Question

the image of an object placed at 60cm in front of a lens is obtained on a screen at a distance of 120cm from it. find the focal lenght of the lens . what would be the height of the image if the height of the object is 5cm?

Answer 1

hii mate!!

Object distance u = -60 cm
Image distance v = +120 cm
Using lens formula, 1/f = 1/v - 1/u
1/f = 1/120 - ( -1/60 ) = 1/120 + 1/60 = 3/120 = 40 
f = +40 cm
H(image) / H(object) = v/u
Hi = -120/60 X 5 = -10 cm :)

hope it helps ☺☺☺☺

Answer 2

Object distance u = -60 cm

Image distance v = +120 cm

Lens formula, 1/f = 1/v - 1/u

1/f = 1/120 - ( -1/60 ) = 1/120 + 1/60 = 3/120 = 40 

f = +40 cm

H(image) / H(object) = v/u

Hi = -120/60 X 5 = -10 cm

Good Luck !!!