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Light Reflection and Refraction
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02/12/2020 11:02 am
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A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it forms a real and inverted image 20 cm away from the lens? What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case.
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02/12/2020 11:08 am
f = +10 cm, v = +20cm as image is real and inverted. Height of the object = 2 cm. (say + ve)
Using, 1/f = 1/v - 1/u, we get
1/u = 1/v - 1/f
= 1/+20 - 1/10
= +1 - 2/20 = - 1/20
∴ u = -20 cm = 2f
Object is placed at 2F, image is also formed at 2F on the other side of the lens. So, image will be of the same size as the object as |u| = |v| and, therefore, the height of the image will be 2 cm.