Question

plz answer as soon as possible

Answer 1

hey dear option A is correct

Answer 2

P = 1/ Focal length of lens

Persons near view is v = - 50 cm

least distance of distinct vision = -25 cm

By lens makers formula

1/f =1/-50 - ( 1/-25)

1/f = -1/50 + 1/25

1/f = -1/25 ( 1/2-1)

1/f = -1/25 ( 1-2/2)

1/f = -1/25 ( -1/2)

1/f = 1/25 × 1/2

f = 25 × 2

f = 50 cm

Power = 1/0.5 m = 10/5 = 2 D

To read near things to read book , newspaper , phone etc with 2 D lens

persons far point is 3 m

and focal length will be -3 m

Power of lens = 1/f

==> 1/-3

==> -0.33 D

To see star he needs the given converging lens of power -0.33 D.

"-" sign means : short sightedness

"+" sign means : long sightedness