Transformers Investigation. Investigating how the number of secondary coils affects the voltage of the secondary in a transformer. The Equation There is a mathematical link between the number of turns and the voltages on each coil. A transformer is an electrical device that changes the voltage of an AC supply. A transformer changes a highvoltage supply into a low-voltage one, or vice versa. A transformer that increases the voltage is called a step-up transformer A transformer that decreases the voltage is called a step-down transformer Step-down transformers are used in mains adapters and rechargers for mobile phones and CD players. Equipment • • • • • 2 Iron C-cores Low voltage a.c. supply Voltmeter Red plastic coated wire Black plastic coated wire Method: 1. Wind a 30 coils of plastic wire around on of the C-cores. This is the primary coil. The number of coils on the primary will remain constant throughout the investigation 2. Wind 10 turns of plastic covered wire onto another C-core. This will be your secondary coil 3. Place the C-cores next to each other as shown in the diagram above 4. Attach the wires from the primary coil to a 2 volt alternating current supply 5. Attach the wires from the secondary coil to an alternating current voltmeter 6. Switch on the power supply and record the reading on the voltmeter 7. Repeat the above steps increasing the number of coils in the secondary by 10 each time up to a maximum of 60 turns.