P5 - Refraction Flashcards
What is refraction & what is it caused by?
- Refraction is when waves change direction as they enter a different medium.
- This is caused entirely by the change in speed of the waves.
What feature of the wave is changed during refraction?
- Wavelength is changed.
* Frequency doesn’t change.
What happens when a wave crosses a boundary between two substances?
- Wave such as light travel at different speeds in substances with different densities.
- When a wave crosses a boundary between two substances ( e.g from glass to air ) it changes speed.
What happens if the wave speed decreases as it enters medium?
• If the wave-speed bends towards the normal.
What happens if the wave speed increases as it enters as medium?
• If the wave speed increases as it enters a medium, it bends away from the normal.
What happens when light passes from air to glass?
- When light passes from air into the glass of a window ( a denser medium ), it slows down, this causes the light to refract towards the normal.
- When the light reaches the “glass to air “ boundary on the other side of the window, it speeds up and refracts away from the normal.
What happens to light when it enters glass?
When light enters glass it slows to about 2/3 of its normal speed.
I.e. its speed is about 2 x 10^8 M/S rather than 3 x 10^8 M/S.
What is the refractive index?
- The ratio of the speed of light in a vacuum to the speed of light in a medium is called the refractive index of the medium ( 3/2 for glass ).
- It is basically a measure of the amount of bending, the higher the refractive index, the more the light bends when it enters or leaves the medium.
What happens when waves hit a boundary along the normal?
When waves hit a boundary along the normal, i.e. at exactly 90 degrees, then there will be no change in direction, there will still be a change in speed and wavelength though.
What is the absolute refractive index of a material?
Speed of light in a vacuum/Speed of light in a medium.
What is the refractive index of air?
1
