Describe the steps the student should take to draw: (i) a normal line $NL$ perpendicular to the side $PQ$ at a distance of $3.0cm$ from corner $P$, extending through to side $RS$. (ii) an incident ray line $A{S}^{\prime }$ at an angle of incidence $i=40^{\circ }$ to the normal, above side $PQ$ and to the left of the normal, where $S^{\prime }$ is the intersection of the normal with $PQ$.

To trace the ray, the student places two pins, $P_1$ and $P_2$, on the line $A{S}^{\prime }$. (i) Tick the correct statement about the separation of pins $P_1$ and $P_2$ to produce the most accurate ray-trace:

• exactly $2.0cm$ apart
• less than $4.0cm$ apart
• more than $5.0cm$ apart

(ii) Explain the physical reason for placement at this separation.

Suggest two practical techniques, other than pin separation distance, that the student should use to ensure that the ray-trace is as accurate as possible.

The student plans to investigate how the angle of refraction varies with the angle of incidence. State four suitable values of the angle of incidence $i$ that the student could use to carry out this investigation.