You place an object 40 cm in front of a concave spherical mirror of focal length

Question

You place an object 40 cm in front of a concave spherical mirror of focal length 30 cm. At what distance in front of the mirror is the image formed? 30 cm 120 an 17 cm 90 cm 40 cm Ray tracing is a simple way to understand how a lens forms an image of an object. Fig. 3 in the lab description and Fig. 33-6 in the textbook show examples of ray tracing for converging lenses. Ray tracing is also helpful in understanding combinations of lenses (see Fig. 33-14 in the textbook). The figure shows a combination of two converging lenses and a light ray (Ray A2) that emanates from the object (OA), passes through the focal point in front of the lens, and leaves the lens parallel to the optical axis (compare with Ray 2 in Fig. 3 (b)). What will happen to the ray as it passes through the second lens, LB? It will remain parallel to the optical axis. It will be refracted away from the optical axis, as if it had passed through the focal point F?B. It will be refracted toward the optical axis and pass through the focal point FB on the other side of the lens. It will be refracted toward the optical axis but will not necessarily pass through the focal point FB on the other side of the lens.

Explanation / Answer

f= -30 cm
s = -40 cm
use:
1/f = 1/s' + 1/s
1/(-30) = 1/s'+ 1/(-40)
1/s' = 1/40 - 1/30
s'= - 120 cm
Negative sign shows that image is on the same saide of object
Answer : 120 cm

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For 2nd lens the ray is parallel to the lens. So after refraction it will pass through focus FB
Answer: option 3

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