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Leaving Cert Physics & Chemistry: EM spectrum & photoelectric effect

How often EM spectrum & photoelectric effect comes up on the Physics & Chemistry papers, every year it was asked, and questions to try.

HL Asked on 8 of the last 9 Higher Level papers, most recently in 2025. most years

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

EM spectrum & photoelectric effect, Higher Level(7 marks)

Quick ones on EM spectrum & photoelectric effect.

(a)Which radiation has a longer wavelength than visible light?
  1. Ultraviolet
  2. Infrared
  3. X-rays
(b)Energy of a photon of frequency 5.0 × 10¹⁴ Hz? (h = 6.6 × 10⁻³⁴ J s)
  1. 1.3 × 10⁻⁴⁸ J
  2. 3.3 × 10⁻²⁰ J
  3. 3.3 × 10⁻¹⁹ J
(c)In a vacuum, all electromagnetic waves travel at…
  1. 3.0 × 10⁸ m s⁻¹
  2. A speed that rises with frequency
  3. 340 m s⁻¹
Show the answers

(a) Infrared

(b) 3.3 × 10⁻¹⁹ J

(c) 3.0 × 10⁸ m s⁻¹

Your turn: Higher Level questions on EM spectrum & photoelectric effect.

Higher Level

Asked on 8 of the last 9 Higher Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025Q1(j), Q6(b)
2024Q1(e)
2023Q1(i), Q6(b)
2022Q1(i), Q1(k), Q6(b)
2021Q1(k), Q6(c)
2019Not asked
2018Q1(e), Q1(f), Q1(g)
2017Q1(e), Q6(b)
2016Q1(f)

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

More EM spectrum & photoelectric effect questions

EM spectrum & photoelectric effect, 2 marks

The frequency of a photon is doubled. Its energy…

  1. Halves
  2. Is four times bigger
  3. Doubles
Show the answer

Doubles

E = hf, and h is a constant, so photon energy is directly proportional to frequency. Double f gives double E.

EM spectrum & photoelectric effect, 2 marks

Which radiation do most TV remote controls use?

  1. Gamma rays
  2. Infrared
  3. Ultraviolet
Show the answer

Infrared

Remote controls send pulses of infrared, just beyond the red end of the visible spectrum. It is invisible to the eye but easily detected by a sensor.

EM spectrum & photoelectric effect, 2 marks

The photoelectric effect is the emission of electrons from a metal surface when…

  1. Light of high enough frequency falls on it
  2. It is heated strongly
  3. It is placed in a strong magnetic field
Show the answer

Light of high enough frequency falls on it

Each photon gives its energy to one electron. If the frequency is high enough, the electron escapes the surface. Emission by heating is a different effect.

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
2025Q6(c)
2024Q6(c)
2023Q1(g), Q1(j), Q6(d)
2022Q1(e), Q1(n)
2021Q1(l)
2019Q1(n), Q6(c)
2018Q1(m), Q6(c)
2017Q1(g), Q1(m), Q6(d)
2016Q1(g), Q6(d)

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

More EM spectrum & photoelectric effect questions

EM spectrum & photoelectric effect, 2 marks

Dispersion of light is?

  1. Spreading of a wave through a gap
  2. Bouncing of light off a mirror
  3. Splitting of white light into its colours
Show the answer

Splitting of white light into its colours

A prism refracts each colour by a different amount, giving red, orange, yellow, green, blue, indigo, violet. A rainbow is dispersion by raindrops.

EM spectrum & photoelectric effect, 2 marks

Which electromagnetic radiation has the longest wavelength?

  1. Ultraviolet
  2. Radio waves
  3. Gamma rays
Show the answer

Radio waves

Order by increasing wavelength: gamma, X-rays, UV, visible, infrared, microwaves, radio. Longest wavelength means lowest frequency.

EM spectrum & photoelectric effect, 2 marks

A blackened-bulb thermometer warms up just beyond the red end of a spectrum. Which radiation?

  1. Infrared
  2. Ultraviolet
  3. X-rays
Show the answer

Infrared

Infrared lies just past red and is absorbed as heat. Ultraviolet lies beyond violet, at the other end, and is detected by fluorescence.

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry