On Fig. 3.1, draw a normal NL to side AB of the transparent block at a point 2.0 cm from A. Extend the normal so that it passes through side CD of the block. Mark the point S where NL crosses AB.
Draw a line RS at an angle $i = 30\degree$ to the normal, above AB and to the left of the normal. The student places two pins P1 and P2 on line RS. Mark, with two crosses (X), on line RS, positions of the pins at a suitable distance apart for this experiment.
Draw a line through the positions of P3 and P4. Extend the line until it meets the normal NL and label that point E. Mark the other end of the line F. Measure the acute angle $\theta$ between EF and the normal. An acute angle is an angle less than $90\degree$.
Tick one box to finish the statement. For the most accurate ray-trace, a student places pins P1 and P2 exactly 5.0 cm apart; less than 5.0 cm apart; more than 5.0 cm apart.
Suggest two further techniques that the student could use to produce an accurate ray-trace.
List values of angle i that are suitable for the student to use.