Question

Define lens formula and magnification of lens.

Answer 1

1v + 1u = 1f

v= distance of image from the lens

u= distance of object from the lens

f= focal length of the lens

The lens formula is applicable to all situations with appropriate sign conventions.

 

Calculating magnification with the help of lens formula:

Magnification of a lens is defined as the ratio of the height of image to the height of object. It is also given in terms of image distance and object distance. It is equal to the ratio of image distance to that of  object distance.

m=hiho=vu

Where, m= magnification

hi = height of image

ho= height of object

 

Power of lens: Power of a lens is the measure of degree of convergence or divergence of the light rays falling on it. The degree of convergence or divergence depends upon the focal length of the lens. Thus we define power of lens as the reciprocal of the focal length of the lens used. It is given as,

Where f is the focal length of the lens used. SI unit of power is Dioptre (D). The power of concave lens is negative while the power of convex lens can be positive.