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What is electricity?

Voltage: electrical pressure Current: flow of negative charges Resistance: opposition to current flow

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There are three basic properties of an electrical circuit:-

VOLTAGE is electrical pressure

CURRENT is a flow of electrons and occurs only if there is a voltage and a path for the electrons.

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Resistance

RESISTANCE is opposition to current flow. A conductor has a low resistance; an insulator has a high resistance.

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The Atom

ATOMS

Electrons in energy levels

The same number of Electrons as Protons

No electrical charge

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In electrical studies the nucleus remains the same, no protons are added or lost.

The nucleus charge is never changed. An atom will only gain or lose an electron or

electrons. This gain or loss will be in the outer shell.

◦Valency shell If an atom has a charge it becomes an ION

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ATOMS

Like charges repel Unlike charges attract The electrons are pushed from one object

and pulled to the other object. This push/pull or force is called an emf

(voltage). Units Volts, Symbol V (E) By the way, the effective speed of the

electron flow is 7.5 times around the world in 1 second

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Remember

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(+) ION

The ion has lost an electron

The total electrical charge is (+)

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(-) ION

This ion has gained an electron

The total electrical charge is (-)

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If the terminals have an external conducting path, the battery will continue to take electrons from the (+) terminal and place them on the (-) terminal.

The thing to understand is: Electrons are NOT created or destroyed. They simply flow around the conducting

path (circuit).

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WHEN A SOURCE(battery) IS ADDED

ELECTRON FLOW

TIME

When a conducting path is added the additional electrons will move to the free spaces (holes) where electrons are missing

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The electrons flow from (-) to (+). ELECTRON FLOW

The flow of electrons is called CURRENT. CONVENTIONAL CURRENT Flow is (+) to (-). Conventional Current flow is the Australian

Standard. The unit of measurement is the ampere we use

Amps The symbol is A

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Current

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Resistance

A circuit must have an opposition to electron flow. Or the very high current would cause major problems.

This opposition is called RESISTANCE. Measuring Unit - Ohm Symbol - W

The voltage is 240 volts. V = 240V The current is 10 amperes I = 10A The resistance is 200 ohms R = 200W

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Examples