the focal point of the mirror. To make it more convenient we will always take rays that come from the tip of the object. See the ray R1 in figure-8. The converse situation of previous one is also true; that is, a ray that passes through the focal point of the mirror will travel parallel to the axis after reflection.

This gives us our second ray. This will be the ray coming from the tip of the flame and going through the focal point and falling on the mirror. After reflection, this ray travels parallel to the axis. So we draw the reflected ray as a line parallel to the axis coming from the point where the incident ray meets the mirror. See R₂ in figure-9.

Using the rays R₁,R₂ and finding the point where they intersect we know the point where the image of the tip is formed

There is one more ray which is convenient to draw.

We have seen earlier that any ray that is normal to the surface, on reflection, will travel along the same path but in the opposite direction. Which ray can such a one be for a spherical mirror?

we know that a line drawn from the centre of curvature to the mirror is perpendicular to the tangent at the point where the line meets the curve. So if we draw a ray coming from the tip of the object going through the centre of curvature to meet the mirror, it will get reflected along the same line. This ray is shown as R₃ in the figure-10. In general, a ray travelling along normal retraces its path.

Along with these three rays ‘the ray which comes from the object and reaches the pole of the mirror’ is also useful in drawing ray diagrams. For this ray, the principal axis is the normal.

If we have our object (candle) placed as shown in figure-11, we can draw the ray diagram to get the point of intersection A, of any two rays coming from the top of the object and point of intersection B, of any two rays coming from the bottom of the object. We notice that point B is