Question

(11. Rays from the sun converges at a point 15 cm in front of a concave mirror. Where
should an object be placed so that the size of its image is equal to the size of object
12​

Answer 1

Answer:

It is given that sun rays converge at 15 cm. So, focal length of the mirror = f = 15 cm. In case of a concave mirror, the size of image and object will be same if the object is placed at 2f. Hence, in this case object must be place at 2f or 2 × 15 = 30 cm.

Answer 2

Given that, rays from the sun converges at a point 15 cm in front of a concave mirror.

We have to find that where should an object be placed so that the size of its image is equal to the size of object.

Now,

If we put the object on the centre of curvature i.e. C then the image also formed on the centre of curvature. But in downward direction.

Sun is at infinity and it's rays are falling on concave mirror, which after reflection converge at focus.

Since, object is placed 15 cm in front of a concave mirror. Means, the focal length of the concave mirror is 15 cm. But we have to find the centre of curvature.

Center of curvature is equal to twice the focal length.

→ C = 2 × f

→ C = 2 × 15

→ C = 30 cm

Therefore, object is placed at a distance of 30 cm from the concave mirror. So, that the size of its image is equal to the size of object.