Light Waves Flashcards
Are light waves transverse or longitudinal?
Transverse
Do all waves reflect? Give examples Water waves Electromagnetic waves Infrared waves Light waves and ultraviolet X ray waves Gamma rays?
All waves reflect but different types of waves will reflect differently from different surfaces. For example:
Water waves will reflect from solid objects
Electromagnetic waves will nearly reflect off all metal surfaces except gamma rays and some x rays which passes through metals:
Infrared waves will reflect off shiny or white surfaces and will be absorbed by black and Matt surfaces
X-rays also reflect off metal surfaces and be absorbed by some materials
Gamma ray waves can pass through metals because they have wavelengths smaller than the gaps between atoms and so are not reflected by materials
Note: waves generally reflect from surfaces when the wavelength is greater than any gaps.
What is the incoming wave in a diagram?
Incident wave
Using arrows you can show that it is incoming So going down
What is the reflected wave called?
Reflected wave
Using arrows you can show it is reflected so the arrow is pointing up
Why do we use a normal when drawing Ray Diagrams?
We use a dotted line drawn at right angles to the surface where the ray hits the surface. This is called a normal and we measure all angles of the rays to this line. We use a normal because if it has a curved surface it would be hard to measure.
What is the angle called between the incident ray and the normal and what is the symbol?
Angle of incidence and uses the symbol I
What is the angle called between the reflected ray and the normal?
Angle of reflection and uses the symbol r
In all cases of reflection, the law of reflection applies… the equation
The angle of incidence = the angle of reflection
I = R
It is true in all reflections of all waves
What is refraction?
When waves change speed when they change medium
What happens when the wave enters another medium?
The waves change wavelength and direction at the boundary where the speed changes as the wave passes over the block.
What happens to light waves when they change mediums?
They slow down when they enter water, glass or plastic compared to their speed in air and speed up again when they return to air so refraction occurs.
Do you use a normal when drawing ray diagrams for refraction?
We need to measure the angle accurately and so we add a mor,al to allow this.
What happens when a light waves enters a glass or Perspex block?
Light travels fastest in air and so slows down when enters a transparent material
When light enters the block it will slow down and the ray will bend towards the normal
We measure both its angle of incidence and angle of refraction
When the ray of light leaves the block it will speed up again and bend away from the normal.
If the light ray hits the surface at a right angle for example along the normal it will still change speed but it will not change direction.
If we need to label the angle of incidence and angle of refraction where would they go?
The angle of incidence is the angle in the air and the angle of refraction is the angle in the outer medium.
What is the refractive index?
A measure of how many times slower the light is in that material compared to the speed of light in the air.
