What is the nature of a lens whose power of `-4 D` ?

Define power of a lens. What is its unit ? One student uses a lens of focal length 50 cm and another of - 50 cm . What is the nature of the lens and power used by each of the them ?

Find the focal length and nature of a lens whose optical power is -5D.

What will be the focal length of a lens whose power is given as + 2.0 D ?

Define power of a lens. What is its unit ? One student uses a lens of focal length 50 cm and another of - 50 cm . What is the nature of the lens and its and power used by each of the them ?

What is the meant by power of a lens? How the power of a lens related with focal length?

The power of a lens is -5D. What is the nature of the lens and what is the focal length?

What is focal length of a lens of power 2.5 D ?

A lens is a focal length - 0.5 m. What is the nature and power of the lens?

What do you mean by power of a lens ? What is the SI unit of the power of a lens ? Calculate the power of a concave lens of focal length 25 cm.