Question

An object is placed 100 cm in front of a diverging lens of focal length -25cm. A converging lens of focal length 33 1/3 cm is placed 30 cm past the first lens. What is the lateral magnification of this system of lenses?

Answer 1

We use 1/o + 1/i = 1/f  where o is the distance of the object, i as distance of the image and f is the focal length.
Substituting, 1/ 100 + 1 / i = - 1 /25 
i = - 20 cm 

For the case of the problem,

o = (20 + 30)  = 50 cm 

f = 33.33. Using 1 / i + 1 / o = 1/f ,  i = 100 cm 

M = magnification = - i / o 

m1 = -(-20)/100 = 20/100 = 0.2 

m2 = -100/50 = -2 

M = m1*m2 = -2 x 0.2 = -0.4.