A transformer is a device that converts one AC voltage to another. A detailed description of how they work is given under transformer. The purpose of this page is to give details of how a demonstration transformer can be made very simply in a classroom in order to teach the basic principles. Demonstrations similar to this are usually performed in schools.

 

 

 

 

 

 

 

 

 

 

 

 

 

The Primary Circuit

 

An alternating current is needed for the primary circuit. A wall socket would suffice. To access its current, you can use an old lamp cord. To make the circular circuit, you'd need to separate the two wires of the lamp cord. One of the free ends is then wrapped around the magnetizable material. A large bolt or screwdriver can be used. To make sure the metal is magnetizable, test to see if a kitchen magnet sticks to it.

Once one end is coiled around the screwdriver or bolt, it can be attached to the other wire of the cord to complete the loop (see diagram). In fact, if you plug it in now, the screwdriver/bolt should work as an electromagnet.

Warning: Make sure the wire is coated all along the circuit. Bare wire should be covered with electrical tape. You don't want to risk a short or a shock. Also, the coil won't work right if it's wound with bare wire.

The Secondary Circuit

 

Use another wire for the secondary circuit. The wire should be coated for the same reasons the primary is. Coil the secondary wire around the bolt or screwdriver. Then attach the bare ends of the wire to the two terminals of a light bulb. (The two terminals of a light bulb are the metal screw threading and the metallic tip.)

Electrical tape may be needed to avoid crossing bare wires.

The transformer is now complete. You can insert the plug of the primary circuit into a wall socket after a last-minute check for overlapping bare wiring. If you smell any burning, remove the plug immediately. Either bare wires are crossed or another resistor needs insertion, for example, a light bulb in the primary circuit.

Changing the Bulb Brightness

 

Changing the number of windings per coil will change the voltage ratio between circuits. The more windings the secondary circuit has compared to the primary, the greater the voltage and the lesser the current of the secondary circuit. Since power lost through a resistor equals current-squared times resistance, the bulb can be made to brighten by lowering the voltage and increasing the current, that is, by increasing the secondary winding count.