3 Light waves Flashcards
What are luminous objects?
Objects that emit their own light.
What kind of waves are light waves?
Transverse waves.
Can light waves be reflected and refracted?
Yes, all waves can.
What is reflection?
Wave reflection occurs when energy traveling in the form of waves through a medium hits an obstacle and then bounces back.
What is the law of reflection?
The angle of incidence is equal to the law of reflection.
How do you draw a diagram showing reflection?
What is the normal line?
It is a line which is drawn at right-angles to a surface.
What can you use reflection for?
Periscopes.
How do you explain how reflection works in a periscope?
Rays from the object strike the first mirror at a 45* to the normal line, these is then reflected again at 45, creating 90, so they are then reflected onto the second mirror where they again strike at 45* each to create a straight line out.
How can you change the direction of a ray of light?
A mirror.
What kind of waves reflect and refract?
All kinds of waves.
What is refraction?
The change in the direction of a wave passing from one medium to another
How do you draw a diagram showing refraction?
What happens during refraction?
As a ray enters a glass block, it slows down and is refracted towards the normal line. As the ray leaves the block it speeds up and is refracted away from the normal line.
What happens if the incidence ray strikes the boundary between the two media at 90*?
The ray continues without a change of direction.
What affects how much the incidence ray bends away from the normal line?
When it travels from a less dense medium to a denser medium.
What is the refractive index?
A measure of the change in speed a wave experiences when it travels across the boundary between two media, the index also describes how much the direction changes.
What is the equation for the refractive index?
n = sin i / sin r
What are the steps you take to investigate the refractive index for a glass block?
- Shine a ray of light onto one of the sides of the glass block, so that the ray emerges on the opposite side of the block. Trace over the line that the ray follows.
- Draw around the glass block before removing it.
- Draw in the direction of the ray that travelled inside the glass block and link it up the the incidence and emergence ray you previously drew before.
- Draw the normal line.
- Measure the angles of incidence and refraction.
- Use the equation n = sin i/sin r to find the refractive index of the glass.
- Plot the results on a graph of sin i to sin r.
What are the steps you take to investigate the refractive index for a semi-circular block?
- You are investigating total internal reflection.
- By carefully increasing and decreasing the angle at which the ray strikes the flat edge of the glass block, we can discover the smallest angle at which most of the light is refracted along the edge of the glass block.
- This angle is the critical angle.
How do you draw total internal reflection in a semi circular block?
What are the steps you take to investigate total internal reflection in a triangular prism?
- If you shine a ray of light into a prism it will strike the surface at an angle of 45. The critical angle for glass is about 42 so the ray will be internally reflected. The two 45* will show that the ray will be reflected through an angle of 90*.
How do you draw total internal reflection in a right-angled triangle?
How do you draw total internal reflection in a non-right angled triangle?
