The size of image of an object which is at infinity, as formed by a convex lens of focal length 30cm is 2 cm.If a concave lens of focal length 20cm is placed between the convex lens and the image at a distance of 26cm from the convex lens, calculate the new size of the image.

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2014-08-10T17:33:08+05:30

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h1' = - 2 cm          h = ?
f1 = + 30 cm      v1 = +30cm

f2 = -20cm        h = 2 cm
u2 = 30 - 26 = 4 cm
1/v2  = 1/f2 + 1/u2 = -1/20 + 1/4 = 1/5

v2 = 5 cm  from concave lens.
magnification = v2/u2 = 5/4 = 1.25
New image size = h" = h' * 1.25 = 2.5 cm


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