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Unit 9: Electricity

Electrical circuits — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 12 1 quiz

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

Electrical circuits — HIA INTERNATIONAL notes: Draw and interpret circuit diagrams using the standard symbols for cell, switch, lamp, buzzer and ammeter.Circuits can be shown as a drawing or as a circuit diagram.Circuit diagrams are easier to draw — components have standard symbo…

  • Standard symbols avoid confusion
  • Different looking components can share one symbol
  • The cell symbol
  • Draw no gaps in the lines
  • A circuit must be a complete loop
  • Open the switch

Part 1 of 7Circuit diagrams

Circuit diagrams
Circuits can be shown as a drawing or as a circuit diagram.
Circuit diagrams are easier to draw
  • Circuit diagrams are easier to draw components have standard symbols and wires are straight lines.
Standard symbols avoid confusion
  • Standard symbols avoid confusion the same symbols are used in all countries.
Different looking components can share one symbol
  • Different looking components can share one symbol for example all types of lamp.

Part 2 of 7Common circuit symbols

ComponentFunction
CellProvides energy to make current flow
LampGives out light
Switch (open)Stops the flow of current when opened
Switch (closed)Allows the flow of current when closed
BuzzerMakes a buzzing sound
AmmeterMeasures the current in the circuit

Part 3 of 7Drawing circuit diagrams correctly

1The cell symbol
  • The cell symbol the longer line is positive and the shorter line is negative.
2Draw no gaps in the lines
  • Draw no gaps in the lines especially at corners and where wires meet components.
3
Do not draw wires through components.
4
Use a ruler for straight lines.

Part 4 of 7Complete circuits

Complete circuits
A circuit must be a complete loop
  • A circuit must be a complete loop for a current to flow.
Open the switch
  • Open the switch and the loop is broken, so the current stops.
In a series circuit
  • In a series circuit a break anywhere stops the current everywhere.

Part 5 of 7Comparing circuits and their uses

Comparing circuits and their uses
Cell, switch and buzzer
  • Cell, switch and buzzer could be used in a doorbell.
Cell, switch, lamp and ammeter
  • Cell, switch, lamp and ammeter could light a room and measure the current.
A smaller current
  • A smaller current means the cell is low on stored energy.

Part 6 of 7Series and parallel circuits

Series and parallel circuits
Series circuit
  • Series circuit only one path, so the current is the same everywhere and the supply voltage is shared between components.
Parallel circuit
  • Parallel circuit separate branches, so the current splits and each branch gets the full supply voltage.
Houses use parallel circuits
  • Houses use parallel circuits so each appliance can be switched separately.

Part 7 of 7Connecting meters

Connecting meters
Ammeter
  • Ammeter connected in series, in the same loop as the component.
Voltmeter
  • Voltmeter connected in parallel across the component.
Both ends of an ammeter look the same in a circuit diagram
  • Both ends of an ammeter look the same in a circuit diagram so the red and black terminals are not drawn.

Key terms

TermMeaning
Circuit diagramA drawing that uses standard symbols to show how a circuit is connected.
Circuit symbolA standard picture used for a component in a circuit diagram.
SwitchA component that opens or closes a circuit.
BuzzerA component that makes a buzzing sound when current flows.
AmmeterA component that measures current.
LampA component that gives out light.
Series circuitA circuit with one path for the current.
Parallel circuitA circuit with more than one path for the current.

Avoid these mistakes

1
Drawing gaps in the circuit lines — leave no gaps at corners or components.
2
Drawing a wire through a component — wires stop at the component.
3
Putting the long line of the cell on the negative side — the longer line is positive.
4
Thinking two different circuit diagrams cannot both be correct — different layouts can show the same circuit.

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