Question

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?
(ii) 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 1

Answer:

Explanation:

1. the nature of lens used for this purpose is convex lens because it produces a magnified image of the palm.

2. there are two cases for which a real and magnified img of object is obtained in convex lens-

     a. when the object is placed at focus of the lens.

     b. when the object is placed between focus and center of curvature of the          

         lens.

3. f= 10

  u = -5

 by lens formula v = -10 cm

 size of img will be enlarged

Answer 2

A convex lens is used by a palmist.

The position of the image is at -10 cm

The size of the image is twice that of the object

• 1)The lens used by palmists is convex.
• It is used by the palmist because of its ability to magnify things.
• 2) In order to magnify things the lens should be placed between F and 2F or at F. (Where F is the focus)
• 3) Given:
• Focal length of the lens (f) = +10 cm
• object distance (u) = -5 cm
• Find:
• The position and size of the image
• The size of the image
• Solution:
• I/f = (1/v) - (1/u)
• 1/10 = (1/v) - (1/-5)
• 1/v = -1/10
• ∴ v = -10 cm
• Magnification = height of image / height of object
•                          =v/u
•                          = -10/-5
•                          2
• ∴ The size of the image will be twice that of the object.
• The position of the image is at -10 cm
• The size of the image is twice that of the object