| English | Total internal reflection |
|---|---|
| Bahasa Melayu | Pantulan dalam penuh |
| 中文 | 全内反射 |
Definition
The complete reflection of light back into the denser medium when the angle of incidence exceeds the critical angle.
In exam terms
Total internal reflection is the complete reflection of a light ray back into the denser medium when the angle of incidence is greater than the critical angle. No light refracts out; all of it obeys the law of reflection at the boundary.
Two conditions must both be met: light travels from a denser to a less dense medium, and the angle of incidence exceeds the critical angle. A correct sentence: light inside the optical fibre strikes the wall above the critical angle, so total internal reflection keeps it inside. It is used in optical fibres, periscopes and prisms.
Do not confuse it with ordinary reflection
Do not confuse total internal reflection with ordinary reflection from a mirror. Ordinary reflection happens at any angle off a reflecting surface and loses some light; total internal reflection needs the two conditions above and reflects 100% of the light, giving no loss.
In Paper 2, a state the two conditions question expects both bullet points, and an explain how an optical fibre works question wants: light enters the core, hits the boundary above the critical angle, and is totally internally reflected repeatedly along the fibre.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)