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Class 7 Science — Circuits and their components

Name the parts of a torch circuit and what each does, read a circuit diagram's symbols, tell a conductor from an insulator, and say when a lamp glows and when it does not.

Name: ________________________

Before you start

Take apart an incandescent torch lamp and look at what makes the light.

1234
  1. 1. Glass bulb
  2. 2. Filament
  3. 3. Metal case
  4. 4. Metal tip

The filament is the thin wire that gets hot and glows. The metal case and the metal tip are the lamp's two terminals, kept apart so they cannot touch. An LED lamp has no filament inside it — it makes light a different way.

  1. 1.An incandescent lamp is taken out of a circuit and put back with its two terminals the other way round. What happens?

    • a) It stays dark, because current can pass through it in one direction
    • b) It glows more brightly, because the current now runs the natural way
    • c) It glows dimly, because half the current is turned back
    • d) It glows just as before, because the circuit is still complete

  2. 2.Two or more electric cells joined cap-to-disc, so the positive terminal of one meets the negative terminal of the next, are together called what?

  3. 3.Match each part of a torch circuit to the job it does.

    • Electric cell
    • Switch
    • Filament
    • completes or breaks the circuit
    • a portable source of electrical energy
    • gets hot and glows to give light

  4. 4.A drawing that stands in for a real circuit, made out of the agreed symbols rather than pictures, has a two-word name. What is it?

  5. 5.Silver, copper and gold are the three best conductors. Why is the metal inside an electric wire usually copper?

    • a) Copper is easier to draw into a thin wire than any other metal
    • b) Copper costs less and there is plenty of it, and it conducts nearly as well
    • c) Copper is the one metal that conducts electricity
    • d) Silver and gold are insulators

  6. 6.Follow the current round a working torch circuit, starting at the positive terminal of the cell.

    • The positive terminal of the cell
    • The negative terminal of the cell
    • The filament of the lamp
    • The switch, closed to ON

  7. 7.In the symbol for an electric cell, one line is drawn long and one short. What does the long line stand for?

    • a) The negative terminal
    • b) The positive terminal
    • c) The amount of energy left in the cell
    • d) The wire leaving the cell

  8. 8.A torch is slid to OFF. What is true of its circuit while it sits like that?

    • a) It is closed, and the current is stored inside the cell
    • b) It is open, and the current takes a shorter path instead
    • c) It is closed, but the current is too weak to light the lamp
    • d) It is open — a gap is left that the current cannot cross

Answer key — Class 7 Science — Circuits and their components

  1. 1. d) It glows just as before, because the circuit is still complete
  2. 2.
    • battery
    • a battery
  3. 3. Electric cell → a portable source of electrical energy; Switch → completes or breaks the circuit; Filament → gets hot and glows to give light
  4. 4.
    • circuit diagram
    • a circuit diagram
    • the circuit diagram
  5. 5. b) Copper costs less and there is plenty of it, and it conducts nearly as well
  6. 6. 1. The positive terminal of the cell 2. The switch, closed to ON 3. The filament of the lamp 4. The negative terminal of the cell
  7. 7. b) The positive terminal
  8. 8. d) It is open — a gap is left that the current cannot cross