Solutions: Medical Option - the EYE


(a) The diverging lens in the figure below forms an image of the object.

Complete the figure by drawing a ray diagram to show the formation of the image. Label the image.

  • ray diverging from F
  • ray through centre of lens to form labelled image

(2 marks)

(b) A diverging spectacle lens of power –3.0 D is used to correct a defect of vision. When used to view a real object, the image is formed 0.21 m from the lens.

(i) State the defect of vision.

Myopia or short sight

(ii) Calculate the distance of the object from the lens.

The image seen when wearing spectacles is on the same side of the lens as the onject and is upright - it is therefore virtual and you have to have a negative sign for 'v'.

P = 1/f = 1/u + 1/v

-3.0 = 1/u - 1/0.21

1/u = 1/0.21 - 3.0 = 1.76

u = 0.57 m

(3 marks)

(Total 5 marks)