Make a torch: open and closed circuits
Open up a torch and switch it on and off. Loosen a wire, add a second cell and try a broken bulb, and find out when current can flow and the bulb glows.
Core concept
In short: Connect a cell, wires and a bulb, and make the torch light up.
A bulb glows only when the circuit is closed: an unbroken loop from the cell, through the bulb and back
Topic: Electricity
A torch is a simple electric circuit: A complete loop that electricity flows around, from the cell through the bulb and back. All key words. Its cells (often called batteries) push electric current: The flow of electricity through a wire, measured in amperes (A). All key words round a loop of wires and metal strips, through the bulb and back to the cells. When the current passes through the bulb's thin wire (the filament), the filament gets so hot that it glows. Current can only flow if the loop is unbroken all the way round: this is a closed circuit. If there is a gap anywhere, the circuit is open and no current flows. A switch is just a safe way of making and breaking that gap. In this lab you can also find out what a loose wire, a broken bulb and a second cell do.
What you will learn
- Name the parts of a torch circuit: cells, switch, bulb and wires.
- Explain the difference between an open and a closed circuit.
- Explain how a switch turns a bulb on and off.
- Find faults in a circuit: a loose wire or a broken bulb.
Before you start
- Know that a torch needs cells (batteries) to work.
Materials
- A torch, two 1.5 V cells, a spare bulb
Equipment
- A screwdriver to open the torch (with an adult's help)
Procedure
- Switch the torch on and record the brightness.
- Switch it off and record.
- Switch it on with a loose wire and record.
- Put in a second cell and record.
- Put in a broken (fused) bulb and record.
How this simulation is simplified
- Each cell gives 1.5 V; two cells in a row give 3 V.
- The brightness is shown as 50% with one cell and 100% with two (a simple scale for this torch).