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Year 8 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.Sort these two kinds of cell by whether they can be used again after they run down.

    Groups: Single use · Recharged and reused many times

    • Rechargeable battery
    • Dry cell

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

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

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

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

  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 larger current, so a stronger magnet
    • the North and South ends swap over
    • a stronger magnet without changing the current

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

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

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

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

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

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

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

Answer key — Year 8 Science — Magnetic and heating effects of current

  1. 1. Dry cell → Single use; Rechargeable battery → Recharged and reused many times
  2. 2. d) It can still contain acids and metals that may cause fires or harm the environment
  3. 3. a) 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. d) South
  6. 6. b) The magnetic field disappears when the current stops flowing
  7. 7. a) The lemon juice
  8. 8. 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