Extra TopicsHow It Works

The Transformer Equations

Part of National Grid & Transformers · GCSE GCSE Physics revision

This how it works covers The Transformer Equations 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 4 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 4 of 12

Practice

14 questions

Recall

12 flashcards

⚙️ The Transformer Equations

There are two key equations for transformers, both of which can appear in exam questions.

Turns Ratio Equation (Voltage Ratio)

V_p / V_s = N_p / N_s

Primary voltage / Secondary voltage = Primary turns / Secondary turns

V_p = primary (input) voltage in volts (V)
V_s = secondary (output) voltage in volts (V)
N_p = number of turns on primary coil
N_s = number of turns on secondary coil

Step-up transformer: N_s > N_p, so V_s > V_p — output voltage is higher than input voltage.

Step-down transformer: N_s < N_p, so V_s < V_p — output voltage is lower than input voltage.

Power Equation (100% Efficiency)

V_p × I_p = V_s × I_s

Power in = Power out (for an ideal 100% efficient transformer)

If voltage is stepped up, current is stepped down by the same factor, keeping power constant (in an ideal transformer). If voltage doubles, current halves.

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.

How Transformers Work Worked Examples The Cleverest Solution in Engineering History How the National Grid Works

Practice Questions for National Grid & Transformers

What is the function of a step-up transformer in the National Grid?

A. To increase current and decrease voltage for transmission
B. To increase voltage and decrease current for transmission
C. To convert AC to DC for transmission
D. To store electrical energy during low-demand periods

1 markfoundation

Explain why electricity is transmitted at high voltage and low current through the National Grid power cables.

3 marksstandard

Quick Recall Flashcards

What voltage do homes receive?

230 V

How does a transformer work?

AC in primary creates changing magnetic field → iron core transfers field to secondary → changing field induces voltage in secondary (electromagnetic induction)

14 questions on National Grid & Transformers — practise free

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How Transformers Work

Worked Examples