| English | Refractive index |
|---|---|
| Bahasa Melayu | Indeks biasan |
| 中文 | 折射率 |
Definition
A measure of how much a medium slows down light, equal to the speed of light in a vacuum divided by its speed in the medium.
In exam terms
The refractive index n of a medium measures how much it slows down light. It is defined as the speed of light in a vacuum divided by the speed of light in the medium: n = c ÷ v.
It has no unit because it is a ratio of two speeds.
It can also be found from angles using Snell's law: n = sin i ÷ sin r, where i is measured in the vacuum/air side. For example, if sin i = 0.80 and sin r = 0.53, then n = 0.80 ÷ 0.53 = 1.5.
A larger n means a denser medium and greater bending.
Do not confuse it with density
Do not confuse optical density (linked to refractive index) with mass density (mass ÷ volume, in kg m⁻³). A medium with a higher refractive index is optically denser, but that does not always mean it has a higher mass density.
In Paper 2, define refractive index as the ratio of the speed of light in vacuum to its speed in the medium, and a calculate question expects you to use n = sin i ÷ sin r or n = real depth ÷ apparent depth, showing the working and stating the answer with no unit.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)