Ceist Eile

Ceist Eile is in development. Features, questions and prices may change while we refine it.

Subjects · Leaving Cert Physics & Chemistry

Leaving Cert Physics & Chemistry: Waves, interference & diffraction

How often Waves, interference & diffraction comes up on the Physics & Chemistry papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Waves, interference & diffraction, Higher Level(7 marks)

Quick ones on Waves, interference & diffraction.

(a)A sound of frequency 680 Hz travels at 340 m s⁻¹. Its wavelength?
  1. 2 m
  2. 0.5 m
  3. 231,200 m
(b)In a longitudinal wave, the particles of the medium vibrate…
  1. Only in circles
  2. At right angles to the direction of travel
  3. Parallel to the direction the wave travels
(c)What is diffraction?
  1. Spreading of a wave through a gap or around an edge
  2. Splitting of white light into colours
  3. Bending of a wave as it enters a new medium
Show the answers

(a) 0.5 m

(b) Parallel to the direction the wave travels

(c) Spreading of a wave through a gap or around an edge

Your turn: Higher Level questions on Waves, interference & diffraction.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q1(k)
2024Q1(f), Q1(g), Q1(h)
2023Q1(j), Q1(k)
2022Q1(h), Q6(b)
2021Q1(k), Q6(c)
2019Q6(c)
2018Q6(c)
2017Q1(f)
2016Q1(g), Q6(b)

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

More Waves, interference & diffraction questions

Waves, interference & diffraction, 2 marks

Which of these is a transverse wave?

  1. Sound in air
  2. Ultrasound in the body
  3. Light
Show the answer

Light

In a transverse wave the vibrations are at right angles to the direction of travel. All electromagnetic waves are transverse; sound and ultrasound are longitudinal.

Waves, interference & diffraction, 3 marks

Why is the interference of light taken as evidence that light is a wave?

  1. Light travels extremely fast, faster than particles
  2. Only waves can reinforce and cancel each other
  3. Light travels in straight lines, like all waves
Show the answer

Only waves can reinforce and cancel each other

Bright and dark fringes come from waves adding (in phase) or cancelling (out of phase). Streams of particles cannot cancel each other out.

Ordinary Level

Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q1(j), Q1(k), Q1(l)
2024Q1(d), Q6(b)
2023Q1(h), Q1(k)
2022Q1(d), Q1(g)
2021Q1(i), Q6(c)
2019Q1(g), Q1(h), Q1(i)
2018Q1(g), Q6(c)
2017Q1(f), Q6(d)
2016Q1(f)

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

More Waves, interference & diffraction questions

Waves, interference & diffraction, 2 marks

The frequency of a wave is?

  1. Distance between two crests next to each other
  2. Height of a crest above the rest position
  3. Number of waves passing a point per second
Show the answer

Number of waves passing a point per second

Frequency is measured in hertz (1 Hz = one wave per second). The distance between crests is the wavelength; the height of a crest is the amplitude.

Waves, interference & diffraction, 2 marks

Unit of frequency?

  1. Joule
  2. Hertz
  3. Metre
Show the answer

Hertz

1 hertz (Hz) is one complete wave per second. Wavelength is measured in metres; energy in joules.

Waves, interference & diffraction, 3 marks

A wave has frequency 50 Hz and wavelength 4 m. Its speed?

  1. 200 m/s
  2. 12.5 m/s
  3. 54 m/s
Show the answer

200 m/s

v = fλ = 50 × 4 = 200 m/s. Speed = frequency × wavelength for every kind of wave.

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry