Activity 1. Refractive index
- Explore the textual information below:
Refractive index
Light propagates incredibly fast in a vacuum: 3∙ 108 m/s (300 million meters per second or 300 thousand kilometres per second). It moves almost as fast in air but slows down considerably in water, glass and other transparent substances. The refractive index of a substance expresses how many times slower light moves in it than in a vacuum. It is a measure of how much a substance slows down light. The refractive index is calculated by dividing the speed of light in a vacuum by the speed of propagation of light in a given medium.
A refractive index is a number that indicates the ratio of the two speeds – the speed of light in a vacuum to the speed of refracted light in a substance, therefore it has no unit.
- Compare the speed of propagation of light in different substances using the refractive index given in Table 1. Speed of light propagation in different optical media. Work in Excel.
|
Table 1 |
|
|
substance |
speed of light in km/s |
| Diamond | 124 000 |
| ice | 229 000 |
| glass | 200 000 |
| vacuum | 300 000 |
| water | 225 000 |
| air | almost 300 000 |
To download: Worksheet Speed of light propagation in different optical media
- Record the answers to the questions and problems in the Excel table.
Questions and tasks:
- In which medium does light propagate the slowest?
- In which medium does light propagate the fastest?
- In which medium does light propagate almost as fast as in a vacuum?
- Complete Table 2: Sort the substances according to the speed of light propagation. Start with the medium in which light spreads the fastest.
- Complete Table 2: Calculate the refractive index of the substance and record the result in the last column of the table.
- Compare the refractive index of different substances. Express the relationship between the magnitude of the refractive index and the magnitude of the speed of refracted light.
- Based on the previous findings, choose the correct option from the highlighted words in the sentence: The greater the refractive index of a substance, the slower/faster light propagates through it.
