a small object is 25.0 cm from a diverging lens as shown in the figure(figure 1)

Question

a small object is 25.0 cm from a diverging lens as shown in the figure(figure 1). a converging lens with a focal length of 12.4cm is 30.0 cm to the right of the diverging lens. the two-lens system forms a real inverted image 17.0 cm to the right of the converging lens.

What is the focal length of the diverging lense?

a small object is 25.0 cm from a diverging lens as shown in the figure(figure 1). a converging lens with a focal length of 12.4cm is 30.0 cm to the right of the diverging lens. the two-lens system forms a real inverted image 17.0 cm to the right of the converging lens. What is the focal length of the diverging lense?

Explanation / Answer

We use,

1/do2 + 1/di2 = 1/f2

with di2 = 17 cm and f2 = 12.4 cm
1/do2 + 1/17 = 1/12.4

1/do2 + 0.059 = 0.081
1/do2 = 0.022
do2 = 45.45 cm

This means di1 = 30 - 45.45 = -15.45 cm (15.45 cm to the left of the diverging lens).

So for the diverging lens

1/do1 + 1/di1 = 1/f1

1/25 + 1/(-15.45) = 1/f1
0.04 - 0.065 = 1/f1
f1 = 40 cm

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