The student draws an incident ray line and places two pins, $P_1$ and $P_2$, along it. State the minimum recommended distance between $P_1$ and $P_2$ and explain why this distance is necessary for an accurate ray-trace.

The student sets the angle of incidence to $i=55^{\circ }$. (i) Calculate the expected angle, $\theta$, between the incident ray and the reflecting surface of the mirror. (ii) State the expected angle of reflection, $r$.

Suggest two practical precautions that the student should take when performing this ray-trace experiment to ensure the accuracy of their drawings and alignments.

Suggest one practical reason why the measured angle of reflection might not perfectly match the theoretical prediction from the law of reflection, even when the experiment is performed carefully.