State one property of the oil that is necessary for the experiment to work.
On Fig. 1.2, measure the angle of refraction $r$ for the light travelling in the oil. $r = \ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots^{\circ}$
Complete Table 1.1 with your value of $r$ from (a)(ii). On the grid in Fig. 1.3, plot $r$ on the y-axis against $i$ on the x-axis. Begin both axes at $(0,0)$. Draw a smooth best-fit curve.
Describe the way $i$ and $r$ are related on the graph.
Use your graph to find the value of $r$ for $i = 50^{\circ}$. Show clearly on the graph how you obtained your answer. $r = \ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots^{\circ}$
Theory gives the refractive index $n$ of the oil as: $n = \frac{\sin i}{\sin r}$ Substitute $i$ and your value of $r$ from (b)(iii) to calculate $n$. State your answer to an appropriate number of significant figures. $n = \ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots$
On Fig. 1.4, sketch the graph obtained when $\sin r$ is plotted against $\sin i$. No calculations are needed.
Suggest one reason why the practical method in this investigation may fail to produce an accurate value for $n$.