Burglar Alarm

Objectives

• Describe the components required to complete an electric circuit.

Materials

• Per Class:
  tape
  wire cutters
  wire strippers

• Per student:
  baggie or small paper bag
  D-cell battery
  paper plate
  clothespin
  2 pieces of aluminum foil
  1 Christmas tree mini-light bulb with wires attached, ends stripped of insulation
  20 cm length of insulated wire, ends stripped of insulation
  small piece of cardboard
  30 cm length of fishing line

Key Questions

• What will happen to the light if someone steals your item?
• What is preventing the light bulb from switching on?
• What other materials could be used in place of the piece of cardboard?
• Are these materials conductors or insulators?

What To Do

Preparation:

1. Put together a kit of supplies in a baggie for each student.

Instructions:

1. Tape the battery to the plate.
2. Wrap aluminum foil around each leg of the clothespin.
   
3. Tape the one end of the light bulb’s wire to one leg’s foil and one end of the length of wire to the other.
4. Tape the free end of the length of wire to one battery terminal, and the free end of the light bulb’s wire to the other terminal.
5. Make sure the light comes on.
6. Tape one end of the fishing line to the piece of cardboard and put the cardboard between the legs of the clothespin. The light should go out.
   
7. Tape the other end of the fishing line to something precious and watch what happens if someone tries to steal it.
   

Extensions

• To make your burglar alarm closer to the real thing, you could replace the light bulb with a buzzer.
• Smoke alarms work in a very similar way to burglar alarms. Take one apart and see if you can identify all the parts of the circuit. Compare the inside to your burglar alarm.