Given a two lens system, a converging lens with a focal length f1 = 10.0 cm, and

Question

Given a two lens system, a converging lens with a focal length f1 = 10.0 cm, and a diverging lens a distance d from the converging lens having a focal length f2 = -15 cm. Path of light travel is incoming parallel to the converging lens, then towards and through the diverging lens. Assume f1 + f2 < d < f1 , such that the system acts as a converging lens with effective focal length f_eff.

Q:

1) Find the image distance i1 for the initially parallel rays that pass through the diverging lens.

* For this I got 1/f2 = 1/p2 + 1/i2 where p is object distance, and i is image distance. P goes to infinity because of parallel lines, then i2 = f2 = -15.00 cm. <I think>

2) Use your answer from part 1) to find p2, the object distance for the diverging lens. Hint: The image of the first lens is the object for the second lens, and a virtual object has a neg. object distance.

Explanation / Answer

Solution:

The image distance for the converging lens = i1 = focal length of the converging lens since the rays are coming parallel to the principal axis = 10 cm.

The focal length of the diverging lens = -15 cm

object distance for the diverging lens = - 5cm

Image distance for the diverging lens:

1/i2 = 1/-15-(-1/5) =0.1333

=>i2 =1/0.133 = 7.5 cm

The positive values shows that the final image is real.

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