Question

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

Answer 1

Answer:

Given,

Focal length, f=50cm

Power, P=

f

100

=

50

100

P=2D

Since, focal length in +ve lens is convex.

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Answer 2

Given,

Focal length of the lens = -40 cm

To find,

The power and type of the lens.

Solution,

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

Focal length of the lens = -40 cm = -0.4 m

Now,

Power of the lens = 1/focal length

Power of the lens = 1/(-0.4) = -2.5 D

And,

The power and the focal length of the given lens are negative. Only concave lens (diverging lens) have negative focal length and negative power. So, the said lens is absolutely a concave lens (or, diverging lens).

Hence, the power of the lens is -2.5D and the lens is a concave lens (or, diverging lens).