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Date November 2016 Marks available 5 Reference code 16N.3.SL.TZ0.1
Level Standard level Paper Paper 3 Time zone 0 - no time zone
Command term Determine, Draw, and Outline Question number 1 Adapted from N/A

Question

A student measures the refractive index of water by shining a light ray into a transparent container.

IO shows the direction of the normal at the point where the light is incident on the container. IX shows the direction of the light ray when the container is empty. IY shows the direction of the deviated light ray when the container is filled with water.

The angle of incidence θ is varied and the student determines the position of O, X and Y for each angle of incidence.

The table shows the data collected by the student. The uncertainty in each measurement of length is ±0.1 cm.

(i) Outline why OY has a greater percentage uncertainty than OX for each pair of data points.

(ii) The refractive index of the water is given by O X O Y when OX is small.

Calculate the fractional uncertainty in the value of the refractive index of water for OX = 1.8 cm.

[3]
a.

A graph of the variation of OY with OX is plotted.

(i) Draw, on the graph, the error bars for OY when OX = 1.8 cm and when OY = 5.8 cm.

(ii) Determine, using the graph, the refractive index of the water in the container for values of OX less than 6.0 cm.

(iii) The refractive index for a material is also given by sin i sin r where i is the angle of incidence and r is the angle of refraction.

Outline why the graph deviates from a straight line for large values of OX.

[5]
b.

Markscheme

i
OY always smaller than OX AND uncertainties are the same/0.1
« so fraction  0.1 O Y > 0.1 O X »

ii
0.1 1.3 AND 0.1 1.8
= 0.13 OR 13%

Watch for correct answer even if calculation continues to the absolute uncertainty.

a.

i

total length of bar = 0.2 cm

Accept correct error bar in one of the points: OX= 1.8 cm OR OY= 5.8 cm (which is not a measured point but is a point on the interpolated line) OR OX= 5.8 cm.
Ignore error bar of OX.
Allow range from 0.2 to 0.3 cm, by eye.

 

ii

suitable line drawn extending at least up to 6 cm
OR
gradient calculated using two out of the first three data points

inverse of slope used

 

value between 1.30 and 1.60

If using one value of OX and OY from the graph for any of the first three data points award [2 max].
Award [3] for correct value for each of the three data points and average.
If gradient used, award [1 max].

 

iii

«the equation n= O X O Y » involves a tan approximation/is true only for small θ «when sinθ = tanθ»
OR
«the equation n= O X O Y » uses OI instead of the hypotenuse of the ∆IOX or IOY

OWTTE

 

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Core » Topic 1: Measurements and uncertainties » 1.2 – Uncertainties and errors
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