Question

After a check up, a person now has a far point of 100 cm, but with good near point vision. He needs to wear a new pair of corrective glasses. He accidentally takes his old contact lenses with him while traveling. If the lenses of the old pair have a power of -0.5 diopters, what is his far point (measured from his eye) when he is wearing the old lenses?

Answer 1

Answer:

so his far point according to this pair of glass is 200 cm

Explanation:

power of old pair of corrective glasses is given as

$P = -0.5 dioptre$

now we have

$f = \frac{1}{P}$

$f = -2 m$

$f = -200 cm$

now we know that for normal vision the maximum distance of vision is for infinite distance

so by lens formula we have

$\frac{1}{d_i} + \frac{1}{d_o} = \frac{1}{f}$

$\frac{1}{d_i} + 0 = \frac{1}{200}$

$d_i = 200 cm$

so his far point according to this pair of glass is 200 cm