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Grades 7 and 8 Beginner About 15 min Version 1 Awaiting review Free

Lighting a bulb: a simple circuit

An electric current is a flow of charge around a circuit. A cell (battery) pushes the current from its positive terminal, through the wires and the bulb, and back to its negative terminal. The current can only flow if the circuit is a complete loop with no gaps. A switch makes a gap on purpose: closing it completes the circuit and the bulb lights; opening it breaks the circuit. Two cells joined in series push harder, so a bigger current flows and the bulb is brighter.

What you will learn

  • Build a complete circuit with a cell, switch and bulb.
  • Explain why a circuit must be complete for current to flow.
  • Describe the effect of adding another cell.

Before you start

  • Know that electricity can be dangerous and that mains sockets must never be used for experiments.

Materials

  • 1.5 V cells in holders
  • Connecting wires with crocodile clips

Equipment

  • Torch bulb (2.5 V) in a holder
  • Switch

Procedure

  1. Close the switch with one cell and record what happens to the bulb.
  2. Open the switch and record.
  3. Add a second cell, close the switch and compare the brightness.
  4. Break the wire and close the switch.

How this simulation is simplified

  • Each cell gives 1.5 V and the bulb has a resistance of 5 Ω; the wires have no resistance.
  • The bulb is fully bright at 0.6 A.