AQA GCSE Physics 33 Electromagnetism

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AQA GCSE Physics 3-3Electromagnetism

• GCSE Physics pages 254 to 265

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AQA GCSE Specification

• THE MOTOR EFFECT
• 13.7 How can electricity be used to make things
  move?
• Using skills, knowledge and understanding of how
  science works
• to explain how the motor effect is used in
  simple devices.
• Skills, knowledge and understanding of how
  science works set in the context of
• When a conductor carrying an electric current
  is placed in a magnetic field, it may experience
  a force.
• The size of the force can be increased by
• increasing the strength of the magnetic field
• increasing the size of the current.
• The conductor will not experience a force if
  it is parallel to the magnetic field.
• The direction of the force is reversed if
  either the direction of the current or the
  direction of the magnetic field is reversed.
• ELECTRICAL GENERATORS
• 13.8 How do generators work?
• Using skills, knowledge and understanding of how
  science works
• to explain from a diagram how an a.c.
  generator works, including the purpose of the
  slip rings and brushes.

• TRANSFORMERS
• 13.9 How do transformers work?
• Using skills, knowledge and understanding of how
  science works
• to determine which type of transformer should
  be used for a particular application.
• Skills, knowledge and understanding of how
  science works set in the context of
• The basic structure of the transformer.
• An alternating current in the primary coil
  produces a changing magnetic field in the iron
  core and hence in the secondary coil. This
  induces an alternating potential difference
  across the ends of the
• secondary coil.
• The potential difference (p.d.) across the
  primary and secondary coils of a transformer are
  related by the equation
• p.d. across primary / p.d. across secondary
  number of turns on primary / number of turns on
  secondary
• In a step-up transformer the potential
  difference across the secondary coil is greater
  than the potential difference across the primary
  coil.
• In a step-down transformer the potential
  difference across the secondary coil is less than
  the potential difference across the primary coil.
• The uses of step-up and step-down transformers
  in the National Grid.

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The motor effectNotes questions from pages 254
255

• What is the motor effect?
• Copy out the bullet points at the bottom of page
  254 listing the factors that affect the force on
  a current carrying wire inside a magnetic field.
• Copy and answer question (a) on page 254.
• Copy Figure 3 on page 255 and explain how a
  simple electric motor works. Your account should
  include the purpose of the split-ring commutator.
• Copy and answer question (b) on page 255.
• Copy Figure 4 on page 255 and explain how a
  moving coil loudspeaker works.
• Copy and answer question (c) on page 255.
• Copy the Key points table on page 255.
• Answer the summary questions on page 255.

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The motor effect ANSWERS

• In text questions
• No change, the actions cancel each other out.
• The material must conduct electricity.
• A direct current will not produce a changing
  magnetic field.

• Summary questions
• (a) Current, coil, force, coil.
• (b) Current, force, coil.
• 2. (a) The direction of the current is reversed
  and so the force on the coil is in the opposite
  direction.
• (b) (i) Faster because the coil is lighter
• (ii) Faster because the field is much stronger
  due to the presence of iron.

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Electromagnetic induction Notes questions from
pages 256 257

• What is induced in a wire because of the dynamo
  effect?
• Copy and answer question (a) on page 256.
• Copy Figure 2 on page 256 and explain how cycle
  dynamo works.
• Copy and answer questions (b) and (c) on page
  256.
• Explain how the alternating current generator on
  page 257 works. Your explanation should include a
  copy of both parts of Figure 4.
• Copy the Key points table on page 257.
• Answer the summary questions on page 257.

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Electromagnetic induction ANSWERS

• In text questions
• (a) (i) The current increases.
• (ii) The direction of the current reverses.
• (iii) No current is produced.
• The wires leading to the coil would get twisted
  up. No brushes are needed.
• (i) There is no current.
• (ii) A p.d. is produced in the opposite
  direction.

