SNC 2D
11.9 Reflection in a Circular Convex Mirror
REQUIRED APPARATUS:
Ray Box with single-slit and triple-slit windows
circular convex mirror.
Ruler
Blank pieces of paper.
Part A: Locating C and F
1. Set the mirror flat on a piece of paper and draw
its convex side.
2. Aim a single light ray toward the center of the
mirror so it reflects onto itself.
3. Mark the ray with a few dots.
Remove the mirror and draw that ray.
4. Now move the ray box around and find a second ray that reflects onto itself.
Mark it and draw it.
5. Repeat this for a third ray, as shown in Figure 22-19(a).
6. This time, extend the rays behind the mirror and mark the point where the virtual rays meet
as C (centre of curvature).
7. Measure the radius of curvature, r, and mark this on your diagram.
8. Set the triple-slit window into the ray box, and check to be sure the emerging rays are
parallel.
9. Draw the convex shape of the mirror on a new diagram.
10. Aim three parallel rays of light toward the mirror so that the middle ray strikes the mirror and
reflects back on itself. The other rays should spread out. See Figure 22-19(b).
11. Draw all incident and reflected rays.
12. Again, extend the reflected rays behind the mirror and find the point where the reflected rays
meet. This is F (the focal point).
Label it and measure the focal length, f, and write it on the diagram.
SNC 2D
Part B: Learning the Rules for Ray Diagrams
1. Starting a new diagram, aim a single ray toward the
middle of the mirror
so it strikes it and reflects onto itself.
2. Mark and draw this ray label it as the P.A (principal
axis).
3. Use the measurements found in Part A to measure and
label points C and F.
4. Use a single ray and a convex mirror to determine each
of three important rules for convex-mirror reflection as
stated in the observations.
Draw all three rays on your diagram. (See Figure 22-20.)
(a) An incident ray parallel to the principal axis will reflect
back and appear to come from ___________.
(b) An incident ray that is aimed to go through F will reflect
back and come out _____________ to the P.A.
(c) An incident ray that is aimed to go through C will reflect back _____________________.
CONCLUSIONS
1. What extra step must be taken to locate C and F for a convex mirror compared to a concave
mirror?
2. Is the distance to C the still twice the distance to F for a convex mirror?
Support your answer with the numbers from your experiment.
3. The word diverge means to spread apart. Explain why a convex mirror may be called a
diverging mirror