A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power - 2.5 D. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of 10 cm from the lens ?

A person suffering from myopia (near-sightedness) was advised to wear

1.	A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power - 2.5 D. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of 10 cm from the lens ?
Answer» Solution :Power of lens P = - 2.5 `therefore`Focal length of lens f = `(1)/(p)=(1)/(2.5)= - 0.40 m = - 40 cm` Let the object be PLACED at a distance u in FRONT of the given lens so that its image is formed at a distance v = 10 cm from the lens. Since the lens is a diverging (concave) lens, as per signconvention, u, v as well as f have -ve sign. HENCE, as per lens formula `(1)/(v)-(1)/(u)=(1)/(f )` we have `RARR u=-40/3 cm =-13.3 cm ` So object should be placed at a distance of 13.3 cm from the lens.