Question

2.Two lenses of powers -4D and +5D are kept in contact. What is the focal length of the combination? What is the nature of the combination?

Answer 1

There are 2 lenses of power -4D and +5D

Power of lens combination = 5D - 4D

= 1D

Focal length is the reciprocal of power.

Therefore Focal length = 1/1 = 1m

The focal length of the lens = 1m

Since the power and focal length of lens is positive, the nature of lens is Convex lens.

Additional information:

• Focal length and power of Concave lens is negative.
• Focal length is the ability of lens to coverage or diverge light rays falling on it.
• When 2 or more lenses are placed in contact, the powers are just added