Calculations Calculate the sine of the angle of incidence (sin i ) and the sine of the angle of refraction (sin r ).
Tabulation of Data Table 13.2
i / ° r / ° sin i sin r
Graph Plot a graph of sin i, against sin r, with sin i on the y-axis.
Conclusion The straight line through the origin verifies Snell’s law, that sin i is proportional to sin r.
Use Graph The refractive index (n) of the prism can be calculated from the graph. If sin i is on the y-axis and sin r on the x-axis then the refractive index is equal to the slope of the line of best fit (n slope).
Explanation Based on the equation for refractive index we get:
n sin i sin r Qsin i n sin r
Using the equation of the line y mx c, given that c 0 because the line passes through the origin, it is clear that the refractive index is equal to the slope.
Precautions Increasing the angle of incidence will reduce the percentage error. Plotting more points will produce a more accurate graph. Use a sharp pencil for all lines. Make sure that the pins A and B are spaced well apart, and so are C and D.
Note
The incident and emergent rays are parallel. The refractive index (n) can be calculated by formula instead of using a graph. Calculations For each pair of readings, sub the values of sin i and sin r into the formula
