Calculate the distance at which an object should be placed infront of a concave lens of focal length 30 cm to obtain an image of half of its size.
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Calculate the distance at which an object should be placed infront of a concave lens of focal length 30 cm to obtain an image of half of its size.f1 = 25 cm = 0.25 m
p1 = 1/f1 = 1/0.25 = 4D
f2 = -10 cm = -0.1m
p2 = 1/f2 = 1/-0.1 = -10D
(a) Power of the combination:
P = p1 + p2
= 4D + (-10D)
= - 6 D
(b) Focal length of the combination:
f = 1/P = 1/-6 = -0.1666m = -16.66cm
(c) The combination has negative focal length, so it is diverging.
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