Question

an object is kept at a distance of 18cm,20cm,22cm,30cm,from lens of power +5D.

(i)in which case would you get a magnified image.

(ii)which magnified imagecan be get on the screen

Answer 1

Power=+5D

so the lens is convex

P=1/f

f=1/5 m

f=20 cm

so in each case

1/v-1/u=1/f

1/v=1/u +1/f

v=uf/(u+f)

v=20u/(20+u)

now u varies from

-18,-20, -22,-30 cm

so,

v=-180 cm

if u=-18 cm

so, magnification is (v/u)=+10

similarly

v=+220 cm if u=-22 cm

so magnification (v/u)=-10

v=+60 cm ,if u=-30 cm

so magnification is (v/u)=-2

if u=-20 cm

v=infinity

so the magnification=-infinity

now magnification is positive in 1st case

where u=-18 cm

all the other images can be obtained on screen


this is your answer I hope so it may be help you

Answer 2

Explanation:

A}. (I). P = 1/f

f =100/5

f = 20 cm

Object at. 18 cm ,22cm , 30cm, image can be magnified

ii). At 22 cm and 30 cm ,image can be obtained on a screen