Question

focal length of a lens is -10cm then find it's power and also State it's nature​

Answer 1

Answer:

since the focal length if -ve so, it is concave in nature.

now,

f = -10cm = - 1/10 m

since p = 1/f,

=

$\frac{ - 1}{ \frac{1}{10} } \\ = \frac{ - 1 \times 10}{1} \\ = 10$

so, the power is 10 dioptre (D)

Explanation:

note" - it is necessary to convert focal length into metre.

Answer 2

Power of a lens is -2D

Negative sign indicates it is a Concave lens.

Focal length (in meters)=1/power of the lens,

Thus focal length=½=0.5m=50cm