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.
🧲 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.
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.