Physics · Refraction of light at plane and spherical surfaces, thin lens formula and lens maker formula
The near point and far point of a person are and respectively. Determine the pow
The near point and far point of a person are \( 40 \mathrm{cm} \) and \( 250 \mathrm{cm} \) respectively. Determine the power of the lens he/she should use while reading a book kept at distance \( 25 \mathrm{cm} \) from the eye.
- A. 2 .5 D
- B. 5.0 D
- C. 1 .5 \)
- D. 3.5
Step-by-step solution
The person's near point is 40 cm, so to read at 25 cm, a converging lens is needed to form a virtual image at the near point. Using the lens formula with u = -25 cm and v = -40 cm, we get 1/f = 1/v - 1/u = 1/(-40) - 1/(-25) = -1/40 + 1/25 = 3/200 cm^-1. Thus f = 200/3 cm = 2/3 m, and power P = 1/f = 1.5 D.
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