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Leaving Cert Physics: Alternating current

How often Alternating current 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 2026.

OL Asked on 1 of the last 10 Ordinary Level papers, most recently in 2018.

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

Alternating current, Higher Level(8 marks)

Quick ones on Alternating current.

(a)Frequency of the mains ac supply in Ireland?
  1. 60 Hz
  2. 50 Hz
  3. 230 Hz
(b)Peak voltage of a 230 V rms mains supply?
  1. 460 V
  2. 163 V
  3. 325 V
(c)An ac supply has a peak voltage of 170 V. What is its rms voltage?
  1. 120 V
  2. 85 V
  3. 240 V
Show the answers

(a) 50 Hz

(b) 325 V

(c) 120 V

Your turn: Higher Level questions on Alternating current.

Higher Level

Asked on 4 of the last 10 Higher Level papers, most recently in 2026.

Every paper, year by year

YearWhere it came up
2026Q13
2025Q13
2024Not asked
2023Q6(i)
2022Not asked
2021Not asked
2019Not asked
2018Not asked
2017Q8
2016Not asked

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

More Alternating current questions

Alternating current, 3 marks

What does the rms value of an alternating voltage mean?

  1. The largest value that the voltage reaches during each full cycle
  2. The average value of the voltage taken over one full cycle
  3. The steady dc voltage that would give the same heating effect
Show the answer

The steady dc voltage that would give the same heating effect

Vrms = Vpeak divided by √2. The true average over a full cycle is zero, which is why rms is used. Mains is quoted as 230 V rms.

Alternating current, 3 marks

Why is ac rather than dc used to distribute electricity over the National Grid?

  1. It produces no heating at all in the cables
  2. Its voltage is easily stepped up and down by transformers
  3. It travels along cables faster than direct current
Show the answer

Its voltage is easily stepped up and down by transformers

Transformers need a changing current. Stepping up to high voltage lets the same power flow at a small current, which cuts the I²R heating losses in the cables.

Ordinary Level

Asked on 1 of the last 10 Ordinary Level papers, most recently in 2018.

Every paper, year by year

YearWhere it came up
2026Not asked
2025Not asked
2024Not asked
2023Not asked
2022Not asked
2021Not asked
2019Not asked
2018Q12(d)
2017Not asked
2016Not asked

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

More Alternating current questions

Alternating current, 2 marks

What is alternating current (ac)?

  1. A current that flows in one direction only
  2. A current that increases steadily
  3. A current that keeps reversing its direction
Show the answer

A current that keeps reversing its direction

Mains ac in Ireland goes through 50 complete cycles every second (50 Hz). A current in one direction only is dc, as from a battery.

Alternating current, 2 marks

Voltage of the mains supply in an Irish home?

  1. 50 V
  2. 230 V
  3. 12 V
Show the answer

230 V

Mains is 230 V ac at 50 Hz. 50 is the frequency in hertz, not the voltage.

Other Physics topics

All of Leaving Cert Physics