Question

An object of height 6cm is placed at a distance of 20cm in front of a concave lens of power -8D. Find the size of the image?

Answer 1

Explanation:

i hope this is helpful for you

Answer 2

The size of the image is 2.28 cm.

Given,

The height of an object is 6 cm. It's the distance from the concave lens is 20 cm. The power of the lens is -8D.

To find,

The size of the image.

Solution,

Let the image distance from the lens be v cm.

The size of the object is(h)=6cm.

Object distance(u)=-20cm.

We know that the power is the reciprocal of the focal length(metres).

P=1/f

From here, the focal length is -1/8m

To find the image distance in the given question we will use the lens formula.

1/f=1/v-1/u.

1/f=1/v-1/u

-8/100=1/v+1/20

1/v=-2/25-1/20

1/v=-[2/25+1/20]

1/v=-[13/100]

v=-100/13.

v=-7.6 cm.

We have image distance, object distance as well as height of the object. To find the height of the image we can use the magnification which can be found by both image and the object distance and the heights of the object and the image.

Magnification= -v/u=h'/h

-(-7.6)/-20=h'/6

h'=-[7.6×6/20]

h'=2.28cm.

So, the height of the image is 2.28cm.

#SPJ3