A student measures the refractive index of oil. - Oil is poured into a semi-circular transparent plastic container as shown in Fig. 1.1. - The container is placed on top of a $360^\circ$ protractor as shown in Fig. 1.2. (a) The line AB shows the position of the flat side of the plastic container. A ray of light is incident at the midpoint of AB with an angle of incidence $i = 30^\circ$ as shown in Fig. 1.2. (i) State one property of the oil that is needed to ensure that the…

Physics 5054/41 — October/November 2022

Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme

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Topics Experimental Contexts · Use of Techniques, Apparatus and Materials · Analysis, Conclusions and Evaluation · Observations and Measurements · Planning Experiments and Investigations

Q113MExperimental ContextsUse of Techniques, Apparatus and MaterialsObservations and MeasurementsAnalysis, Conclusions and EvaluationFree sample

A student measures the refractive index of oil.

Oil is poured into a semi-circular transparent plastic container as shown in Fig. 1.1.
The container is placed on top of a $360^\circ$ protractor as shown in Fig. 1.2.

Fig. 1.1

Fig. 1.2

(a)

The line AB shows the position of the flat side of the plastic container.

A ray of light is incident at the midpoint of AB with an angle of incidence $i = 30^\circ$ as shown in Fig. 1.2.

(i)

State one property of the oil that is needed to ensure that the experiment works.

______

(ii)

On Fig. 1.2, measure the angle of refraction $r$ of the light in the oil.

$r$ = ______ $^\circ$

(b)

The student repeats the procedure described in (a) and measures the angle of refraction $r$ for angles of incidence $i = 15^\circ$ , $45^\circ$ , $60^\circ$ , and $75^\circ$ . The results are shown in Table 1.1.

Table 1.1

$i / ^\circ$	15	30	45	60	75
$r / ^\circ$	11		31	39	45

(i)

Complete Table 1.1 with your value of $r$ from (a)(ii).

On the grid provided in Fig. 1.3, plot a graph of $r$ on the y-axis against $i$ on the x-axis. Start your axes from (0,0). Draw a smooth curve of best fit.

Fig. 1.3

(ii)

Describe the relationship between $i$ and $r$ shown by the graph.

(iii)

Use your graph to find the value of $r$ when $i = 50^\circ$ .

Show on the graph how you determine your answer.

$r$ = ______ $^\circ$

(iv)

Theory suggests that the refractive index $n$ of the oil is given by:

n = \frac{\sin i}{\sin r}

Using $i$ and your value of $r$ from (b)(iii), calculate a value for $n$ . Give your answer to an appropriate number of significant figures.

$n$ = ______

(v)

On Fig. 1.4, sketch the graph when $\sin r$ is plotted against $\sin i$ . No calculations are required.

Fig. 1.4

(c)

Suggest one reason why the practical method used in this investigation might not give an accurate value for $n$ .

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