Experiment Without a Fuse

• A simple experiment to demonstrate what happens if a circuit doesn’t contain a fuse provides a base understanding of the important of a fuse for elementary students. Connect a small 1.5-volt flashlight bulb to a regular AA battery; AA batteries produce 1.5 volts. The light illuminates perfectly. Now connect the same bulb to battery that produces more than 1.5 volts. A good battery to use is the 9-volt PP3 type that is used in smoke detectors; they are the ones that are rectangular in shape and have the two terminals on the top. As soon as the two wires connect to the battery you see a flash and the light blows. Explain that while a light bulb isn’t particularly expensive, if the same occurred for something far more expensive, it would be ruined. A fuse that costs a few cents would have stopped that happening, because it would have blown first.
  
  

What Is a Fuse?

• To understand the purpose of a fuse in electrical circuits, elementary students need to understand what a fuse is and what happens to a fuse to make it blow. Use this simple experiment to demonstrate what a fuse does. Cut a 4-inch strip of fuse wire rated to 500 milliamps. Amperes or milliamps are the current that flows through an electrical circuit. Twist one end of the wire around one of the terminals on a 9-volt PP3 battery. Hold the other end using a pair of long-nosed pliers. Touch the end of the fuse wire onto the other battery terminal and watch closely. You see the wire start to glow orange, then red and then the wire breaks. This replicates what a fuse does if too much current is flowing through a circuit or a short circuit occurs.
  
  

Fused Experiment

• Link a 2-inch strip of fuse wire that is rated up to 250 milliamps between the wire strip that’s connected to the “+” terminal on the 9-volt battery and the terminal on the bulb. Ensure the wire is disconnected from the battery first. Connect the wire back onto the battery terminal. This time the fuse wire breaks before the light bulb can blow. Explain that the resistance in the fuse wire was less than the bulb filament and therefore the fuse wire broke before the bulb had a chance to illuminate and subsequently blow.
  
  

Identify Different Fuse Ratings

• Now that your students understand fuses and their purpose, get the students to identify different fuses and the fuse ampere rating. Look on the underside of plugs connected to various electrical appliances to find the fuse needed. Notice that the rating of the fuse needed is different, depending on the type of electrical appliance. For example, a table lamp or similar item is likely to have a low rating of between 3 and 5 amperes, because the current required to light the lamp is small. However an item like a convection heater uses much more current, so the fuse rating is likely to be between 13 and 15 amperes.