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?
What is total internal reflection?
It is the reflection of the total amount of incident light at the boundary between two media.
When can total internal reflection take place?
- When rays of light are travelling towards a boundary with a less optically dense medium.
- The angle of incidence has to be large than the critical angle.
What does less optically dense mean?
It means that the medium has a lower refractive index.
How can you draw total internal reflection?
What is the critical angle?
It is the angle at which light is no longer able to pass through the boundary between two mediums and instead gets completely reflected back into the original medium.
How can you draw the critical angle?
How do you draw what happens when i is equal to the critical angle?
What is an optical fibre?
Is a very thin piece of fibre composed of two different types of glass. The centre is made of a glass that has a higher refractive index surrounded by a glass with a lower refractive index. This is to ensure that the light doesn’t escape.
How do optical fibres work?
Due to the fact that the fibres are so narrow, light entering the inner core always strikes the boundary of the two glasses at an angle that is greater than the critical angle (meaning total internal reflection will always occur).
Why does the optical fibre have glass with a lower refractive index around it?
To ensure that the light doesn’t escape.
What things use total internal reflection in everyday life?
- Binoculars
- Endoscopes
- Bicycle or car reflectors
How does total internal reflection happen in prisms?
Light entering the prism is totally internally reflected twice. The light emerges from the prism travelling back in the direction from which it originally came.
What is the equation used to find the critical angle?
sin c = 1/n
What kind of waves are sound waves?
Longitudinal.
What does the type of wave sound waves are tell us about it?
That they can be reflected and refracted.
