Question

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

Answer 1

Given :-

• Image formed is real and inverted.
• Image distance (v) = 50 cm

To find :-

• Object i.e. needle distance from the lens
• Power of lens.

Solution :-

i) Let the object distance be u.

Magnification in a lens (m) = v/u

-1 = 50/u

u = -50 cm

● The needle is placed 50 cm in front of the convex lens.

ii) Power of the lens p = 1/f

P = 1/25cm^ -1

P = 1/25 × 10-2 m^ -1

P = 4m^ -1

Since 1m-1 = 1D

P = 4D

● Power of lens is 4D.

Hope it helps !

Answer 2

Answer:

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