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Physics > 2.6 Electromagnetic Waves > Flashcards

2.6 Electromagnetic Waves Flashcards

1
Q

What are electromagnetic waves?

A

Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber without the need of a medium

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2
Q

Why are electromagentic waves different to mechanical waves?

A

Electromagnetic waves do not need a medium to travel through

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3
Q

What do electromagnetic waves form?

A

Electromagnetic waves form a continuous spectrum

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4
Q

Can electromagnetic waves travel through a vacuum?

A

Yes

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5
Q

What happens to the velocity of electromagnetic waves through a vacuum?

A

All electromagnetic waves travel at the same velocity through a vacuum as through air

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6
Q

At what speed do electromagnetic waves travel at?

A

3 x 108 m/s

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7
Q

How are the waves in the electromagentic spectrum grouped?

A

The waves in the electromagnetic spectrum are grouped in terms of their wavelength and their frequency

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8
Q

What does the energy waves transfer depend on?

A

The energy waves transfer depends on the wavelength of the waves

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9
Q

The shorter the wavelength, the ____________ the energy transferred

A

The shorter the wavelength, the higher the energy transferred

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10
Q

What are the types of electromagnetic waves, going from long wavelengths to short wavelengths

A

Going from longwavelengths to short wavelengths:

  1. Radio Waves
  2. Microwaves
  3. Infrared
  4. Visible Light
  5. Ultraviolet
  6. X-ray
  7. Gamma Ray
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11
Q

Which colour has the longest wavelength?

A

Red

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12
Q

Which colour has the shortest wavelength?

A

Violet

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13
Q

Why can humans only detect a limited range of electromagnetic waves?

A

Humans can only detect a limited range of electromagnetic waves as our eyes only detect visible light

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14
Q

Give 2 examples that show the transfer of energy by electromagnetic waves

A
  • Microwave Ovens transfer energy from a microwave source to the food in the oven, which heats it
  • Radiant heaters use infrared radiation to transfer energy from the heater to heat the surroundings
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15
Q

What happens when electromagnetic waves move from one medium to another

A

When electromagnetic waves move from one medium to another, the waves might be:
* Transmitted
* Absorbed
* Reflected
* Refracted

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16
Q

How does refraction occur?

A

Refraction occurs when the speed of the wave changes whilst moving from one substance to another, causing a change of direction

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17
Q

Why does refraction occur?

A

Refraction occurs because waves travel different speeds in different mediums

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18
Q

What are the rules of refraction?

A
  • The light ray changes direction towards the normal when it travels from air to glass
  • The ray changes direction away from the glass when it travels from glass to air
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19
Q

How are radio waves produced?

A
  • Radio waves can be produced by oscillations in electrical circuits
20
Q

How are radio waves produced?

A
  • Radio waves can be produced by oscillations in electrical circuits
  • This causes the transmitter to produce radio waves with the same frequency of oscillation
21
Q

How are radio waves absorbed?

What happens?

A

When radio waves are absorbed by a conductor, they induce an alternating current with the same frequency as the radio wave itself, so radio waves themselves can induce oscillations in an electrical circuit

22
Q

Give the 2 ways electromagnetic waves interact with atoms?

A

Electromagnetic waves are either absorbed or generated by atoms

23
Q

What happens when an electromagnetic wave is absorbed by an atom?

A

When an electromagnetic wave is absorbed, it can cause an electron to move to a higher energy level

24
Q

What happens when an electron returns or moves down to a lower energy level?

A

What an electron returns or moves down to a lower energy level, it can generate an electromagnetic wave

25
Q

Where do gamma rays originate from?

A

Gamma rays originate from changes in the nucleus of an atom

26
Q

Which elecromagnetic waves have hazardous effects on the human body?

A
  • Ultraviolet waves
  • X-rays
  • Gamma rays
27
Q

What do the effects of hazardous electromagnetic waves depend on?

A

The effects depend on the type of radiation and the size of the dose

28
Q

What is radiation dose?

A

Radiation dose is a measure of the risk of harm to the body

29
Q

How is radiation dose measured?

A

Radiation dose in sieverts

30
Q

How many millisieverts in 1 sievert (Sv)

A

1000 millisieverts (mSv) = 1 sievert (Sv)

31
Q

What are the hazardous effects of ultraviolet waves?

A

Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer

32
Q

How can humans be protected from ultraviolet waves?

A

Skin creams can be used to block ultraviolet waves and prevent them from reaching your skin

33
Q

What are the hazardous effects of gamma rays and X-rays?

A

X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer

34
Q

What are the uses of radio waves?

Why are they suitable for that purpose?

A

Television and Radio
- Because they travel long distances before being absorbed
- They reflect off the ionosphere in the Earth’s atmoshpere so they can be sent across very long distances around the Earth

35
Q

What are the uses of microwaves?

Why are they suitable for that purpose?

A

Satellite Communications and Cooking Food
- They pass through the Earth’s atmoshpere withour reflection or refraction
- They are absorbed by the water molecules in food, which then heat up

36
Q

What are the uses of infrared (waves)?

Why are they suitable for that purpose?

A

Electrical heaters, Cooking food, Infrared cameras
- Easily absorbed by surfaces
- Emitted by hot objects

37
Q

What are the uses of visible light (waves)?

Why are they suitable for that purpose?

A

Fibre optic communications
- Fibre optic cables contain thin strands of glass which reflect visible light inside to carry pulses of light across cables

38
Q

What are the uses of ultraviolet (waves)?

Why are they suitable for that purpose?

A
39
Q

What are the uses of X-rays and gama rays?

Why are they suitable for that purpose?

A

Medical imaging and treatments
- They are highly penetrating

40
Q

What are the differences between each colour in the visible light spectrum?

A

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency

41
Q

What does the colour of an opaque object depend on?

A

The colour of an opaque object is determined by which wavelengths of light are more strongly reflected

42
Q

What happens if all wavelengths are reflected equally in an opqaue object?

A

If all wavelengths are reflected equally, then the object appears white

43
Q

What happens if all wavelengths are absorbed by an opqaue object?

A

If all wavelengths are absorbed the objects appears black

44
Q

How do colour filters work?

A

Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)

45
Q

How would a surface look red in terms of wavelength?

A

When the surface absorbs all the wavelengths except for the red component of the white light, which is reflected off the surface

46
Q

If an object transmits light, what could it be known as?

A
  • transparent
  • translucent

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