• Summary questions
• 1. (a) The pointer would move to the right but
  not as far.
• (b) The pointer returns to zero.
• (c) The pointer would move rapidly to the left.
• 2. (a) Spin the coil faster, use more loops of
  coil, use stronger magnets.
• (b) The peak voltage would be lower and the
  period would be longer.

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Transformers Notes questions from pages 258 259

• Copy Figure 1 on page 258 and (a) explain what a
  transformer is, (b) what a transformer does and
  (c) how a transformer works.
• Copy and answer questions (a), (b) and (c) on
  page 258.
• Copy the circuit symbol for a transformer on page
  259 and explain why the electric current supplied
  to a transformer must be alternating in order for
  the transformer to function.
• Copy and answer question (d) on page 259.
• Copy the Key points table on page 259.
• Answer the summary questions on page 259.

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Transformers ANSWERS

• In text questions
• The magnetic field in the core would be much
  weaker because the core is not a magnetic
  material.
• The lamp would be brighter.
• The lamp would not light up with direct current
  in the primary coil.
• Iron is easier to magnetise and demagnetise as
  the alternating current increases and decreases
  each half cycle.

• Summary questions
• 1. Current, primary, magnetic field, secondary,
  p.d., secondary.
• 2. (a) Direct current in the primary coil would
  not produce an alternating magnetic field, so no
  p.d. would be induced in the secondary coil.
• (b) The current would short-circuit across the
  wires instead of passing through them. This would
  cause the coil to overheat if it did not cause
  the fuse to blow.
• (c) Iron is a magnetic material, so it makes the
  magnetic field much stronger. It is easily
  magnetised and demagnetised when the current
  alternates.

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Transformers and the National Grid Notes
questions from pages 260 261

• (a) Why are transformers used in the National
  grid? (b) What is the advantage of using high
  voltages?
• Copy the transformer equation on page 260.
• Copy a version of the worked example on page 260
  but in your version change the number of turns on
  the secondary coil from 60 to 30.
• What is the purpose of (a) step-up and (b)
  step-down transformers?
• Explain how the number of turns on the coils of a
  transformer determine whether a transformer is
  step-up or step-down.
• State how the currents and voltages associated
  with the primary and secondary coils are related
  to each other with a 100 efficient transformer.
• Copy and answer questions (a) and (b) on page
  261.
• Copy the Key points table on page 261.
• Answer the summary questions on page 261.

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Transformers and the National Grid ANSWERS

• In text questions
• 60 turns
• (i) 6A (ii) 0.26A

• Summary questions
• 1. (a) (i) Secondary, primary.
• (b) Up, down.
• 2. (a) 2000 turns
• (b) (i) 3A (ii) 0.15A

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More power to you Notes questions from pages 262
263

• Answer questions 1 and 2 on page 263.

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More power to you ANSWERS

• (a) They would not need heavy iron magnets.
• (b) There would be no power wasted in the wires,
  as the wires would have no resistance.
• 2. (a) Ionising radiation, carcinogenic
  (cancer-causing) substances.
• (b) People are at risk due to other causes.
  There is an extra risk to those exposed to these
  magnetic fields.
• (c) A hypothesis is put forward as an unproven
  theory to be tested by scientific experiments. If
  lots of experiments are carried out and they all
  support the hypothesis, it gains scientific
  credibility and is accepted as a theory. But at
  any stage, it could be overthrown by any
  conflicting scientific evidence.

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How Science Works ANSWERS

• 0.01V
• Not at the greater heights.
• Improve the sensitivity of the oscilloscope.
  Repeat his results.
• By checking it against other data/other similar
  research/get someone else to repeat his work or
  calculate theoretical relationships.
• For example Measuring the speed of an object
  through a tube.

• The voltmeter was not sensitive enough. It would
  also not give a read-out of the voltage, so it
  would be impossible to get an accurate result
  even if it was sensitive enough.
• Height on the X-axis, voltage on the Y-axis. Axes
  fully labelled and plots correctly plotted.
• In part. The voltage increased as height
  increased, but it was not directly proportional.