# GCSE Physics Revision: Properties of waves, including light and sound Alternative to Practical

Figure shows a ray tracing sheet obtained by a student carrying out a reflection of light experiment using pins and a plane mirror. The student looks into the mirror MM’ and views the images of pins A and B. He then places pins C and D so that pins C and D and the images of pins A and B appear to be in line.
(a) On the figure,
(i) draw the incident ray in this experiment,
(ii) draw the reflected ray,
(iii) draw a normal at the point where the incident ray meets the mirror,
(iv) measure the angle of incidence i.

(b) The student moves pin B and then repeats the experiment, obtaining the reflected ray EF.
(i) On the figure, continue the lines CD and EF behind the mirror to find the point where they meet. Label this point X.
(ii) Draw the line AX. Label with the letter Y the point where line AX crosses the mirror MM’.
(iii) Use your rule to measure the distances AY and YX.

(c) According to theory, AY = YX. Suggest why, in spite of very careful work, the student’s values may have been slightly different.