Exam questions on thin lenses

Exam questions on thin lenses often cover the properties of converging (convex) and diverging (concave) lenses. These questions include topics like image formation, focal length, magnification, and the thin lens equation. 

You face questions asking you to define key terms. They ask you to distinguish between real and virtual images. You can also be asked to apply the thin lens formula to calculate image distances, focal lengths, or magnification. Additionally, questions involve ray diagrams, understanding how lenses correct vision defects, or comparing lenses with mirrors. 

Here’s a breakdown of common question types:

• Definitions and Concepts
• Image Formation
• Thin Lens Equation and Calculations
• Applications and Comparisons
• higher order questions live derivation of equation

Examination Questions on thin lenses

1. Figure 10 below shows an object in front of a lens.

(i) Using rays locate the image of the object as seen by observer E.

(ii)Give one application of such a lens as used above.

(iii) Write three similarities between an eye and a camera

( b)   Figure 11 (a) and (b) show diagram the human eye

In figure 11 (a) sketch array diagram showing long sightedness

And In figure 11 (b) sketch array diagram showing how a lens is used to correct the long sightedness.

(c) A object of height 10.5 cm stands before a diverging lens of focal length 20 cm and a distance of 10cm from the lens. Find.

i)          Image distance

ii)         Height of the image

iii)        Magnification

2. A real object of height 1 cm placed 50 mm from a converging lens. It forms a virtual image 100 mm from the lens.

(i) Determine the:

(I) focal length of the lens ; (3 marks)

(II) magnification. (2 marks)

(ii) On the grid provided, draw to scale the ray diagram for the setup to show how the image is formed (3 marks)

3. Figure 8 shows an object O placed in front of a diverging lens whose principal focus is F.

on the figure , draw a ray diagram to locate the image formed (3 marks)

Question 4

17 (a) Figure 16 shows a graph of magnification against object distance for an object placed in front of a lens of focal length 20 cm.

Using the graph;

(i) State the effect on the size of the image when the object distance is increased from 25 cm. (1 mark)

(ii) Determine the distance between the object and the lens when the image is the same size as the object (2 marks)

(iii) Determine the image distance when the object distance is 25 cm. (3 marks)

Related topics

• Electromagnetic waves
• Thin Lenses