e4 introducing electricity part 3
TRANSCRIPT
E4C
HA
PTER
Introduction to Electricity
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E4C
HA
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?
E4C
HA
PTER
Introduction to Electricity
Electron flow in a circuitElectron flow in a circuit
E4C
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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
E4C
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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?
E4C
HA
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
E4C
HA
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
E4C
HA
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
E4C
HA
PTER
Introduction to Electricity
• By using a voltmeter• SI unit: volt (V)
- Named after Italian scientist: Alessandro Volta
Measuring voltageMeasuring voltage
E4C
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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?
E4C
HA
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
E4C
HA
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
E4C
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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?
E4C
HA
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
E4C
HA
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
E4C
HA
PTER
Introduction to Electricity
Complete Theory WB Pg. 34 - 37Complete Theory WB Pg. 34 - 37
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