Perspex Block

Aim:

1. To investigate the relationship between the angle of θ Air and the angle of θ Medium using a semicircular Perspex block and a beam of light

2. To determine the refractive index of a Perspex block.

Apparatus:

The diagram above shows the apparatus layout. Shown in the diagram is a semicircular Perspex block, a ray box, a single slit, a sheet of white paper, a protractor and a power supply.

Method:

The semicircular Perspex block was placed onto a blank piece of paper and was traced in pencil. First, the centre of the semicircle was measured using a ruler. Then, normal was drawn when the beam of light was shone through the block undeviated. The incident rays were drawn at 10o intervals from 10o to 80o . This was measured with the protractor. From the ray box, a beam of light was shone through the single slit along each line in turn. Small crosses were used to mark the refracted rays. The angles of refraction were measured and recorded. A graph of the results was plotted. The refractive index was determined by the graph gradient. After each measurement, the alignment was checked by shining the ray along the normal to ensure the semicircular block was consistently in the correct place.

Results:

The results were recorded in the table below. A line graph was plotted and is at the end of report.

θ Air (o)

± 0.5 θ Med (o)

± 0.5 Sin θ Air

±0.01 Sin θ Med

±0.01 N=Sin θ Air

Sin θ Med

10 6 0.17 0.10 1. 66

20 12 0.34 0.21 1. 65

30 18 0.50 0.31 1. 62

40 24 0.64 0.41 1.58

50 29 0.77 0.48 1.58

60 34 0.87 0.56 1.55

70 37.5 0.94 0.61 1.54

80 40 0.98 0. 64 1.53