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1.1Unit 9: Electricity and circuits

Flow of electricity — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 10 parts Lesson 1 of 5 1 quiz

📚 Cambridge Checkpoint Physics 0893 Hub / Topical Revision
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Lesson summary

1.1 Flow of electricity — CHECKPOINT PHYSICS 0893 notes: Explain that current is the flow of electrons around a complete circuit and which way they move.Cell = a store of chemical energy that can be changed to electrical energy in a circuitBattery = two or more cells joined toget…

  • Pushing electrons
  • Closing a switch
  • Free electrons
  • Without a circuit
  • Positive terminal
  • Negative terminal

Part 1 of 8Cells, 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
Terminals
  • Terminals a cell, battery or power supply has two connections marked + (positive) and − (negative)
Pushing electrons
  • Pushing electrons the negative terminal pushes electrons around the wires of a connected circuit

Part 2 of 8What current is

Current
Current the flow of electrons around a circuit
Electrons
  • Electrons they are tiny particles found in the atoms of all materials
Closing a switch
  • Closing a switch in a simple circuit with a cell, switch and lamp the lamp lights when the switch is closed and electrons flow
Complete circuit
  • Complete circuit electrons flow only when the circuit is complete, and a break stops all the flow

Part 3 of 8Electrons in a metal

Free electrons
  • Free electrons some of the electrons in a metal are free to move through it
Without a circuit
  • Without a circuit the free electrons move randomly
In a circuit
  • In a circuit the electrons all move in the same direction
Size
  • Size electrons are very small, so diagrams of them are not to scale

Part 4 of 8Direction of the electrons

Charge
  • Charge electrons have a negative charge
Rules
  • Rules opposite charges attract and like charges repel
Attract
Attract pull together and repel = push apart
Positive terminal
  • Positive terminal electrons are attracted towards it
Negative terminal
  • Negative terminal electrons are repelled from it
Result
  • Result electrons flow around the circuit from the negative terminal to the positive terminal

Part 5 of 8Charge rules

ChargesEffect
Positive and negativeAttract
Positive and positiveRepel
Negative and negativeRepel

Part 6 of 8Modelling current with a string loop

String loop
  • String loop a loop of string passed through the hands of a group models the wires
Cell
  • Cell the person pulling the string models the cell
Other people
  • Other people they model components such as lamps
Marks on the string
  • Marks on the string they model electrons
Strength
  • Strength the string moves all round the loop at once, as electrons do
Limitation
  • Limitation the model does not show that real electrons are charged particles inside metal

Part 7 of 8Predicting how current flows

1Test set-up
  • Test set-up four lamps in series placed several metres apart
2Prediction
  • Prediction all the lamps light at the same time because the electrons already in the wires start moving everywhere together
3Testable prediction
Testable prediction a hypothesis
4Explanation
  • Explanation free electrons fill the whole circuit, so they all begin to move as soon as the circuit is complete

Part 8 of 8More from the specification

1Drift velocity of conduction electrons
  • Drift velocity of conduction electrons potential differences across conductive metal wires provide an electrostatic means to drive continuous electric current.
2Electric current definition
  • The continuous flow of microscopic negatively charged electrons through a closed conductive loop.
3Complete circuit loop
  • Electricity flows only when there is an unbroken conductive circle connecting the positive and negative terminals of a power source.
4Electron drift in metals
  • In metallic wires, delocalised outer valence electrons are free to move between fixed positive metal ions when a voltage is applied.
5Conventional current vs electron flow
  • Conventional current is defined as flowing from positive to negative, whereas electrons physically flow from negative to positive.

Key terms

TermMeaning
CurrentFlow of electrons in a circuit.
ElectronNegatively charged particle in an atom.
CellStore of chemical energy that provides electrical energy.
BatteryTwo or more cells joined together.
TerminalConnection point of a cell, labelled + or −.
AttractPull together.
RepelPush apart.

Avoid these mistakes

1
Thinking current is used up in the lamp — electrons keep flowing and carry energy to the lamp.
2
Thinking electrons flow from the positive terminal — they flow from the negative terminal to the positive terminal.
3
Thinking a lamp lights in a broken circuit — all flow stops when there is a break.
4
Thinking electrons start only at the cell and take time to reach the lamp — electrons are already in the wires and all start moving together.

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