Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose. (i) State the nature of the lens and reason for its use. (ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object? (iiii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.

Rishi went to a palmist to show his palm. The palmist used a special l

1.	Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose. (i) State the nature of the lens and reason for its use. (ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object? (iiii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.
Answer» Solution :(i) The LENS is a convex lens of small focal length. Its use enables the palmist to see lines on the palm of Rishi in details because the lens forms magnified image. (ii) Palmist should hold the lens at a distance slightly greater than its focal length f (INFACT between f and 2f) so as to have a real and magnified image of the object. (iii) Here f = +10 cm and u = -5CM As PER lens formula `(1)/(v)-(1)/(u)=(1)/(f)`, we have `(1)/(v)=(1)/(f)+(1)/(u)=(1)/(10)+(1)/((-5))=(1-2)/(10)=-(1)/(10) RARR v=-10cm` and `m=(v)/(u)=((-10))/((-5))=+2` Thus, a virtual and erect image is formed at a distance of 10 cm from the lens and image is an enlarged image whose size is two times that of the object (i.e., palm).