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PTER

Introduction to Electricity

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PTER

Introduction to Electricity

• For electricity to flow in a circuit, electrons in the copper atoms of the wires must move from one atom to the next.

• This flow of electron in one direction in a circuit is called an electric current.

What is an electric current?What is an electric current?

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PTER

Introduction to Electricity

Electron flow in a circuitElectron flow in a circuit

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PTER

Introduction to Electricity

• Energy is needed for the electron to move.

• Source of energy: electric cell in the circuit

• Electric cell has:- a positive terminal, and- a negative terminal

• Electrons flow out of the negative terminal of the electric cell, round the circuit and back to the positive terminal of the cell.

Path of electron flowPath of electron flow

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PTER

Introduction to Electricity

• Have you heard of ‘static’ electricity?• It is produced when certain materials, like wool and

plastics, are rubbed against each other. • The rubbing process caused electrons from the surfaces

of one materials to be transferred to the surface of the other material.

• Have you experienced a shock from static electricity before? Recall how the static electricity could have been produced.

Do you know?Do you know?

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PTER

Introduction to Electricity

• By using an ammeter

• SI unit: ampere (A)– Name after French scientist: Andre-Marie Ampere

• Other units: milliamperes (mA)

1 A = 1000 mA

1 mA = 1/1000 A (or 0.001 A)

Measuring the size of an electric currentMeasuring the size of an electric current

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PTER

Introduction to Electricity

• Connected in series in a circuit• Ammeter has:

- A positive (red) terminal - A negative (black) terminal

• Positive terminal is connected to the positive side of the cell

• Negative terminal is connected to the negative side of the cell

Connecting an ammeter to a circuitConnecting an ammeter to a circuit

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PTER

Introduction to Electricity

• Also called the potential difference• An electric cell provides electrical potential energy, thus

pushing the electrons the circuit.• An electron can have a large amount of potential energy

at one point in the circuit and a low amount of potential energy at another point in the circuit.

• The difference in potential energy between the two points is the voltage.

What is voltageWhat is voltage

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PTER

Introduction to Electricity

• By using a voltmeter• SI unit: volt (V)

- Named after Italian scientist: Alessandro Volta

Measuring voltageMeasuring voltage

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PTER

Introduction to Electricity

• In a circuit, electrical components (eg. light bulbs) change some of the electrical energy into other forms of energy.

• The electrons have less potential energy after passing through the component.

• Hence, there is a difference in potential energy or a potential difference.

Why is there a potential difference?Why is there a potential difference?

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PTER

Introduction to Electricity

• Connected in parallel in a circuit• Voltmeter has:

- A positive (red) terminal - A negative (black) terminal

• Positive terminal is connected to the positive side of the cell

• Negative terminal is connected to the negative side of the cell

Connecting a voltmeter to a circuitConnecting a voltmeter to a circuit

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PTER

Introduction to Electricity

• Different electric sources have different voltages.• Example:

- A 9 V electric cell supplies 6 times the energy of a 1.5 V electric cell

- Mains voltage is much greater.- In Singapore, mains voltage is 230 V.

Voltages of electrical sourcesVoltages of electrical sources

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PTER

Introduction to Electricity

• Different countries use different values of mains voltage to provide electricity to electrical appliances.

• The voltage used range from 100 – 240 V• For example: (Values taken from Wikipedia)

• Find out whether you can still charge your handphone if you travel to countries which use a different mains voltage from Singapore.

Country/City Voltage (V)

Japan 100

Canada 120

Indonesia 127 and 230

Philippines, Hong Kong, South Korea 220

Australia, New Zealand 230

Do you know?Do you know?

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PTER

Introduction to Electricity

• Electric cells are connected in series with the positive terminal of one cell touching the negative terminal of the next cell

• Total voltage across all the electric cells = sum of the voltages of the individual cells

Connecting electrical cells to electrical Connecting electrical cells to electrical appliancesappliances

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PTER

Introduction to Electricity

• Electric cells are connected in series with the positive terminal of one cell touching the negative terminal of the next cell

• Total voltage across all the electric cells = sum of the voltages of the individual cells

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PTER

Introduction to Electricity

Complete Theory WB Pg. 34 - 37Complete Theory WB Pg. 34 - 37

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