Refraction of waves Flashcards
Refraction occurs when light enters a different medium, its speed changes:
- Light slows down as it enters a more dense medium - it deviates towards the normal.
- Light speeds up as it enters a less dense medium - it deviates away the normal.
What does the refractive index indicate?
The refractive index indicates the amount of deviation - the greater the deviation, the higher the refractive index.
Refractive (n) Eq.
refractive (n)
Why does dispersion occur?
- Dispersion occurs because each colour slows down by a differnt amount when white light enters a medium such as glass, plastic or water, and speeds up by a different amount on leaving.
- Dispersion occurs because different colours have different speeds in a medium and have different difractive indices. This means each colour has a different angle of refraction.
When light passes from a more dense medium into a less dense medium.
The angle of refraction is larger than the angle of incidence.
What is the critical angle?
- The critical angle is the angle of incidence in the more dense medium that produces an angle of 90° in the less dense medium.
When the angle of incidence is less than the critical angle.
Most of the light is refracted out of the glass.
If the critcal angle is exceeded.
The light is totally internally reflected.
Optical fibres are used:
- To carry telephone conversations and computer data as pulses of laser light.
- In endoscopes to look inside the body without surgery.
Total internal reflection only happens when:
- A ray of light travels from one medium towards another with a lower refractive index (for example, glass to air glass to water) so that the angle of refraction reaches 90° as the angle of incidence is increased.
- The angle of incidence is greater than the critical angle.
The higher the refractive index.
The lower its critical angle.
