# To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions after reflection from the mirror

To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions after reflection from the mirror. Choose these two rays and state the path of these rays after reflection from a concave mirror. Use these two rays to find the nature and position of the image of an object placed at a distance of 15 cm from a concave mirror of focal length 10 cm.

Answer:
The candidate may choose the following rays:

1. A ray parallel to the principal axis, after reflection, will pass through the principal focus of a concave mirror.
2. A ray passing through the centre of curvature of a concave mirror after reflection is reflected back along the same path.
Object distance, u = - 15 cm, focal length,f= - 10 cm, image distance, v = ?
Apply mirror formula,

The image is formed at a distance of 30 cm in front of the mirror (negative sign means object and image are on the same side). It is real and inverted.