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GCSE questions on refraction and TIR

Q11. Nick investigated the refraction of light at the boundary between air and glass.

The photo shows the ray box he used.

(a) The ray of light from the ray box should be as narrow as possible.

Explain why using a wider ray would give less accurate results than using a narrower ray.

It is harder to judge where the centre of a wider ray is. This causes a larger uncertainty in the measurements taken relating to the position of the ray (increasing the random errors in the experiment).

[2 marks]

(b) The graph below shows the results.

(c) Estimate the angle of refraction when the angle of incidence is 80°.

Show on the graph how you obtained your answer.

The first mark was for a smooth line of best fit drawn and extrapolated to 80 degrees (see graph)

Any answer from 40o to 43o got you the second mark.

[2 marks]

(d) Describe a method the student could have used to obtain the results shown in the above graph.

 

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

The design/plan would lead to the production of a valid outcome.

All key steps are identified and logically sequenced.

5 - 6 marks
Level 2:

The design/plan would not necessarily lead to a valid outcome.

Most steps are identified, but the method is not fully logically sequenced.
3 - 4 marks
Level 1:

The design/plan would not lead to a valid outcome.

Some relevant steps are identified, but links are not made clear.
1 - 2 marks
Level 0:

No relevant content
0 marks

 

Indicative content:

place a glass block on a piece of paper

draw around the glass block

use the ray box to shine a ray of light through the glass block

mark the ray of light entering the glass block

mark the ray of light emerging from the glass block

join the points to show the path of the complete ray through the block

and draw a normal line at 90 degrees to the surface

use a protractor to measure the angle of incidence

use a protractor to measure the angle of refraction

use a ray box to shine a ray of light at a range of different angles (of incidence)

increase the angle of incidence in 10 degree intervals

from an angle of incidence of 10 degrees to an angle of incidence of 70 degrees

allow use of optical pins instead of a ray box

[6 marks]

(e) The student repeated each measurement three times.

When the angle of incidence was 40° the three measured values for the angle of refraction were:

28°
25°
22°

 

Estimate the uncertainty in the angle of refraction when the angle of incidence was 40°.

Show clearly how you determined your estimate.

Method 1

Find Average:

(28 + 25 + 22) /3 = 25

Work out variation from it:

28 - 25 = 3

Therefore uncertainty is ±3o

 

OR

Method 2

Max - Min:

28 - 22 = 6

Halved:

6 ÷ 2 = 3

Therefore uncertainty is ±3o

 

 

[2 marks]

(f) Tick the one of the following properties of a light wave that changes when it is refracted.

 

Colour
Frequency
Velocity

[1 mark]

(Total 13 marks)