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Flashcards in P1.10/11 - Light Deck (16)
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1

What is total internal reflection?

You will remember that when light moves from one medium to another it refracts. For example. if light moves from glass into air it bends away as it leaves the glass but a small amount of light is reflected back into the glass. IF the light hits the boundary at a big enough angle of incidence, all of the light stays within the glass. It is reflected internally. This is total internal reflection.

2

Total internal reflection happens if the angle is over the ______ ____ for the material.

critical angle

3

The effect of Total internal reflection can be seen when something travels from a less dense material to another. What two requirements need to be met for total internal reflection to occur?

-The angle of the light is greater than the critical angle.
-The light is travelling in the denser of the two materials.

4

What are optical fibres or fibre optics?

They are very fine glass cables that can be used to transmit large amounts of information or help doctors peer inside a patients body without cutting them open.

5

How do waves travel along fibre optics?

Waves travel along fibre optics through total internal reflection. They enter the fibre and hit the edge at an angle greater than the critical angle. It does this every time it hits the edge until it reaches the other end.

6

Why is fibre optic broadband must faster than using normal phone lines?

Pulses of visible light or infrared radiation are sent down optical fibres when using fibre optic broadband. This allows large amounts of data to be sent very quickly.

7

What is an endoscope?

An endoscope is a medical instrument that can produce an image of inside the body through a tiny key-hole rather than cutting the patient open.

8

How does an endoscope work?

Inside an endoscope there are several bundles of optic fibres. The endoscope is inserted into the body and visible light is sent along the optic fibres. The light illuminates the inside of the body then reflects back down the separate cables and is sent to a TV screen for the doctor to assess.

9

What is Morse Code?

Morse Code is a series of flashes used to represent different letters. It is a very early form of communicating with light over long distances. These flashes could be relayed from one station to another and travels very quickly. Morse Code can also be thought of as an early digital signal.

10

What is a laser?

A laser is a narrow beam of light. The light does not spread out much as it travels long distances. The light from a laser is only one colour whilst normal light is many colours.

11

What are some uses of lasers?

-Used in surgery and dental treatments
-Guiding weapons
-CD's, DVDs, and blue-ray players
-Cutting materials e.g steel plates

12

What do we mean by the light in a laser is in phase?

The waves emitted from a laser light all have the same frequency and they are in sync with each other. This is why we say the light is in phase.

13

Laser lights are described as a source of coherent _________ light.

monochromatic

14

What does monochromatic mean?

Waves of a single wavelength or frequency and only contains one colour.

15

What is a light described as when it does not spread out very much?

It is described as having a low divergence.

16

How is a laser used to read CD's and DVDs?

Information on CD's and DVDs are stored in a series of pits. There are billions of pits on the average CD. The disc spins and a laser is reflected from its surface. There is no reflection when the light enters the pit, so the detectors reads a series of light pulses. It is like an advanced version of Morse Code.o