Purpose: Discuss how house fires happen and illustrate a common safety device used to prevent electrical fires — the fuse.
Materials:
- 6 Volt lantern battery or DC power supply
- balloon
- tinsel
- tape
- alligator clip wires (4)
- small 6V light bulb
- small light bulb holder
Procedure:
- Blow up balloon
- Tape a piece of tinsel across the balloon. Keep at least an inch of the tinsel free from the tape on both ends as shown in the diagram below.
- Make a complete series circuit including the tinsel (balloon fuse) and the light bulb by connecting the positive side of the battery to one end of the tinsel with the alligator clip. Then connect the other end of the tinsel to one end of the light bulb holder with the next alligator clip. Finally, with the third alligator clip connect the other end of the light bulb holder to the negative end of the battery.
- The light bulb should light showing that there is current going through the light bulb and the circuit.
- Take the last alligator clip and connect one end to one side of the light bulb holder and the other end to the other side.
- You have now created a short circuit, or an alternate path for the electricity to flow around the light bulb instead of through it.
- The balloon should burst almost immediately.
Explanation:
A short circuit allows a large amount of current to flow though a wire. As the amount of current increases, so does the temperature of the wire. The tinsel is the part that will heat up the quickest, as it heats up it melts a hole in the side of the balloon causing it to burst, just as a real fuse would melt and become disconnected as too much current flows through it.
Reinforcement Activities:
Take a piece of steel wool and place it across the two terminals of the 6.0 Volt battery, the steel wool will heat up and glow orange hot and eventually break, as the steel wool breaks it could fling in different directions, be sure to wear safety goggles, clear the area of anything flammable, and shield the students from any flying debris. This activity shows what happened to the tinsel in an amount of time in which the students can observe the wool heating up. Point out how short circuits can easily start electrical fires
A different and more common electrical home safety device would be a circuit breaker, which contains a bimetallic strip. The strip bends breaking the circuit when it heats up due to too much current flowing through the circuit breaker. The advantage of a circuit breaker over a fuse is that it does not need to be replaced every time it is blown. You can show students how a bimetallic strip works using an hairdryer.
