An object is kept $60$ $c m$ from a lens gives a virtual image $20$ $c m$ in front of lens. What is the focal length of the lens? Is it converging lens or diverging lens?

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Solution

From lens formula, $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

$= \frac{1}{(- 20)} - \frac{1}{(- 60)} = - \frac{2}{60}$

$\Rightarrow f = - 30 c m$

Since the focal length is negative. It is a diverging lens.

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An object is kept 60 cm from a lens gives a virtual image 20 cm in front of lens. What is the focal length of the lens? Is it converging lens or diverging lens?

From lens formula, 1f=1v−1u =1(−20)−1(−60)=−260 ⇒f=−30cmSince the focal length is negative. It is a diverging lens.

An object is kept $60$ $c m$ from a lens gives a virtual image $20$ $c m$ in front of lens. What is the focal length of the lens? Is it converging lens or diverging lens?

From lens formula, $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

$= \frac{1}{(- 20)} - \frac{1}{(- 60)} = - \frac{2}{60}$

$\Rightarrow f = - 30 c m$

Since the focal length is negative. It is a diverging lens.