Ask a Teacher

Image produced by convex mirror is small.why

In the above figure, we have an object AB placed in front of a convex mirror M anywhere between pole P and infinity. A ray of light AD, parallel to the principal axis of the convex mirror, strikes the mirror at point D. Now, according to the first rule of image formation, this parallel ray of light should appear to be coming from focus after reflection. So we join the points D and F by a dotted line and produce the line FD towards the left in the direction DX. Now, DX gives us the reflected ray which appears to be coming from focus F of the convex mirror.

We have now to draw a second ray of light from the point A going towards the centre of curvature C of the convex mirror. For this we join the point A with point C by a line which cuts the mirror at point E. The line from A to E is a solid line and it represents a real ray of light but the line from E to C is a dotted line which represents a virtual ray of light. Now, AE represents a ray of light   going towards the centre of curvature C of the convex mirror. According to the second rule of image formation, this ray is reflected along the same path EA but it appears to be coming from the centre of curvature C.

The two reflected rays DX and EA are diverging rays but they appear to intersect at point A' when produced backwards. Thus A'  is the virtual image of point A of the object. To get the full image of the object, we draw the perpendicular A^'B^'  to the axis from point A^I .Thus A^'B'  is the virtual image of the object AB. It is clear from the above figure that the image is formed behind the convex mirror between the pole and the focus. It is virtual, erect and smaller than the object (or diminished). From the above discussion we conclude that :When an object is placed anywhere between pole (P) and infinity in front of a convex mirror, the image formed is :

(i)behind the mirror between pole (P) and focus (F)’

(ii)Virtual and erect, and

(iii)diminished (smaller than the object)