Induction and transformers explains how a changing magnetic field produces a voltage, how that idea powers generators and transformers, and why electricity is sent over long distances at high voltage. It links the ideas from magnetism and fields with the circuit work you did earlier.
Exact wording and required items change between syllabus years, so check the current Cambridge IGCSE Physics 0625 page for your exam year. This page follows the general skills. The Physics learning guide shows where the topic sits in the whole subject.
What do I need to know first?
You need the basics of magnetic fields and field lines, and the electrical quantities current, voltage and power, with P = I × V. You also need to rearrange a simple equation and handle ratios. If those feel shaky, revisit magnetism and fields first.
One worked example that uses the whole topic
A fictional village is supplied by a power station that sends out 60 kW. (Invented example data.) The cables have a total resistance of 2.0 Ω.
Without a transformer: if the power is sent at 600 V, the current is 60 000 ÷ 600 = 100 A. Power lost in the cables = I² × R = 100² × 2.0 = 20 000 W, which is 20 kW, one third of the power.
With a step-up transformer: raise the voltage to 6000 V. The current falls to 60 000 ÷ 6000 = 10 A. Power lost = 10² × 2.0 = 200 W.
What changed? The voltage rose by a factor of 10, the current fell by a factor of 10, and the loss fell by a factor of 100. A transformer only works if the current in its primary coil keeps changing, which is why the supply is alternating current.
That one example touches induced voltage, the transformer ratio, alternating current and transmission loss. The lessons take each idea separately.
In what order should I study the lessons?
- Explain a change needed for induced voltage. Everything else depends on the idea that something must change.
- Compare generator and motor energy transfers. This applies induction in one direction and the motor effect in the other.
- Use a transformer ratio under stated assumptions. The equation comes next, once you know why it works.
- Explain why alternating current is relevant. This answers why transformers need a changing supply.
- Calculate a transmission loss in a fictional model. It combines the ratio, power and I² × R in one multi-step problem.
Then use the induction and transformers practice set to test all five together.
What traps catch students?
- Induced voltage with no change. A magnet sitting still in a coil induces nothing.
- Turning the ratio upside down. Step-down means fewer turns on the secondary.
- Saying a transformer works on a battery. A steady current gives no changing field.
- Using V² ÷ R for cable loss. The voltage across the cable is not the supply voltage.
- Saying a generator makes energy. It transfers it.
How do I use the practice set well?
Attempt it after the lessons, with units in every line of working. Check the worked answers, then use the table at the end to send each error type back to its lesson. A mistake log and retest queue helps you keep track of repeated slips.
Induction questions reward clear reasoning in words as much as correct arithmetic. That combination is what our teachers work on in online one-to-one Physics tuition.