Question

A concave mirror of radius of curvature 40 cm is to be used to obtain a real image of an object. The image is to be one-third as large as the object. Where should the object be placed and where is the image found

Answer 1

if r = 40 cm , then f = r/2 = 40/2 = 20 cm

then for a real image by a concave mirror,

magnification M = f/u-f => 2 = 20/U-20

therefore 2(u-20) = 20

2u - 40 = 20

2u = 40 + 20

2u = 60/2 = 30 cm

Hope this helps you.....

Answer 2

Answer:

The object be placed and where is the image found is round 30 cm.

Explanation:

• A concave mirror is a called as spherical mirror.
• When a sphere which is hollow it will be cut into different parts and outer surface is also part that is cut and painted that will become a mirror.
• Here, the mirror will have an inner surface which is reflecting. This mirror is known as a concave mirror.
• The image that has formed in the concave mirror is very small or can be large and virtual in nature.
• The concave mirror is placed to be very close to a object and a magnified, erect and virtual image is seen to be obtained.

Given that:

Radius of curvature = 40 cm

Image of object = 1/3 rd large

To find:

The object that is placed and where the image will be found =?

Solution:

Let the radius r = 40cm

Then using,

f = r/2

f = 40/2

f = 20 cm

Now, the real image of the concave mirror will be

By using the formula:

Magnification M = f/u-f

                    Here, m =2

                             f= 20

2 = 20/u -20

2(u-20) =20

2u- 40 =20

2u =40+20

2u = 60/2

Therefore,

u = 30 cm

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