Light and Sound Flashcards
What type of wave are light waves?
Transverse waves (as they are part of the EM spectrum)
What is reflection?
When a wave hits a boundary between two different media (materials), but does not pass through and instead is sent back, staying in the same medium
For sound waves this is an echo. For light waves, it is when you see a reflection such as a mirror
What is refraction?
When a wave passes between two different media (materials) of different densities and undergoes a change in direction
If light is being refracted, the two different media must both be transparent
What is the law of reflection?
- When a wave is reflected, the angle between the incident ray (original ray) and normal, and the reflected ray and the normal will be equal
- So angle of incidence = angle of reflection
The normal is a straight line drawn through the middle where the two points meet at the boundary, and is perpendicular to the boundaries
How do you draw a reflection ray diagram?
- The normal should be drawn
- The angle of incidence and the angle of reflection must be drawn accurately, be labeled i and r and must be equal
What happens to light when it enters a more dense material?
- The wavespeed and the wavelength decrease
- Light bends towards the normal
The frequency here is staying constant meaning colour does not change and wavespeed and wavelength are directly proportional
What happens to light when it enters a less dense material?
- Its wavespeed and wavelength will increase
- Light bends away from the normal
What happens to light if it is passing into a different material but is doing so perpendicular to the boundary (it is going along the normal)?
It does not change direction at all
How do you draw a refraction ray diagram?
- Draw in the normals, they must be perpendicular to the surface of the boundary
- As the light passes into a more dense material, the light will keep going but bend towards the normal - The angle of incidence and the angle of refraction (in) will be formed
- As it passes out of the dense material, the light will keep going but bend away from the normal, and the angle of emergence and the angle of refraction (out) will be formed
The angles are always between the normal and the waveline
What happens to the angle of refraction (in) as the angle of incidence increases?
The angle of refraction increases
What is the equation which links the angle of incidence, angle of refraction and the refractive index of the material the waves entering?
The refractive index is a number related to the speed of light within the material, so is related to the density. Objects with higher densities will have a higher refractive index (diamond has 2.4)
- Refractive index = Sin (angle of incidence)/Sin (angle of refraction - in)
- N = Sin (i)/Sin (r)
What is total internal reflection?
When light passes from a dense to a less dense material, but instead of being refracted, it is all reflected
What are the conditions for total internal reflection to occur?
- The angle of angle of incidence must be greater than critical angle (c)
- It must be passing from a more dense to a less dense medium
The law of reflection still applies so the angle of incidence must equal the angle of reflection during TIR
What is critical angle (c)?
When the angle of emergence/refraction (in) is 90 degrees or greater and fails to leave the medium in which it entered, the angle of incidence has reached or exceeded critical angle (c)
How is total internal reflection used in optical fibres?
- Light is sent through the fibre, and each time it hits the wall of the fibre it is totally internally reflected and continues to travel down the fibre, even if there is a bend
- This means it can be used to see inside peoples bodies and transmit information
