Question

A lens has a power of + 4.0 D. It is: (al A convex lens of focal length 4 m Q A convex lens of focal length 0.25 m (bX A concave lens of focal length 4 m (d) A concave lens of focal length 0.25 m​

Answer 1

Answer:

A convex lens has 4 dioptre power having a focal length 0.25 m

A dioptre, is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in meters (that is, 1/f metres). It is thus a unit of reciprocal length.

Hence, P=

0.25m

1

=4.

As the value is positive, it is a positive lens, that is, convex.