Correcting myopia and hypermetropia: Class 10 practice
A myopic eye has a far point closer than infinity; a concave lens of focal length f = −(far point) corrects it. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Lens formula
- Power of a lens
The idea behind correcting myopia and hypermetropia
A myopic eye has a far point closer than infinity; a concave lens of focal length f = −(far point) corrects it. A hypermetropic eye has a near point beyond 25 cm; a convex lens forms the image of an object at 25 cm at the near point. Power P = 100/f (f in cm).
Step-by-step method
- Myopia: f = −far point; P = 100/f.
- Hypermetropia: use 1/f = 1/v − 1/u with u = −25 cm, v = −near point.
- Give the lens type and power in dioptres.
Worked example 1 (Basic)
A myopic person's far point is 60 cm. What lens corrects it?
- f = −60 cm
- P = 100/−60 = -1.67 D
- Answer: Concave lens, -1.67 D
Worked example 2 (Standard)
A myopic person's far point is 230 cm. What lens corrects it?
- f = −230 cm
- P = 100/−230 = -0.43 D
- Answer: Concave lens, -0.43 D
Worked example 3 (Challenge)
A hypermetropic person's near point is 50 cm. Find the corrective lens power.
- 1/f = 1/(−50) − 1/(−25)
- f = 50 cm
- P = 2 D
- Answer: Convex lens, +2 D
Common mistakes and misconceptions
- Using a convex lens for myopia
- Sign of u and v
Practice questions
- (Basic) A myopic person's far point is 300 cm. What lens corrects it?
- (Basic) A myopic person's far point is 120 cm. What lens corrects it?
- (Standard) A myopic person's far point is 280 cm. What lens corrects it?
- (Standard) A myopic person's far point is 200 cm. What lens corrects it?
- (Challenge) A hypermetropic person's near point is 160 cm. Find the corrective lens power.
- (Challenge) A hypermetropic person's near point is 60 cm. Find the corrective lens power.
Answer key with full working
- Q1: f = −300 cm → P = 100/−300 = -0.33 D → Answer: Concave lens, -0.33 D
- Q2: f = −120 cm → P = 100/−120 = -0.83 D → Answer: Concave lens, -0.83 D
- Q3: f = −280 cm → P = 100/−280 = -0.36 D → Answer: Concave lens, -0.36 D
- Q4: f = −200 cm → P = 100/−200 = -0.5 D → Answer: Concave lens, -0.5 D
- Q5: 1/f = 1/(−160) − 1/(−25) → f = 29.63 cm → P = 3.38 D → Answer: Convex lens, +3.38 D
- Q6: 1/f = 1/(−60) − 1/(−25) → f = 42.86 cm → P = 2.33 D → Answer: Convex lens, +2.33 D
Syllabus note
This skill is listed under "The Human Eye" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is correcting myopia and hypermetropia in?
"The Human Eye", Class 10 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.