How Transformers Work
Part of National Grid & Transformers · GCSE GCSE Physics revision
This deep dive covers How Transformers Work within National Grid & Transformers for GCSE Physics. Revise National Grid & Transformers in Extra Topics for GCSE Physics with 14 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 3 of 12
Practice
14 questions
Recall
12 flashcards
🧲 How Transformers Work
Figure 2: Transformer structure — AC in primary coil creates a changing magnetic field in the iron core, inducing a voltage in the secondary coil
A transformer consists of two coils of wire wrapped around a soft iron core. The input side is the primary coil and the output side is the secondary coil.
Step-by-Step: The Transformer Mechanism
- Alternating current (AC) flows through the primary coil
- The alternating current creates a changing magnetic field in the primary coil
- The soft iron core carries this changing magnetic field efficiently to the secondary coil
- The changing magnetic field in the secondary coil induces an alternating voltage (electromagnetic induction)
- The size of the induced voltage depends on the ratio of turns in each coil
Why AC, Not DC?
Transformers only work with alternating current. A direct current (DC) creates a constant magnetic field that never changes. A constant magnetic field cannot induce a voltage in the secondary coil — electromagnetic induction requires a changing field. This is why the National Grid uses AC throughout.
Quick Check: Why does the National Grid transmit electricity at high voltage rather than low voltage?
High voltage means low current (since P = IV, for same power, higher V means lower I). Power wasted in cables is P = I²R. Lower current means much less power wasted as heat in the transmission cables. This makes the system far more efficient.
Keep building this topic
Read this section alongside the surrounding pages in National Grid & Transformers. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for National Grid & Transformers
What is the function of a step-up transformer in the National Grid?
Explain why electricity is transmitted at high voltage and low current through the National Grid power cables.
Quick Recall Flashcards
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