The full-scale diagram below shows a converging lens and an object. Each principal focus is marked with an F:

Full-scale diagram showing a converging lens and an object with each principal focus marked with an F
  1. Draw two rays to find the position of the image. Label the image I. Draw arrows on each ray to show its direction.
  2. The magnification of an image, M, is defined by the equation: \frac{\text{height of image}}{\text{height of object}}. Calculate the magnification of the image in your ray diagram. Show your working out clearly.
  3. Is the image real or virtual? Explain your answer.
  4. State an application for a lens in this way.
Answer to question


  • Height of object = 1.6 cm
  • Height of image = 2.5 cm
  • M = \frac{\text{height of image}}{\text{height of object}}
  • M = \frac{\text{2.5 cm}}{\text{1.6 cm}}
  • M = 1.6
  • The magnification is 1.6.

3. The image is real. Actual rays of light pass through the image. It can be projected on a screen.

4. The image is real, inverted and enlarged. An application for a lens used in this way is a cinema projector.

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