Question

A convex lens forms a real and inverted image at a distance of 50cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? (a) 0.25m (b) 0.30m (c) 0.35m (d) 0.40m​

Answer 1

It is given that the image is formed at a distance of 50cm from the lens. And since the image is real, v = +50cm. This means that u = -50cm. Therefore, the needle must be placed at a distance of 50cm from the lens.

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Answer 2

Question :-

A convex lens forms a real and inverted image at a distance of 50cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object?

(a) 0.25m (b) 0.30m (c) 0.35m (d) 0.40m

Answer :-

• (a) 0.25m

Step by step explanation :-

It is given that the image is formed at a distance of 50cm from the lens. And since the image is real, v = +50cm.

This means that u = -50cm.

Therefore, the needle must be placed at a distance of 50cm from the lens.

Substitute the values of v and u in formula.

Formula,

$\rm:\longmapsto{\frac{1}{v} - \frac{1}{u} = \frac{1}{f} }$

$\rm:\implies{ \frac{1}{50} - \frac{1}{ - 50} = \frac{1}{f} } \: \: \: \: \: \: \: \: \: \\ \\ \rm:\implies{ \frac{1}{f} = \frac{2}{50} = \frac{1}{25} } \: \: \: \: \: \: \: \: \: \: \: \: \\ \\ \bf:\implies \red{f = 25cm = 0.25m}$

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a convex lens forms a image of needle at distance of 25cm from it where is the needle placed of the image is equal to the size of the object.

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