P5 - Refraction

Question 1

What is refraction & what is it caused by?

Answer 1

• Refraction is when waves change direction as they enter a different medium.
• This is caused entirely by the change in speed of the waves.

Question 2

What feature of the wave is changed during refraction?

Answer 2

• Wavelength is changed.

* Frequency doesn’t change.

Question 3

What happens when a wave crosses a boundary between two substances?

Answer 3

• 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.

Question 4

What happens if the wave speed decreases as it enters medium?

Answer 4

• If the wave-speed bends towards the normal.

Question 5

What happens if the wave speed increases as it enters as medium?

Answer 5

• If the wave speed increases as it enters a medium, it bends away from the normal.

Question 6

What happens when light passes from air to glass?

Answer 6

• 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.

Question 7

What happens to light when it enters glass?

Answer 7

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.

Question 8

What is the refractive index?

Answer 8

• 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.

Question 9

What happens when waves hit a boundary along the normal?

Answer 9

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.

Question 10

What is the absolute refractive index of a material?

Answer 10

Speed of light in a vacuum/Speed of light in a medium.

Question 11

What is the refractive index of air?

Answer 11

1