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Subjects · Leaving Cert Physics

Leaving Cert Physics: Transformers

How often Transformers comes up on the Physics papers, every year it was asked, and questions to try.

HL Asked on 4 of the last 10 Higher Level papers, most recently in 2025.

OL Asked on 2 of the last 10 Ordinary Level papers, most recently in 2025.

June 2027 is the first exam on the new Physics course. These come from the 2016–2026 papers, so read them as a guide.

Transformers, Higher Level(8 marks)

Quick ones on Transformers.

(a)Transformer equation linking the voltages and the numbers of turns?
  1. Vs/Vp = Np/Ns
  2. Vs/Vp = Ns/Np
  3. Vs × Vp = Ns × Np
(b)A transformer has 200 turns on the primary and 1000 on the secondary. Output for a 230 V input?
  1. 1000 V
  2. 46 V
  3. 1150 V
(c)A transformer takes in 500 W and delivers 460 W. What is its efficiency?
  1. 92%
  2. 109%
  3. 8%
Show the answers

(a) Vs/Vp = Ns/Np

(b) 1150 V

(c) 92%

Your turn: Higher Level questions on Transformers.

Higher Level

Asked on 4 of the last 10 Higher Level papers, most recently in 2025.

Every paper, year by year

YearWhere it came up
2026Not asked
2025Q13
2024Q9
2023Not asked
2022Not asked
2021Not asked
2019Q11
2018Not asked
2017Not asked
2016Q5(g)

Links open the State Examinations Commission’s paper for that year.

More Transformers questions

Transformers, 3 marks

Why does a transformer work with ac but not with steady dc?

  1. Direct current has too high a voltage for the primary coil to carry
  2. Alternating current carries more charge through the coils each second
  3. A changing current is needed to give a changing flux, which induces an emf
Show the answer

A changing current is needed to give a changing flux, which induces an emf

Faraday's law needs a changing flux. A steady dc current gives a steady flux, so no emf is induced in the secondary coil.

Transformers, 3 marks

What causes eddy current losses in a transformer and how are they reduced?

  1. Resistance of the copper coils, reduced by using thicker wire
  2. Currents induced in the core itself, reduced by laminating the core
  3. Friction between the coils and the core, reduced by using oil
Show the answer

Currents induced in the core itself, reduced by laminating the core

The changing flux induces currents in the iron core, wasting energy as heat. Thin insulated laminations break up the paths these currents can take.

Transformers, 2 marks

What causes most of the energy loss in National Grid cables?

  1. Heating of the cables by the current (I²R)
  2. Magnetic flux leaking out of the cables
  3. Charge leaking out of the cables into the ground
Show the answer

Heating of the cables by the current (I²R)

Power lost = I²R. Stepping the voltage up makes the current small for the same power, so the heating losses fall dramatically.

Ordinary Level

Asked on 2 of the last 10 Ordinary Level papers, most recently in 2025.

Every paper, year by year

YearWhere it came up
2026Not asked
2025Q10
2024Not asked
2023Not asked
2022Not asked
2021Not asked
2019Not asked
2018Not asked
2017Not asked
2016Q5(g)

Links open the State Examinations Commission’s paper for that year.

More Transformers questions

Transformers, 2 marks

What does a step-down transformer do?

  1. Increases an ac voltage
  2. Changes ac into dc
  3. Reduces an ac voltage
Show the answer

Reduces an ac voltage

A step-down transformer has fewer turns on the secondary coil than the primary. Phone chargers use one to lower 230 V.

Transformers, 3 marks

A transformer steps 230 V down to 23 V. The primary coil has 1000 turns. Turns on the secondary?

  1. 10
  2. 100
  3. 10 000
Show the answer

100

Vs/Vp = Ns/Np, so Ns = 1000 × 23 ÷ 230 = 100 turns. The voltage falls by 10 times, so the turns do too.

Transformers, 3 marks

A transformer takes in 200 W and gives out 190 W. What is its efficiency?

  1. 95%
  2. 5%
  3. 105%
Show the answer

95%

Efficiency = output ÷ input × 100 = 190 ÷ 200 × 100 = 95%. The other 10 W is lost as heat in the coils and core.

Other Physics topics

All of Leaving Cert Physics