Question

A convergent beam of light passes through a diverging lens of focal length 0.2m and comes to focus at a distance of 0.3m behind the lens. find the position of the point at which the beam would converge in the absence of the lens.?

Answer 1

Since it passes through a diverging lens, we can say that

f= -0.2m

The object is also virtual so we can say that

o= +0.3m

Lens equation:

$\frac{1}{p} -\frac{1}{o} =\frac{1}{f}$

$\frac{1}{p} -\frac{1}{0.3} =\frac{1}{0.2}$

$\frac{1}{p}=\frac{1}{0.3}-\frac{1}{0.2}$

$\frac{1}{u}= \frac{50}{6} \\u=+0.12m$

Therefore, the beam would converge at the distance of 0.12 m from the position of the lens in its absence.

Answer 2

Hope it will help you

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