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Year 9 Science — Magnetic and heating effects of current

Explain how a current makes a magnet and how it makes heat, and say what changes the strength of an electromagnet.

Name: ________________________

  1. 1.In the lemon cell built in the chapter, what plays the part of the electrolyte?

    • a) The LED
    • b) The iron nail
    • c) The lemon juice
    • d) The copper wire

  2. 2.A compass needle beneath a wire deflects when the switch is closed and returns when it is opened. What does the return show?

    • a) The compass needle has been demagnetised by the current
    • b) The current keeps flowing for a while after the switch is opened
    • c) The magnetic field disappears when the current stops flowing
    • d) The wire has become a permanent magnet

  3. 3.The chapter lists what the heat generated in a wire depends on. Which list is right?

    • a) The temperature of the room the circuit is in
    • b) The colour of the wire and the shape of the switch
    • c) The material, thickness and length of the wire, and how long the current flows
    • d) The material of the wire and nothing else

  4. 4.Match each change you could make to an electromagnet with what it does.

    • Adding a second cell to the circuit
    • Winding more turns onto the coil
    • Reversing the direction of the current
    • Pulling the iron nail out of the coil
    • a weaker magnet, since the core is gone
    • a stronger magnet without changing the current
    • a larger current, so a stronger magnet
    • the North and South ends swap over

  5. 5.Why should a used battery go to an e-waste facility rather than into the household bin?

    • a) It can still contain acids and metals that may cause fires or harm the environment
    • b) Household bins are too small for batteries
    • c) It will start working again once it has been sorted
    • d) A used battery is completely inert and so has no value

  6. 6.Match each part of a Voltaic cell to what it is.

    • Electrodes
    • Electrolyte
    • A dead cell
    • the liquid they are dipped in, usually a weak acid or salt solution
    • two metal rods of different materials
    • one whose chemicals have been used up, so it supplies no more electricity

  7. 7.The north pole of a magnetic compass is attracted towards end A of an electromagnet. Which pole is end A?

    • a) South
    • b) Neither — an electromagnet has no poles
    • c) North
    • d) Both at once

  8. 8.Nichrome, rather than copper, is used in electric heating devices. Why?

    • a) Nichrome conducts electricity better than copper
    • b) For a wire of the same size and length, nichrome offers higher resistance and so gives more heat
    • c) Nichrome is cheaper than copper
    • d) Nichrome does not conduct electricity

Answer key — Year 9 Science — Magnetic and heating effects of current

  1. 1. c) The lemon juice
  2. 2. c) The magnetic field disappears when the current stops flowing
  3. 3. c) The material, thickness and length of the wire, and how long the current flows
  4. 4. Adding a second cell to the circuit → a larger current, so a stronger magnet; Winding more turns onto the coil → a stronger magnet without changing the current; Reversing the direction of the current → the North and South ends swap over; Pulling the iron nail out of the coil → a weaker magnet, since the core is gone
  5. 5. a) It can still contain acids and metals that may cause fires or harm the environment
  6. 6. Electrodes → two metal rods of different materials; Electrolyte → the liquid they are dipped in, usually a weak acid or salt solution; A dead cell → one whose chemicals have been used up, so it supplies no more electricity
  7. 7. a) South
  8. 8. b) For a wire of the same size and length, nichrome offers higher resistance and so gives more heat