Question

find the power of a concave lens of focal length 2m.

Answer 1

Explanation:

For concave length

Focal length is negative

Therefore

By using formula

$power \: \: p = \frac{1}{f} \\ p = \frac{1}{ - 2} \\ p = - 0.5 \: dioptre$

Answer 2

Answer:

- 0.5 Dioptres

Explanation:

Q.1) What is power of lens defined as ?

• Ans) Power of the lens is defined as the ability of the lens to converge or diverge light rays.
• It is the reciprocal of the focal length
• 1/focal length (in meters)

Q.2)What is the SI unit of the power of lens?

• Ans) The SI unit of power of lens is Dioptres. The power of lens is expressed in dioptres.

Q.3) Coming to your question, Find the power of a concave lens of focal length 2m.

Ans) In the question it is given concave lens:

In concave lens the focal length is always negative no matter where the object is placed.

So focal length = - 2m (By Sign Convention of concave lens)

Power is = 1/f(m) Formula we use here:

∴ Power = 1/- 2

= - 0.5 Dioptres