Question 405: Ray Optics

Question

A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of convex lens. The lens is placed at a distance d ahead of second wall, then required focal length will be

Accepted Answer

Using the lens formula $${1 \over f} = {1 \over v} - {1 \over u}$$
Given v = d, for equal size image |v| = |u| = d
By sign convention u = -d
$$ 	herefore $$ $${1 \over f} = {1 \over d} - {1 \over { - d}}$$
$$ \Rightarrow $$ f = $${d \over 2}$$

Answer

only $${d \over 4}$$

Answer

only $${d \over 2}$$

Answer

more than $${d \over 4}$$ but less than $${d \over 2}$$

Answer

less than $${d \over 4}$$

Ray Optics

A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of convex lens. The lens is placed at a distance d ahead of second wall, then required focal length will be

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