← Back to the activity

Grade 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.Why are the plug tops, switch covers and wire coverings in a house made of rubber, plastic or ceramic?

    • a) They are cheaper to make than the metal parts underneath
    • b) They are conductors, so they carry the current away from a person
    • c) They stop the metal underneath from rusting
    • d) They are insulators, so they keep the current from reaching a person

  2. 2.Each of these was held across the two free ends of a tester's wires. Sort them by whether the lamp glowed.

    Groups: Conductor · Insulator

    • Aluminum foil
    • Metal key
    • Rubber eraser
    • Wooden stick
    • Copper wire
    • Plastic scale

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

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

  4. 4.This is the circuit diagram of a torch. Tap the symbol for the switch.

    Write the number of the part.

    123

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

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

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

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

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

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

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

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

Answer key — Grade 7 Science — Circuits and their components

  1. 1. d) They are insulators, so they keep the current from reaching a person
  2. 2. Copper wire → Conductor; Metal key → Conductor; Aluminum foil → Conductor; Plastic scale → Insulator; Rubber eraser → Insulator; Wooden stick → Insulator
  3. 3. 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
  4. 4. 3 — Switch
  5. 5. Electric cell → a portable source of electrical energy; Switch → completes or breaks the circuit; Filament → gets hot and glows to give light
  6. 6. d) It is open — a gap is left that the current cannot cross
  7. 7. d) It glows just as before, because the circuit is still complete
  8. 8. b) Copper costs less and there is plenty of it, and it conducts nearly as well