Reflection and refraction physics unit 2 communication Flashcards
what does law of reflection say ?
Angle of incidence = Angle of reflection
what is refraction ?
when waves like light pass from one medium to another the speed of them changes. This causes the angle they are travelling to change.
what happens when light goes from air into glass ?
When light goes from air into glass it slows down because glass is a denser medium than air. This causes the ray to bend towards the normal due to the decrease in speed . This means the angle of refraction is always smaller than the angle of incidience when light enters a denser medium.
what happens when light goes from glass to air ?
when light goes from glass to air it speeds up . This causes the ray to bend away from the normal. This means that the angle of refraction is always bigger than the angle of incidience.
what does the refractive index of a material tell us ?
The refractive index of a material tells us how much light will slow down when it goes from air into that material.
what is a problem with refractive indexes ?
It is difficult to measure the speed of light experimentally. But you can measure the angles of incidence and refraction.
what is total internal reflection ?
When light is reflected back at the boundary between glass and air.
What is a critical angle ?
The point at which refracted ray follows the line of the barrier.
How do you calculate the refractive index from a critical angle ?
Refractive index ( n) = 1/ sin c
what happens when light goes from air into glass ?
Light bends towards the normal and slows down
What happens when light goes from glass into air ?
Light bends away from the normal and it speeds up.
what happens to light at critical angle ?
Light is refracted at 90 degrees
what happens to light at total internal reflection ?
The angle of incidience must be greater than the critical angle at the barrier.
What are optical fibres ? ( 6 marks )
Optical fibres are very thin flexible glass fibres that can carry light signals.
Optical fibres have a high refractive index core surrounded by a lower refractive index cladding
Cladding also acts to protect optical fibres from scratches which could allow light to escape
What are the benefits of changing from copper cables to Fibre optics ? ( 6 marks )
Don’t get hot like copper cables because light signals convert almost no energy into heat.
Cheaper to produce than copper cables because glass is cheaper than copper.
The signal travels a long way very quickly Because light travels very fast.
Can carry more information because light has a very short wavelength.
what can a pulse do ?
a pulse can take a variety of different paths through a fibre. This means that a single pulse ofl ight can spread out over some time.
How can we prevent the pulse broadening effect?
Single modal fibres have a core diameter of a few wavelengths so the light can only travel through one path
If you cut your yellow light into squares and glued them back together randomly how would they look ?
The fibre optic cables taking light inside the body can be in any order. we call this incoherent
Would a doctor be able to identify an ulcer from an incoherent picture ?
The fibre optic cables taking the picture back to the doctor must remain in the same order. We call this coherent.
describe how endoscopes work ( 6 marks)
An endoscope consists of two bunches of optical fibres . One bundle transmits light down the tube and the other transmits pictures back to the doctor. The optical fibres transmitting light can Incoherent. The optical fibres can be randomly arranged. The optical fibres transmitting the picture must be coherent . The optical fibres must stay in the same order. Laser light can be sent down an optical fibre . The light can be focused on a very small area and be used to cut away diseased tissue.
what do analogue signal carry and have ?
Analogue signals have an amplitude which constantly varies with time.
What do digital signals have ?
digital signals are a series of pulses consisting of just two states , on and off
what is digital sampling ?
digital sampling is the process by which an analogue wave is converted into a digital signal
what happens in digital sampling ?
The voltage of the analogue signal is sampled at set time intervals. The voltages are converted into a binary code of 0 and 1s . This is called a digital signal. The digital signal is transmitted.
what happens in digital sampling ?
The more frequently we sample the closer the sound or image is to the original
what are the advantages of digital signals over analogue ?
- can be regenerated so they travel longer distance
- The quality of the reception is better because there is less interference
- can carry more channels because they carry more information per second
- can be encrypted so they are more secure
