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Unit 9: Electricity

The flow of electricity — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 10 parts Lesson 2 of 12 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

The flow of electricity — HIA INTERNATIONAL notes: Explain current as a flow of electrons and describe the direction in which they move in a complete circuit.Cell = a store of chemical energy that can be changed to electrical energy in a circuit.Battery = two or more cells joined…

  • Every cell, battery and power supply has two terminals
  • In the circuit symbol for a cell
  • Atoms contain smaller particles
  • When electrons move more quickly
  • A complete circuit is needed
  • Some electrons in a metal are free to move

Section 1 of 10Cells, batteries and terminals

Cells, batteries and terminals
Cell
Cell a store of chemical energy that can be changed to electrical energy in a circuit.
Battery
Battery two or more cells joined together.
Every cell, battery and power supply has two terminals
  • Every cell, battery and power supply has two terminals labelled + (positive) and − (negative).
In the circuit symbol for a cell
  • In the circuit symbol for a cell the longer line is positive and the shorter line is negative.
The negative terminal pushes electrons round the wires.

Section 2 of 10Current

Current
Current
Current the flow of electrons around a circuit.
Atoms contain smaller particles
  • Atoms contain smaller particles an electron is one type of these particles.
When electrons move more quickly
  • When electrons move more quickly the current increases; when they move more slowly, it decreases.
A complete circuit is needed
  • A complete circuit is needed if there is a break, all the electrons stop flowing.

Section 3 of 10Electrons in a metal

Electrons in a metal
Some electrons in a metal are free to move
  • Some electrons in a metal are free to move they move randomly when the metal is not in a circuit.
In a circuit the electrons move in the same direction
  • In a circuit the electrons move in the same direction they are carried round by the cell.
Electrons have a negative charge
  • Electrons have a negative charge they are attracted to the positive terminal and repelled from the negative terminal.

Section 4 of 10Attraction and repulsion

Attraction and repulsion
Opposite charges attract
  • Opposite charges attract positive and negative pull together.
Like charges repel
  • Like charges repel positive and positive, or negative and negative, push apart.
Attract means to pull together
  • Attract means to pull together and repel means to push apart.

Section 5 of 10Direction of current

Direction of current
Electrons flow from the negative terminal to the positive terminal.
Conventional current is drawn from + to −
  • Conventional current is drawn from + to − which is the opposite direction to the electron flow.
Current is not used up
  • Current is not used up it is the same all round a series circuit.
Energy, not current, is transferred to the components
  • Energy, not current, is transferred to the components electrons carry electrical energy round the circuit.

Section 6 of 10Voltage and potential difference

Voltage and potential difference
Voltage
Voltage a measure of the energy given to, or transferred by, the charge.
It is measured in volts (V)
  • It is measured in volts (V) with a voltmeter connected in parallel across a component.
More cells in series (the same way round)
  • More cells in series (the same way round) increase the voltage and so the current.

Section 7 of 10Models of current

Models of current
A loop of string passed through the hands of a group is a model of electron flow.
The cell is the person pulling the string
  • The cell is the person pulling the string the other people are components.
The string moves at the same speed all the way round, like electrons in a series circuit.
  • The model cannot show electric charge or attraction and repulsion between electrons.

Section 8 of 10Predicting how lamps light in a long circuit

1All the lamps come on at the same time
  • All the lamps come on at the same time even when they are metres apart, because the free electrons in all parts of the wire start to move together.
2This is a testable prediction
  • This is a testable prediction a prediction that an investigation can check.

Section 9 of 10Key terms

TermMeaning
CellA store of chemical energy that provides energy to make current flow.
BatteryTwo or more cells joined together.
TerminalA connection point on a cell or battery, labelled + or −.
ElectronA tiny negatively charged particle in atoms.
CurrentThe flow of electrons around a circuit.
Complete circuitAn unbroken loop that current can flow around.
AttractPull together.
RepelPush apart.

Section 10 of 10Exam technique

1
Saying the cell makes the electrons — electrons are already in the metal wires.
2
Saying electrons flow from positive to negative — electrons are repelled from the negative terminal and attracted to the positive terminal.
3
Saying the lamp nearest the positive terminal lights first — all lamps light at the same time.
4
Thinking current is used up in the lamp — electrons are not used up; they transfer energy.

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