Higher tier: Transformers
Transformers are used to increase or decrease the voltage of alternating currents.
A transformer consists of three main parts:
- A primary coil.
- A secondary coil.
- An iron core on which the two coils are wound.
Types of transformer
Transformers are used to convert, or transform, voltages from low to high or high to low.
They only work with Alternating current occurs when electric charges continually change direction whilst moving through a conductor. Mains ac supply alternates with a frequency of 50Hz..
This has a similar role to the moving magnet or coil in a generator.
The size of the output voltage depends on the number of turns on the secondary compared to the primary coil.
There are two types of transformer:
- a step-up transformer, which steps-up voltage, has more turns in the secondary than in the primary;
- a step-down transformer, which steps-down voltage, has fewer turns in the secondary than in the primary.
The transformer in the diagram above is a step-down transformer – there are fewer turns on the secondary coil than on the primary coil.
| Type of transformer | Size of output voltage | Number of turns on the secondary compared to the primary |
| Step-up | increased | more |
| Step-down | decreased | fewer |
| Type of transformer | Step-up |
|---|---|
| Size of output voltage | increased |
| Number of turns on the secondary compared to the primary | more |
| Type of transformer | Step-down |
|---|---|
| Size of output voltage | decreased |
| Number of turns on the secondary compared to the primary | fewer |
Question
The primary coil of a An electrical device that increases, or decreases, the voltage (p.d.) of an alternating current. has 1,000 turns.
What type of transformer is it if the secondary coil has 500 turns?
The secondary coil has fewer turns than the primary coil and so this is a step-down transformer.
It will step-down voltage.