Question

A) Two lenses have power of i) +2D ii) -4D. What is the nature and focal length of each
lens?
B)An object is kept at a distance of 100cm from each of the above lenses. Calculate:
i) Image distance
ii)Magnification
in each of the two cases

Answer 1

1)the power of a lens is 2.5D.what is the focal length and type of lens.

2)the focal length of a concave mirror is 30cm.Find the position of the object in front of mirror so that the image is 3times the size of the object

3)an object is placed in front of a convex mirror of radius of curvature 60cm.Find the position of image and its magnification

Answer 2

Resultant Power of a lens is equal to the sum of the powers of the individual lenses.

Resultant power = + 2 dioptre + (-4 dioptre) = -2 dioptre

 

As the sign of the resultant power of the lens is negative it is a concave lens