Science (086) — AI-generated practice question

Lens used: A concave lens (diverging lens) is used to correct myopia.

How it restores normal vision: The myopic person's far point is 2 m (not infinity), meaning the image of distant objects forms in front of the retina. A concave lens of suitable power diverges the incoming light rays before they enter the eye. This shifts the image of the distant object back onto the retina, restoring clear distant vision.

Power of the lens required:
$$P = \frac{1}{f} = \frac{1}{-2} = -0.5 \text{ D}$$

Source: Chapter 10, Section 10.2 – Defects of Vision and Their Correction

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• Examiners expect you to name the lens type, explain why it is used (image forms in front of retina), and state how it corrects the defect (diverges rays so image shifts back to retina).
• For 3 marks, mentioning the power calculation using the far point (f = −2 m) earns the third mark.
• Always use a negative sign for the concave lens focal length/power — this is a common error students make.