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

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

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

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

  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 color of the wire and the shape of the switch
    • c) The material of the wire and nothing else
    • d) The material, thickness and length of the wire, and how long the current flows

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

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

  5. 5.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

    • Dry cell
    • Rechargeable battery

  6. 6.Why does a lifting electromagnet on a crane suit a scrapyard better than an ordinary magnet would?

    • a) It picks up materials that are not magnetic
    • b) The operator can drop the load by switching the current off
    • c) It works without any electricity supply
    • d) It is lighter than an ordinary magnet of the same size

  7. 7.A nichrome wire in a circuit gets warm. What is happening inside it?

    • a) The current rubs against the sides of the wire, and friction warms it
    • b) The wire is absorbing heat from the air around it
    • c) The cell is hot, and the heat travels along the wire
    • d) The wire resists the flow of current, and that resistance turns some electrical energy into heat

  8. 8.In a dry cell, which part acts as the negative terminal?

    • a) The metal cap on top
    • b) The paste-like electrolyte
    • c) The carbon rod at the center
    • d) The zinc container

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

  1. 1. b) It can still contain acids and metals that may cause fires or harm the environment
  2. 2. d) South
  3. 3. d) The material, thickness and length of the wire, and how long the current flows
  4. 4. c) For a wire of the same size and length, nichrome offers higher resistance and so gives more heat
  5. 5. Dry cell → Single use; Rechargeable battery → Recharged and reused many times
  6. 6. b) The operator can drop the load by switching the current off
  7. 7. d) The wire resists the flow of current, and that resistance turns some electrical energy into heat
  8. 8. d) The zinc container