Q26. The best way to "see" what is going on is to make several ray diagrams with the object closer and closer to the thin converging lens. When the object is far away, the real image is small, inverted, and is just beyond the focal point. As the object approaches the focal point, the image gets larger, remains inverted, and moves farther away from the lens. When the object reaches the focal point, the two rays you can still draw come away from the lens parallel to each other so they don't cross until they are infinitely far away. When the object is closer than the focal point, the image becomes virtual.
Q34. LENS: Light is refracted at the front and rear surfaces of the
lens to form the image and this refraction is described by Snell's Law. When the
index of refraction of the medium around the lens changes, the angle of refraction of the
incoming light as it enters the lens changes.
n(outside lens) x sin(angle
of incidence outside lens) = n(inside lens) x sin(angle of refraction inside lens)
If there is a change in how much light rays are bent on entering the lens, there will be a
change in the focal length of the lens. This will lead to a change in the image
distance.
MIRROR: When light is reflected from a mirror, the angle of incidence equals
the angle of reflection no matter what the index of refraction of the medium is in front
of the mirror. This means both the focal length and the location of the image
are the same for any transparent medium in front of the lens.
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