KS3 SCIENCE : ELECTRICITY

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KS3 SCIENCE ELECTRICITY

• By the end of this lesson you should be able to
  make predictions about the current and voltage in
  series circuits, and to use these to predict the
  level of brightness of bulbs in the circuit.

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Quick review Mentally match the symbol with the
correct word, then click again to see the answers.

• Bulb
• Wire
• Battery
• Closed switch
• Ammeter
• Voltmeter

V
A
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Look at the circuit shown.Can you draw the
equivalent circuit diagram?
SERIES CIRCUITS (1)
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What about drawing the circuit diagram for this
one?
SERIES CIRCUITS (2)
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Can you predict which circuit will have the
brighter bulbs?

• Write down a very clear prediction about which
  circuit will have the brighter bulbs.
• Now use a circuit board to set up each circuit,
  and test your prediction.
• Or you can use this website to create simulations
  of the circuits in order to test your
  predictions.
• Once you have tested your predictions you should
  write down whether your initial ideas were
  verified or not. Remember, as a young scientist,
  it is more important to be truthful than correct!

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The result.

• Your investigations should have shown you that
  the bulb in circuit 1 is brighter than either of
  the bulbs in circuit 2.
• The bulbs in circuit 2 should have been equally
  bright, providing they were identical.

Circuit 1
Circuit 2
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The explanation.

• Metals are good electrical conductors since they
  contain free electrons which wander around in
  the wires.
• When the wire is used as part of a closed
  circuit, the electrons are not so aimless
  anymore! They all begin to flow in the same
  direction and a CURRENT is formed.
• Think of a current in the ocean, the faster the
  water flows he stronger the current. In the same
  way, if the electrons flow faster in the wire,
  the electrical current is bigger!
• The cell, and the VOLTAGE it supplies, is what
  pushes the free electrons and makes them go in
  the same direction.

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The electrons return to the cell, get more
energy, and go through the circuit over and over
again
The cell gives electrical energy to the electrons
The electrons use their energy to do work and
produce light in the bulb
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In series circuits

• In a series circuit, there is only one path for
  the current to flow.
• So the electrons have to pass through both of the
  bulbs.
• The only way they can do this is to share the
  energy they have got from the cell, between both
  bulbs.
• Each bulb then gets less energy than one on its
  own, so they cannot produce as much light.
• If the bulbs in a series circuit are identical,
  they will share the total voltage provided
  equally, and the bulbs will be equal in
  brightness!
• If one bulb is bigger, it will use more energy,
  and so a larger portion of the total voltage.