Question

Power of a lens is + 5 diopters .
What is the nature and focal length of this lens?
At what distance from the lens should an object be placed so as to get its inverted image of the same size?

Answer 1

Since Power is + ve the lens is *Convex*

f = 1/P

= 1/5

= +0.2 m

In a convex lens an object placed at 2f produces an inverted image of same size

Therefore, required position = 2*f

= 2*0.2

= 0.4m

Answer 2

Answer:

The focal length will be 20 cm and this lens is convex lens. The image is formed at the curvature at 40 cm.

Explanation:

Given that,

Power P = +5

We know that,

The power of the lens is the reciprocal of the focal length of the lens.

$P=\dfrac{1}{f}$

The focal length of the lens is

$f = \dfrac{1}{P}$

$f= \dfrac{100}{5}$

$f = 20\ cm$

This lens is convex lens.

We know that,

When the object placed at the curvature then the image is formed inverted and same size of the object and curvature will be 2 F.

Therefore, Curvature will be

$C= 2\times20\ cm$

$C= 40\ cm$

Hence, The focal length will be 20 cm and this lens is convex lens. The image is formed at the curvature at 40 cm.