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Physics > Electromagnetic waves > Flashcards

Electromagnetic waves Flashcards

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1
Q

Do higher or lower frequency waves have more energy?

A

Higher frequency waves

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2
Q

Do longer or shorter wavelength waves have more more energy?

A

Shorter wavelength

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3
Q

What is the critical angle?

A

The angle at which total internal reflection occurs and no refraction takes place

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4
Q

What is the angle of incidence?

A

The angle at which light enters a object

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5
Q

What conditions are needed for refraction?

A

The angle of incidence must be greater than the critical angle

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6
Q

What pathway will light take if the angle of incidence is equal to the critical angle?

A

The light will be refracted along the boundary

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7
Q

What conditions are needed for TIR (Total internal reflection?

A

The angle of incidence must be greater than the critical angle

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8
Q

What is meant by the term monochromatic?

A

Made up of only ONE colour of light, with one single frequency

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9
Q

What is meant by the term phase difference?

A

The difference between one wave and another when you compare the cycles of of each wave

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10
Q

What is meant by the term divergence?

A

How much light waves spread out as they travel

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11
Q

Why do laser produce an intense beam of light?

A

They carry a large amount of energy and have a low divergence so they concentrate light in a small area.

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12
Q

Why do lasers produce a coherent beam of light?

A

They produce a monochromatic light with a single frequency which has waves that are all in phase

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13
Q

True or false;

Laser produce waves that are ‘In phase’

A

True

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14
Q

In regards to the pathway of light when entering different mediums, what is the normal line?

A

The pathway that light would take if it didn’t enter a medium of a difference density and refract

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15
Q

What is morse code an example of?

A

A digital code

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16
Q

True or false;
Digital codes are a method of representing information from only two different states.
Give an example to support your answer

A

True

Eg. dots/dashes, on/off, up/down, 1/0 etc.

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17
Q

What are the two states of a digital wave?

A

Peaks and troughs, they can a different values

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18
Q

Why do digital waves suffer from less interference?

A

Because they have only two values, unlike analogue signals which have continuous values, and therefore interference on the waves can be easily removed because it is still clear what the states and values of the digital waves actually are.

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19
Q

Why are infrared waves only suitable for short distance communication?

A

Because they are easily obstructed, so wouldn’t be suitable for long range communication

20
Q

What is multiplexing?

A

Multiplexing is when communications from several sources are transferred through the same cable, they are then filtered out again at the other end of the cable

21
Q

What is demultiplexing?

A

The process which separates (filters out) individual signals which have been transmitted over a single data stream, alongside signals from several other sources.
It is the opposite, and reverse process, of multiplexing?

22
Q

How does the curvature of the earth impede a signal? How do we combat this?

A

Because waves travel in straight lines and therefore will not follow the curvature of the earth and therefore we must use reflection (using either the ionosphere or satellites) to direct waves around the earth

23
Q

Why do microwaves only require small receivers but radio waves require larger receivers?

A

As microwaves have a shorter wavelength, they only require a small receiver however, as radio waves have a much larger wavelength, they need a larger receiver

24
Q

Why is total internal reflection used in fibre optics?

A

To transmit signals around curves in the fibre optic cables

25
Q

Why are fibre optic connections much faster than standard connections?

A

Because they transmit huge amounts of information, using multiplexing, at the speed of light.

26
Q

Which type of wave penetrates the ionosphere? Why?

A

Microwaves, because they have a higher frequency and short wavelength so they contain more energy and therefore they aren’t affected by a low density gas, such as ionosphere, which they penetrate. Satellites are required to reflect them back towards surface transmitters

27
Q

Which type of wave reflects off the ionosphere? Why?

A

Radio waves, because they have a lower frequency and long wavelength so they contain less energy and therefore they will refract as the density in the atmosphere changes, eventually they will reflect of the low density ionosphere and travel back towards the surface

28
Q

What process could the effect of the ionosphere be broadly likened to?

A

Total internal reflection

29
Q

Is the ionosphere dense?

A

No, it is not very dense

30
Q

What happens to gases in low temperatures?

A

They begin to sink

31
Q

What happens to the ionosphere in low temperatures?

What effect does this have?

A

As it is a low density gas, it begins to sink and therefore is closer to the earths surface. This restricts the range of radio waves reflecting off the ionosphere and can create problems when sending radio waves over long distances

32
Q

Give some examples of uses for radio waves?

A
  • Televisions and radios

- Computers, bluetooth and Wi-Fi

33
Q

Give some examples of uses of microwaves?

A
  • Cooking

- Mobile phones

34
Q

Give some examples of uses for inferred waves?

A
  • Cooking
  • TV remotes (Short range communication)
  • Automatic lights and burglar alarms (Infrared waves detect heat)
35
Q

Out of radio waves and microwaves, which has the most energy?

A

Microwaves, because they have a higher frequency and low wavelength.

36
Q

Name a disadvantage to communicating using microwaves?

A
  • They require line of sight communication and are obstructed or scattered by various means.
  • They do not diffract
  • Microwaves could interfere with other microwaves working off similar frequencies
37
Q

What are microwaves scattered by?

A

They are obstructed and scattered by; Objects/ buildings, hills, poor weather and storms, large bodies of water and the curvature of the earth.

38
Q

Which type of electromagnetic wave requires line of sight communication?

A

Microwaves

39
Q

Name two characteristics of electromagnetic waves?

A

1) They are all transverse waves

2) They all travel at the same speed in a vacuum

40
Q

What are the possible health risks associated with microwaves?

A

There is limited evidence to suggest that microwaves have a heating effect of the brain, this would be particularly detrimental to children who have thinner skulls than adults

41
Q

Name some advantages of wired communication, as oppose to wireless communication?

A
  • Wired communication can make use of multiplexing to send vast amounts of data at rapid speeds.
  • No interference in the final signal, this can be an issue with wireless communication
42
Q

How do radio waves send signals around the curvature of the earth?

A

Because they reflect off the ionosphere to travel back to the surface

43
Q

Give some advantages of radio wave communication?

A
  • Reflects off the ionosphere to travel around the curvature of the earth
  • Will diffract around objects
44
Q

Why can’t radio waves transmit large amounts of information?

A

Because they have a low frequency.

45
Q

Which two types of electromagnetic waves require ‘line of sight’ communication

A

Infrared waves and microwaves

Physics (3 decks)

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