Summary
Highlights
Transformers change the potential difference of electricity. There are two main types: step-up and step-down, used in the National Grid. Both consist of two coils of wire around an iron core.
In a step-up transformer, voltage is increased, with fewer turns on the primary coil than the secondary. In a step-down transformer, voltage is decreased, with more turns on the primary coil than the secondary.
Transformers work via electromagnetic induction. An AC current in the primary coil generates an alternating magnetic field in the iron core, which then induces a potential difference in the secondary coil at the same frequency. This only works with AC current.
The potential difference can be calculated using the formula: (potential difference across primary coil) / (potential difference across secondary coil) = (number of turns on primary coil) / (number of turns on secondary coil). An example is provided to illustrate this.
Transformers are nearly 100% efficient, meaning power in equals power out. This provides another formula: (current in primary coil × potential difference across it) = (current in secondary coil × potential difference across it). An example calculation is shown.
Switch-mode transformers are found in laptop and mobile phone chargers. They operate at high frequencies (50-200 kHz) and consume very little power when the device is not plugged in.