Power of a Lens MCQs

Q1. A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

• A.i) 0.18 m, ii) 0.67 m
• B.i) 0.18 m, ii) 0.67 cm
• C.i) 0.18 cm, ii) 0.67 m
• D.i) 0.67 m, ii) 0.18 m

Answer: A. i) 0.18 m, ii) 0.67 m

Q2. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

• A.The focal length is 66.67 cm and the lens is converging
• B.The focal length is 33.33 cm and the lens is converging
• C.The focal length is 66.67 cm and the lens is diverging
• D.The focal length is 33.33 cm and the lens is diverging

Answer: A. The focal length is 66.67 cm and the lens is converging

First, read what's there - a typical physics numerical. The data on the table: 1.5. We are after Find the focal length of the lens. Pick the chapter relation that contains every given quantity and the unknown; rearrange for the unknown. Common-sense check: The focal length is 66.67 cm and the lens is converging. Lock in option A) The focal length is 66.67 cm and the lens is converging. Trap-watch: option B) 'The focal length is 33.33 cm and the lens is converging' is wrong because This is not the correct solution; option C) 'The focal length is 66.67 cm and the lens is diverging' is wrong because This is not the correct solution.

Q3. A person cannot see nearby objects clearly (hypermetropia). Which type of lens is used in spectacles to correct this defect?

• A.A convex (convergent) lens
• B.A concave (divergent) lens
• C.A cylindrical lens
• D.A plane mirror

Answer: A. A convex (convergent) lens