Cooking and Communicating with Waves Flashcards
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
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
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)
Do hotter or colder objects emit more infrared
Hotter emits more
Why are jacket potatoes wrapped in tin foil
Reduces infrared radiation it emits as shiny objects reflect infrared
It cools more slowly
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
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
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
Analogue signals:
Vary continually in amplitude
Many values within fixed range
Digital signals:
Only two values ON and OFF in a series of pulses
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
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
What are advantages of optical fibres
Rapid data transmission
Light pulses for transmission
Multiplexing
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
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
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
Why can’t we rely on microwaves to diffract around obstacles
Wavelength is not large enough
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
How do remote controls work
Device uses sets of digital signals/codes to control different functions
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
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
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
