The purpose of this experiment is to determine the refractive index of Perspex plastic. All of these variables are related through Snells Law.

Aim:

To determine the index of refraction of Perspex plastic

Background Information:

When light enters a transparent medium from another, the light appears to bend inside the medium it enters (refer to fig 1 below). This is known as refraction and is caused by the change in speed of light as it enters the medium (Reed, 2009). The angle of refraction depends on the medium’s refractive index. The purpose of this experiment is to determine the refractive index of Perspex plastic. All of these variables are related through Snell’s Law.

Fig 1. Diagram of light (from Britanica Inc)

Snell’s Law states (Weisstein, 2007):

Where: = refractive index of the medium where light is leaving (no units)

= refractive index of the medium where light is entering (no units)

= angle of incident (measured in degrees o)

= angle of refraction (measured in degrees o)

For this experiment, light will be travelling from air to the Perspex plastic. The angle of incident is the independent variable and the angle of refraction is the dependent variable. The refractive index of air is 1. Using Snell’s Law, the refractive index of Perspex plastic will be determined by rearranging the equation to obtain:

The refractive index for Perspex plastic is known to be 1.49 (A. L. Hyde Company, 2007).

Raw Data:

Below is a raw data table of refraction for a Perspex plastic prism when varying the angle of incident

The uncertainty of the protractor is estimated to be half of the smallest division, which is ±0.5o. However, there are 2 sides to the protractor. Therefore it is doubled which is ±1.0o

Table 1. Raw Data of Results of the Angel of Refraction with the Angle of Incident:

Processed Data:

Table 2. Processed Data of Average Angle of Refraction with the Angel of Refraction: