Question

A 2 cm tall object is placed 20 cm to the left of a converging lens. The focal length of this lens is 10 cm. Another converging lens of focal length 15 cm is place 10 cm to the right of the lens. What is the tall of the final image 0.6 cm 0.8 cm 1.5 cm 2 cm 3 cm

Answer 1

for the converging lens :
di = (do * f)/(do - f)
= (20 * 10)/(20 - 10) = 20 cm

for the converging lens :
do = 20 + 10 = 30 cm
di = (do * f)/(do - f)
= ( 30* (15))/(30 - 15)
= 30 cm --> it's the position of the final image)

the height of the final image:
h''/h = l di/dol * ldi'/do'l
h''/2 = (20/10) * (30/30)
h'' = 2.0 cm