eZine · Nigerian exams

Refraction of light through plane and curved surfaces

JAMB Physics topic guide with 2 practice questions.

What to revise

  • laws of refraction; explanation in terms of velocity of light in the media
  • refractive index; determination for glass and liquid using Snell's law
  • real and apparent depth; lateral displacement
  • critical angle and total internal reflection
  • glass prism: minimum deviation formula
  • types of lenses
  • lens formula (1/f = 1/u + 1/v) and Newton's formula (f² = ab)
  • magnification

You should be able to

  • interpret the laws of refraction
  • determine the refractive index of glass and liquid using Snell's law
  • determine the focal length of curved surfaces
  • determine refractive index using real and apparent depth
  • determine the conditions for total internal reflection
  • examine the use of periscope, prism, binoculars and optical fibre
  • apply total internal reflection to the formation of mirage
  • use the lens formula and ray diagrams to solve optical problems
  • determine the magnification of an image
  • calculate the refractive index of a glass prism using the minimum deviation formula
  • trace rays through an optical prism

From JAMB's Physics syllabus official. Full syllabus →

eZine's published bank has 10 questions on this topic (counted 29 October 2026).

Practice questions

Question 1 · Refraction of light through plane and curved surfaces

A ray of light passes from air into a glass block. The angle of incidence is 45° and the angle of refraction is 30°. The refractive index of the glass is

Show answer and explanation

Answer: D. 1.41

n = sin i/sin r = sin 45°/sin 30° = 0.707/0.5 = 1.41. 1.50 is the ratio of the angles (45/30); 0.71 inverts the sines; 1.22 uses the ratio of cosines (cos 30°/cos 45°).

eZine practice question (original, teacher-reviewed)

Question 2 · Refraction of light through plane and curved surfaces

For a converging lens, an object is 9 cm from the principal focus on one side and its real image is 16 cm from the principal focus on the other side. The focal length of the lens is

Show answer and explanation

Answer: A. 12 cm

Newton's formula: f^2 = ab = 9 × 16 = 144, so f = 12 cm. 25 cm adds a and b; 144 cm forgets the square root; 12.5 cm averages a and b.

eZine practice question (original, teacher-reviewed)

Practise more Refraction of light through plane and curved surfaces questions with explanations.

Practise free →