Question

A person cannot see objects nearer than 90cm . the power and nature of lens he should use to see object at 30 cm

Answer 1

Let the object distance be 90 cms and image distance be 30 cm

so by lens formula

1/f =1/v-1/u

1/f =1/30cm-1/-90cm

1/f = 1/30+1/90 (by taking LCM as 90

1/f = 4/90cm

f=90/4= 22.5cm =22.5/100m

P=1/f so

P = 100/22.5=4.44