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Electromagnetic induction and transformers
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Moving a wire through a magnetic field can create a potential difference. This is how power stations generate electricity.
Inducing a p.d.
When a wire moves through a magnetic field, or a magnetic field changes around a coil, a potential difference is induced.
If the circuit is complete, a current flows.
A bigger p.d.: move faster, use a stronger magnet, or use more turns of wire.
If the circuit is complete, a current flows.
A bigger p.d.: move faster, use a stronger magnet, or use more turns of wire.
Generators and the National Grid
Generators rotate a coil in a magnetic field (or a magnet in a coil) to induce an alternating p.d.
The National Grid uses step-up transformers to raise the p.d. to very high values for transmission. A high p.d. means a low current, so less energy is wasted heating the cables.
Step-down transformers lower the p.d. for homes.
The National Grid uses step-up transformers to raise the p.d. to very high values for transmission. A high p.d. means a low current, so less energy is wasted heating the cables.
Step-down transformers lower the p.d. for homes.
Transformer equations
A transformer has two coils on an iron core. It only works with a.c.
V_p ÷ V_s = N_p ÷ N_s (Higher).
For a 100% efficient transformer: V_p × I_p = V_s × I_s.
V_p ÷ V_s = N_p ÷ N_s (Higher).
For a 100% efficient transformer: V_p × I_p = V_s × I_s.
A transformer has 200 turns on the primary and 50 on the secondary. The input is 240 V. Find the output p.d.
- V_s = V_p × N_s ÷ N_p
- V_s = 240 × 50 ÷ 200
Answer: 60 V
Moving a wire in a field, or changing the field, induces a p.d. Step-up transformers reduce current in the grid so less energy is lost. V_p/V_s = N_p/N_s and V_p I_p = V_s I_s.
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