Lighting a bulb: a simple circuit
Connect cells, a switch and a bulb, close and open the switch, add a second cell and break a wire to see when current flows.
Core concept
Current flows only around a complete, unbroken circuit; more cells push a bigger current
Topic: Electricity
An electric current: The flow of electricity through a wire, measured in amperes (A). All key words is a flow of charge around a circuit: A complete loop that electricity flows around, from the cell through the bulb and back. All key words. 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
- Close the switch with one cell and record what happens to the bulb.
- Open the switch and record.
- Add a second cell, close the switch and compare the brightness.
- 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.