Question

Define principal focus of concave lens
and convex lens
Also draw ray diagrams in each case? ​

Answer 1

Explanation:

Principal Focus

When parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.

Light ray diagram of an image formed, when the object is placed in between principal focus FF and 2F2F is given in the above figure.

Lens Formula is given by:-

f

1

=

v

1

−

u

1

where,

f = focal length of the lens.

v = distance of image from the optic center of the lense.

u = distance of object form the optic center of the lens.

The power of any lens is given by the formula:-

Power=

Focal length of the lens

1

(in diopter)

therefore, Power=

0.5

1

=2 diopter

Fand 2F is shown in the diagram above.

Answer 2

Answer:

The principal focus of a convex lens is defined as the point on which the principal axis of the light is parallel to the principal axis that converges after the refraction from the lens. The principal focus of concave lens is when the light rays get diverged and appear to form a single point.