| Transformers: Design & Use | Transformer - a device that can change the PD/voltage of an AC (step-up=increase, step-down=decrease)
DESIGN:
- 2 coils of wire: primary -from the AC input, secondary -from leading to the AC output
- The coils aren't electrically connected, but are wound around an iron core which is easily magnetised and can carry magnetic fields from the primary to secondary coil
HOW IT WORKS:
1) a primary voltage drives an AC through a primary coil
2) the primary coil current produces a magnetic field which changes the current changes
3) the iron core increases the strength of the magnetic field
4) the changing magnetic field induces a changing potential difference in the secondary coil
5) the induced potential difference produces an alternating current in the external circuit
NOTE: the ratio of coils in a transformer match the ratio of PD |
| Power Transmission | - The National Grid carries electricity around Britain
- The higher the current in a cable, the greater the energy transferred to the surroundings by heating
- This means that high currents waste more energy than low currents.
- To reduce energy transfers to the environment, the National Grid uses step-up transformers to increase the voltage from power stations to thousands of volts, which lowers the current in the transmission cables
- Step-down transformers are then used to decrease the voltage from the transmission cables, so it is safer to distribute to homes and factories
NOTE: The equation for power assumes the transformer is 100% efficient |
