Question

Power of a lens is -40, it's focal length is
O -25 m.
O -25 cm
O -2.5 m
O -2.5 cm​

Answer 1

Answer:

-2.5 cm

Explanation:

p=100/f

-40=100/f

f=100/-40

f=-2.5 cm

Answer 2

Answer:

-2.5cm is the focal length of the lens .

Explanation:

According to the Question

It is given that the power of the lens is -40 D. we have to calculate the focal length of the lens . As we know that power of the Lens is calculated by the reciprocal of its focal length. Focal length should be in metre.

• P = 1/f

where,

• P denote Power of Len
• F denote focal length

Substitute the value we get

→ -40 = 1/f

→ -40f = 1

→ f = 1/-40

→ f = -1/40

→ f = -0.025 m

Converting the unit here

→ f = -0.025 × 100cm

→ f = -2.5cm

• Hence, the required answer is -2.5cm