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A converging beam of light is incident o...

A converging beam of light is incident on a concave lens of focal length 20 cm. In the absence of the lens, the beam converges at a point 10 m behind the lens. Find where the beam will converge/diverge after refraction.

Text Solution

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The situation is shown. O is the virtual object
u = + 10 cm
f = -20 cm
`(1)/(v) - (1)/(u) = (1)/(f)`
`(1)/(v) = (1)/(u) + (1)/(f) = (1)/(10) - (1)/(20) = (1)/(20)`
`rArr v = + 20 cm`. The beam converges at a point 20 cm behind the lens.
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