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 ? Alsi, find the power of the lens.

A convex lens forms a real and inverted image of a needle at a distanc

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 ? Alsi, find the power of the lens.
Answer» <P> Solution :Since the image is real and same size. The position of image should be at 2f. It is given that the image of the needle is formed at a distance of 50 cm from the convex LENS. Hence, the needle is PLACED in front of the lens at a distance of 50 cm. Object distance, `u = -50 cm` Image distance, v = 50 cm Focal LENGTH = f According the lens formula, `(1)/(v)-(1)/(u)=(1)/(f)` `(1)/(f)=(1)/(50)-(1)/((-50))=(1)/(50)+(1)/((50))=(1)/(25)` f = 25 cm = 0.25 cm Power of lens, `p=(1)/("f (in METERS)")=(1)/(0.25)=+4D`