Question

HEY GUYS,PLZ ANSWER THIS QUESTION RIGHTLY,I'LL MARK IT BRAINLIEST:- An object is kept at a distance of 18cm,20cm22cm and 45cm respectively from a lens of power +5D. a)In which case or cases will you get a magnified image? b)Which of the magnified image can be obtained on 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