figure-4). Now we shall develop a technique to draw ray diagrams when an object is placed anywhere on the axis of the mirror and validate the above observations.

Here we will take at least two rays originating from the same point on the object but with different direction, see how they get reflected from the mirror and find out the point where they meet to form the image.

Let us take an example

As shown in the figure-7, assume a concave mirror and a candle placed at some distance along the axis of the mirror.

The diagram shows two rays coming from the tip of the flame (object). The reflected rays are constructed based on the laws of reflection.They meet at point A. The tip of the flame of the reflected image will be at the point of intersection, A.

• Why only at point A?

If we hold the screen at any point before or beyond point A (for example at point B), we see that the rays will meet the screen at different points. Therefore, the image of the tip of the flame will be formed at different points due to these rays. If we draw more rays emanating from the same tip we will see that at point A they will meet but at point B they won’t. So, the image of the tip of the flame will be sharp if we hold the screen at point A and will become blurred (due to overlaping of multiple images) when we move the paper slightly in any direction (forward or backward). Is this not something that you observed during the previous experiment with sun rays?

However, it is not going to be easy to evaluate the angle of reflection for any arbitrary ray, every time we will have to find the normal, measure the incident angle and construct a ray with equal angle on the other side. This would be a tedious task, can we find any other simpler method?

Yes, there are a few. Based on our discussion so far, we can identify some appropriate rays which we can take as representative rays to find the point ‘A’.

We have seen that all rays that are parallel to the axis get reflected such that they pass through the focal point of the mirror. So, for drawing any diagram the most suitable ray to draw will be the one that comes from the object and goes parallel to the axis of the mirror. The reflected ray will be the line drawn from the point of incidence on the mirror and passes through