Cooking and Communicating with Waves Flashcards Preview

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Flashcards in Cooking and Communicating with Waves Deck (22):
1

Explain cooking with microwaves

The electromagnetic waves penetrate about 1cm into food and are absorbed by fat and water molecules. Must be stirred

Kinetic energy increases making temperature rise and food cooks

1

Why is food cooked quicker in microwaves

Microwaves have longer wavelengths than infrared
food cooks quicker in microwave than in oven
The wavelengths are also more easily absorbed by water and fat

2

How do objects cook using infrared cooking

The wave is absorbed by particles in surface
kinetic energy increases and so does temperature
Surface particles transfer energy to particles in the centre by conduction
Some surface particles can get damaged (burnt)

2

Do hotter or colder objects emit more infrared

Hotter emits more

3

Why are jacket potatoes wrapped in tin foil

Reduces infrared radiation it emits as shiny objects reflect infrared

It cools more slowly

5

Mobile phones transmit information over large distances that are in LINE OF SIGHT

What does this mean

Transmitter and receiver must have no obstacles between them

Places with poor signal are not in line of sight

6

What do both digital and analogue signals suffer from and how is it removed for digital

Interference,noise

Can be removed from digital by filtering. Stations have well separated frequency with less space

7

Why can microwave signals be poor

It may be due to
Large obstacle such as building or mountain
Signal being affected by body of water
Curvature of the earth
Signal getting weaker as it travels further

8

Analogue signals:

Vary continually in amplitude
Many values within fixed range

9

Digital signals:

Only two values ON and OFF in a series of pulses

10

What are wifi advantages and disadvantages

No wiring,don't need to be connected directly to transmitter
Portable
Access signals while moving
However it NEEDS AERIAL

11

Long distance communication depends on what two factors

Reflection-
Longer wavelength radio waves are reflected by electrically charged ionosphere (enables international programme transmission)
Refraction-
Waves changing direction at different layers of Earth's atmosphere

These both happen in the ionosphere. The techniques keep signals in the atmosphere preventing signals escaping into space

12

What are advantages of optical fibres

Rapid data transmission
Light pulses for transmission
Multiplexing

13

Positives and negatives of Digital Audio Broadcasting (digital signals)

More stations and less interference
Multiplexing
BUT
poorer audio quality than FM
Not all areas of country are covered

14

What is the concern about microwave signals

Children using mobiles-thinner skulls,brain may get damaged
People living near transmission lines are putting health at risk

NO EVIDENCE

15

How can signal loss be reduced

By putting transmitters and receivers closer together
Positioning them on high ground with no obstacles between them and curvature of earth has less effect

16

Why can't we rely on microwaves to diffract around obstacles

Wavelength is not large enough

17

What can infrared waves be used for (in the home)

How do infrared sensors work

Tv remotes
Short distance links between computers and printers eg wifi

Infrared sensors can detect body heat and sounds a burglar alarm

18

How do remote controls work

Device uses sets of digital signals/codes to control different functions

19

What are two negative effects on signal quality

Diffraction (changes to direction and intensity of waves) -
Diffraction at edge of transmission dishes causes wave to spread out resulting in signal loss

Refraction-
Can lead to loss of signal at layers of atmsophere

20

If signals are sent to satellites above atmosphere, how can they travel long distances around the world

Signals are 'bounced' (received and retransmitted) to the next satellite and travel around the world

21

Why can interference not happen with digital signals

Each station is well separated (less bandwidth so more space)
Processing enables random signals to be filtered out before they are turned into light or sound