Question

give the type and power of lens having focal length -40 cm

Answer 1

the correct answer is +1.0 D

Answer 2

Given,

Focal length = -40 cm

To find,

Power and type of the lens.

Solution,

We can simply solve this mathematical problem by using the following mathematical process.

The given value of the focal length is negative, and we know that concave lenses have negative focal lengths. So, the given lens is a concave lens. (type of lens is determined)

Focal length = -40 cm = -0.4 m

Power of lens :

= 1/focal length

= 1/-0.4

= -2.5 D

(Concave lenses have negative power as well due to the negative focal length value.)

Hence, the type of lens is concave and the power of lens is -2.5D