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Light Reflection and Refraction
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02/12/2020 12:50 pm
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How far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens? What will be the height of the image if the object is 6 cm tall?
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02/12/2020 12:56 pm
f = + 20 cm, v = +30 cm
Using, 1/f = 1/v - 1/u
we get, 1/u = 1/v - 1/f
= 1/30 - 1/20 = 2 - 3/60
= -1/60
∴ u = -60 cm
Object should be placed at a distance of 60 cm on the left side of the convex lens.
Using, m = h1/h0 = v/u
we get, Height of the image, h1 = v/u ho
= 30/(-60) x 6 = -3 cm
Negative sign shows that the image is inverted and real.