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Light Reflection and Refraction
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03/12/2020 12:11 pm
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A 6 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 15 cm. The distance of the object from the lens is 10 cm. Find the position, size and nature of the image formed, using the lens formula.
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03/12/2020 12:18 pm
For convex lens
f = +15 cm, u = - 10 cm
Using lens formula
1/f = 1/v - 1/u
1/15 = 1/v - 1/-10 = 1/v + 1/10
∴ 1/v = 1/15 - 1/10 = 2 -3/30 = - 1/30
v = -30 cm
Thus, the image is formed on the same side of the object at a distance of 30 cm from the optical centre of the lens.
Negative sign indicates that image is virtual.
Now h1 = 6 cm
So, using,
m = h2/h1 = v/u
h2 = v/u x h1 = -30/-10 x 6
= 18 cm
So, image is three times larger than the size of object, i.e. 18 cm.
The positive sign indicates that the image is erect.