Question

When a concave mirror is held towards the sun and its sharp image is formed on a piece of carbon paper for some time, a hole is burnt in the carbon paper. What is the name given to the distance between the mirror and carbon paper? (a) Radius of curvature

(b) Focal length

(c) Principal focus

(d) Principal axis​

Answer 1

Answer:

The nature of the spherical mirror is a concave mirror. (b) The hole is burnt in the carbon paper because most of the sun's heat rays are focussed on the sun's image point and this can burn the carbon paper's hole. (c) The carbon paper is placed at the focus of the spherical mirror.

Answer 2

The name given to the distance between the mirror and carbon paper is (b) Focal length.

Explanation:

• A concave mirror is a type of spherical mirror in which the reflecting surface is the inner curved surface of the sphere.

• Formation of image depends on the distance between the object and the mirror. Concave mirrors form both real and virtual images.

• When the concave mirror is placed very close to the object, a virtual and magnified image is obtained and if we increase the distance between the object and the mirror, the size of the image reduces and real images are formed.

Here, the object is sun which is at infinity.

Rays from infinity, intersect a the principal focus of the mirror.

So, the image is formed at focus, carbon paper acts as a screen and the name of the distance between mirror and carbon paper is focal length.

The characteristic of image formed here are:

1. Real i.e. infront of mirror.
2. Inverted and diminished.