as electrons. This way, we can compare a large current to a small current. A large current has more electrons moving through an area at a time than a small current.

## Measuring current

After hearing of Hans Christian Oersted's observations of the effect of electricity on magnets in 1820, French physicist André-Marie Ampère dedicated himself to the study of electromagnetism. In accordance with his work in the field, the standard measurement of current is an ampere, or amp for short.

An ampere is the movement of one coulomb each second. A coulomb is a group of 6.25 x 1018(which is 6 250 000 000 000 000 000) electron charges. That means, if one amp of current flows in a circuit, 6 250 000 000 000 000 000 electrons pass by in one second.

We use milliamps to measure small currents. A milliamp (mA) is one-thousandth of an amp, which is 6.25 x 1015(or 6 250 000 000 000 000) electrons passing by in one second. If placed in a circuit, an instrument called an ammeter will measure the current.

In a circuit, the conventional current is the path from the positive terminal to the negative terminal, named after the initial belief that current flowed from positive to negative. Now, although we know that the electrons that make up electricity flow from the negative terminal to the positive terminal, against the conventional current, we continue to use the traditional labelling today.

## Voltage

In the early 19th century, Italian physicist Alessandro Volta played with the chemistry of various metals, which led him to discover a source of power. His invention, the voltaic pile, eventually led to the creation of the battery.

In Alessandro's honour, scientists now refer to the available energy in a circuit in volts (V), the standard unit of measurement. If you think of amps as the speed of a current, voltage is the amount of current available to be pushed through. This is a measure of electrical pressure, which you may compare with water pressure. If you have a lot of water moving through a small pipe, the water pressure will be higher than the same amount of water in a large pipe. Voltage works the same way, as it only occurs where there is an imbalance of electrons. A higher voltage indicates that there is a greater imbalance of electrons.

To calculate voltage, we apply the following formula:

Voltage = Current x Resistance

We measure voltage with a voltmeter. A voltmeter measures the amount of energy that is available to move between two points. To do this, it 'counts' the number of electrons at one point compared to another and measures the difference between them. A nine-volt (9 V) battery, for example, has six times as many electrons available to power something as a 1.5 V battery. The electricity available in an average Australian household is 220-240 V, which is twice as much as a household in the USA, which has a 110-120 V potential. Refer Image 1

## Wattage

To continue the international flavour of the history of electricity, Scottish inventor James Watt also has a unit of measurement named in his honour. Honouring the engineer, best known for making improvements to the steam engine in the late 18th century, is the watt (W), which is a unit of power.

The pushing force from the voltage, combined with the speed of the current in amps combines to produce the actual amount of power that passes through an electrical device. We measure this power in watts. A compact fluorescent bulb uses about nine watts (9 W) of power compared to an incandescent globe (75 W) that emits the equivalent amount of light. This is why using compact fluorescent bulbs instead of incandescent bulbs saves energy.

We measure the power consumed by larger devices, such as a refrigerator, in kilowatts (kW). One kilowatt is 1000 watts. Even larger electrical devices use power in megawatts (mW), which is one million watts. Refer Image 2

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### Question 1/5

1. How many charges does one coulomb contain?

 1820 220-240 6.25 x 1015 6.25 x 1018