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Leaving Cert Physics: Refraction

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

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

OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

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

Refraction, Higher Level(8 marks)

Quick ones on Refraction.

(a)State Snell's law.
  1. For two given media, i divided by r is a constant
  2. For two given media, sin i divided by sin r is a constant
  3. For two given media, sin i multiplied by sin r is a constant
(b)Name one important application of total internal reflection.
  1. Photographic film in a camera
  2. Spectacle lenses correcting long sight
  3. Optical fibres carrying light signals
(c)Speed of light in a medium of refractive index 1.5 (c = 3.0 × 10⁸ m s⁻¹)?
  1. 2.0 × 10⁸ m s⁻¹
  2. 1.5 × 10⁸ m s⁻¹
  3. 4.5 × 10⁸ m s⁻¹
Show the answers

(a) For two given media, sin i divided by sin r is a constant

(b) Optical fibres carrying light signals

(c) 2.0 × 10⁸ m s⁻¹

Your turn: Higher Level questions on Refraction.

Higher Level

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

Every paper, year by year

YearWhere it came up
2026Q8
2025Q4, Q14(b)
2024Q6(g), Q13
2023Q6(e)
2022Q3
2021Q14(d)
2019Q12(c)
2018Q2, Q5(e)
2017Q11
2016Q5(c), Q11

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

More Refraction questions

Refraction, 3 marks

What conditions are needed for total internal reflection?

  1. Light must travel from a less dense to a denser medium and strike the boundary above the critical angle
  2. Light must travel from a denser to a less dense medium and strike the boundary below the critical angle
  3. Light must travel from a denser to a less dense medium and strike the boundary above the critical angle
Show the answer

Light must travel from a denser to a less dense medium and strike the boundary above the critical angle

Above the critical angle no light refracts out and it is all reflected back inside. This is how optical fibres and 45 degree prisms work.

Refraction, 3 marks

The critical angle for diamond is 24.4°. What is the refractive index of diamond?

  1. 1.10
  2. 2.42
  3. 0.41
Show the answer

2.42

n = 1 ÷ sin C = 1 ÷ sin 24.4° = 1 ÷ 0.413 = 2.42. (0.41 is sin C itself; 1.10 comes from using cos instead of sin.)

Refraction, 3 marks

Why does a cut diamond sparkle more than glass cut to the same shape?

  1. Its small critical angle traps light inside it
  2. Its large critical angle lets most light escape
  3. Diamond gives out its own light when it is cut
Show the answer

Its small critical angle traps light inside it

With C = 24.4°, most rays inside a diamond meet a face above the critical angle and are totally internally reflected before leaving through the top.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q9, Q11
2025Q3, Q9
2024Q6(j)
2023Q6(k), Q8, Q14(b)
2022Q2, Q6(d), Q13, Q14(b)
2021Q6(f), Q8
2019Q3, Q11
2018Q5(b), Q12(b)
2017Q7
2016Q2, Q7, Q11

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

More Refraction questions

Refraction, 3 marks

Light strikes glass with i = 50° and is refracted at r = 30°. Refractive index?

  1. 1.67
  2. 0.65
  3. 1.53
Show the answer

1.53

n = sin i ÷ sin r = 0.766 ÷ 0.500 = 1.53. 1.67 divides the angles themselves (50 ÷ 30), which is wrong.

Refraction, 3 marks

Define the critical angle.

  1. The angle of refraction when a ray enters glass from air at 45°
  2. The angle of incidence in the denser medium for which the angle of refraction is 90°
  3. The angle of incidence in the less dense medium at which all the light is absorbed
Show the answer

The angle of incidence in the denser medium for which the angle of refraction is 90°

Above the critical angle, light cannot leave the denser medium and total internal reflection happens.

Refraction, 2 marks

Which medical instrument uses total internal reflection in optical fibres?

  1. An endoscope
  2. A stethoscope
  3. An X-ray machine
Show the answer

An endoscope

An endoscope carries light into the body and an image back out along optical fibres, so doctors can see inside without surgery.

Other Physics topics

All of Leaving Cert Physics