Electromagnetic Waves

Question 1

What are electromagnetic waves and how do they transmit energy?

Answer 1

Electric and magnetic disturbances that transfer energy from one place to another

They cause oscillations in electric and magnetic fields and therefore do not require particles to transfer energy

Question 2

Complete the sentence:

Electromagnetic waves have the same _____ but different _______ and _______.

Answer 2

Electromagnetic waves have the same speed but different wavelengths and frequencies.

Question 3

Compare the wavelength and frequency of a gamma ray to that of a radio wave

Answer 3

• Gamma rays have the shortest wavelength and highest frequency
• Can have wavelengths as short as 10^-15m
• Radio waves have the longest wavelength and lowest frequency
• Can have wavelengths of more than 10,000m

Question 4

The electromagnetic spectrum is continuous. What does this mean?

Answer 4

The frequencies and wavelengths at the boundaries are approximate as the different parts of the spectrum are not precisely defined

Question 5

Complete the sentence:

Different wavelengths of electromagnetic radiation are…

Answer 5

…reflected, absorbed, or transmitted differently by different substances and types of surface

Question 6

Complete the sentence:

The higher the frequency of the electromagnetic wave…

Answer 6

…the more energy it transfers

Question 7

What is the wave speed at which electromagnetic waves travel through space?

Answer 7

300 million m/s

Question 8

How do we see a mixture of all the colours?

Answer 8

As white light

Question 9

Which colour/electromagnetic wave has the longest wavelength?

Answer 9

Red

Question 10

What type of electromagnetic wave do remote controls for TVs and CD players use?

Answer 10

Infrared radiation

Question 11

How and why are microwaves used in communications?

Answer 11

Microwave transmitters produce wavelengths that are able to pass through the atmosphere

They are used to send signals to and from satelites and within mobile phone networks

Question 12

What are radio waves used for?

Answer 12

To transmit radio and TV programs and to carry mobile phone signals

Question 13

What are the dangers of radio waves and microwaves?

Answer 13

They can penetrate your skin and are absorbed by body tissue. This can heat internal organs and may damage them

Question 14

What are the dangers of infrared radiation?

Answer 14

It is absorbed by skin. Too much will burn your skin

Question 15

How are radio waves produced (using electricity) for use in communications?

Answer 15

• An alternating voltage applied to an aerial emits radio waves with the same frequency as the alternating voltage
• When the waves are recieved they produce and alternating current in the aerial with the same frequency as the radiation recieved.

Question 16

What are ‘bands’?

Answer 16

The parts of the radio wave and microwave spectrum used for communications

Different bands are used for different communication purposes

Question 18

Complete the sentence:

The shorter the wavelength of waves…

Answer 18

… the more information they can carry, the shorter their range, the less they spread out

Question 19

How do mobile phones work?

Answer 19

They communicate with a local mobile mast using wavelengths just on the border between radio waves and microwaves

They are usually referred to as microwaves

Question 20

Are mobile phones safe to use?

Answer 20

Some scientists think that the radiation from mobile phones may affect the brain, especially in children

More research is needed to evaluate whether or not this is true

Question 21

What are optical fibres and how do they work?

Answer 21

• Very thin glass fibres
• Used to transmit signals carried by visible light or infrared
• The signals travel down the fibre by repeated total internal reflection

Question 22

Why are optical fibres useful in communications?

Answer 22

Because they use visible light/infrared. Tsis means they are able to carry more information and are more secure than radio/microwave trasmissions

Question 23

What is the Doppler effect?

Answer 23

It’s the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.

https://www.youtube.com/watch?v=Y5KaeCZ_AaY

Question 24

What happens when the wave source moves away from the observer?

Answer 24

The observed wavelength increases and the frequency decreases

Question 25

What happens when the wave source moves towards the observer?

Answer 25

The observed wavelength decreases and the frequency increases

Question 26

How can the Doppler effect be demostrated?

Answer 26

With sound waves.

For example, an ambulence siren will sound different depending on whether it’s moving towards or away from you

Towards = higher pitch, away = lower pitch

Question 27

What is red-shift?

Answer 27

• Light observed from distant galaxies has been ‘shifted’ towards the red end of the spectrum
• This means that the frequency has decreased and the wavelength has increased
• The further away the galaxy, the bigger the red-shift. This suggests that distant galaxies are moving away from us and that the most distant galaxies are moving the fastest
• This is true no matter what direction you look. All the galaxies are moving away from each other, so the whole universe is expanding from a singular point.

Question 28

What is blue-shift?

Answer 28

The reverse of red-shift.

Observed in galaxies emitting dark lines in their spectra. Would indicate that galaxies are moving towards us (but they aren’t)

Question 29

What is the Big Bang Theory?

Answer 29

The theory that the universe began as a massive explosion from a single point (singularity) and has continued expanding outwards ever since

Question 30

What is CMBR and how does it provide evidence for the Big Bang Theory?

Answer 30

• If the universe began with a Big Bang, high energy gamma radiation would have been emitted. As the universe expanded, this would have become lower-energy radiation
• Scientists have discovered microwaves coming from every direction in space
• This is cosmic microwave background radiation, the radiation produced just after the Big Bang occured
• So far, the Big Bang theory is the only way to explain the existence of CMBR