A student measured the angle of incidence i and the angle of refraction r for a ray of light passing through a transparent block - Leaving Cert Physics - Question 2 - 2018

To draw the graph:

1. Axes: The x-axis represents the angle of incidence (i in degrees) and the y-axis represents the angle of refraction (r in degrees).

2. Plot Points: Using the provided data, 6 points should be plotted:

   • (20, 14)
   • (30, 20)
   • (40, 26)
   • (50, 31)
   • (60, 35)
   • (70, 38)

3. Line of Best Fit: Draw a straight line through the origin that has a good fit with the plotted points.

The relationship observed in the graph shows that as the angle of incidence increases, the angle of refraction also increases. This is indicative of Snell's Law, which states that the light refracts at angles depending on the medium.

4. Explanation of the Graph: The graph verifies this relationship by showing a linear correlation, indicating that the sine of the angle of incidence is proportional to the sine of the angle of refraction.

To determine the refractive index from the graph, calculate the slope (n):

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

1. Slope Calculation: If you take two points from your graph, for example,

   • Point 1: (20°, 14°)
   • Point 2: (70°, 38°) The slope can be calculated as: $\text{slope} = n = \frac{y_2 - y_1}{x_2 - x_1} = \frac{38 - 14}{70 - 20} = \frac{24}{50} = 0.48$

2. Value of n: The calculated index of refraction is approximately 1.50, which suggests the material of the block possesses this refractive index.

If the incident ray is perpendicular to the block, it would not bend as it enters the material. Instead, the ray would pass straight through without any change in its angle. This is because the angle of incidence would be 0 degrees, resulting in the angle of refraction also being 0 degrees.