Cooking With Waves
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Transcript of Cooking With Waves
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Cooking with WavesCooking with Waves
This is a group of waves ranging from radio waves through light
waves down to X-Rays and gamma rays
They all travel at the speed of light and differ only in wavelength
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Microwaves and Infrared Waves inMicrowaves and Infrared Waves in
CookingCooking
Microwaves have wavelengths of a few cm. Infrared waves have
much smaller wavelengths. Both will cook food
Microwave ovens are much cheaper to run than ordinary ovensbecause ou dont have to heat the oven itself
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Penetration of WavesPenetration of Waves
Microwaves penetrate about 1 cm. into the food.
They are well absorbed by water molecules
Infrared dont penetrate at all; they only cook the surface
The rest of the food (the inside) is heated by conduction
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Microwaves and Infrared WavesMicrowaves and Infrared Waves
Microwaves
Wavelength 3 cm
Absorbed by water Penetrate into food about
1 cm.
Travel at speed of light
Part of EMS
Infrared Waves
Very small wavelength
All hot or warm objectsgive off infrared waves
Only cook the surface offood
Travel at the speed of light Part of EMS
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Microwaves in CommunicationMicrowaves in Communication
Mobile phones use microwaves
The transmitters and receivers need to be in line of sight
Because microwaves cant bend round corners
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Microwaves in Long Distance communicationsMicrowaves in Long Distance communications
A microwave signal is sent to a satellite by a ________ on Earth
The signal is received by a __________ on the satellite
The signal is retransmitted to the Earth by a _______ on the satellite
Sky TV is transmitted using microwaves
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Infrared SignalsInfrared Signals
Infrared waves are used in a cordless mouse and in remote controls
Since burglars give off heat they are also use in security alarms
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Diffraction of WavesDiffraction of Waves
If waves go past an obstacle they are diffracted; this means they
spread out in all directions.
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Diffraction of Radio WavesDiffraction of Radio Waves
Sometimes radio waves are diffracted round hills enabling a good
reception
Only radio waves with a long wavelength are diffracted
Microwaves are not diffracted
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RefractionRefraction
When a wave moves from one substance to another e.g. from air
into water
It changes speed (either slows down or speeds up)
This means it usually changes direction
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Refraction of Radio Waves by the IonosphereRefraction of Radio Waves by the Ionosphere
Radio waves with a long wavelength are refracted so much by the
ionosphere that they return to Earth
If they strike an ocean they can be reflected back into the
atmosphere and travel even further
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Diffraction Of Radio WavesDiffraction Of Radio Waves
If the wavelength of the radio wave is long it sees the Earth as an
obstacle and it is DIFFRACTED. This means it bends round theEarth and oes further.
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Advantages of WirelessAdvantages of Wireless
CommunicationCommunication
No wires are needed (unlike conventional phone
Therefore portable
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Problems with CommunicationsProblems with Communications
1. Obstacle like hills can sometimes cause a loss of signal
2. The wave sees the edge of the dish as an obstacle and bends round it;
i.e. it is _____________. Therefore some of the energy is lost
3. If a wave is refracted (bent) by the atmosphere it may miss the satellite
4. Atmospheric conditions (storms) can disrupt signal
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LasersLasers
Lasers produce a narrow intense beam of light waves
The waves are all the same frequency
The waves are all in phase
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LasersLasers
CDs are read by lasers.
The laser beam is reflected by the shiny surface or NOT reflected
by the pits
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Skin Cancer and UV radiationSkin Cancer and UV radiation
Ultra violet waves from the Sun can cause SKIN cancer
If you are dark skinned there is less of a risk because
Dark skins absorb the UV better and stop it getting to the inner
layers of the skin where it can do the damage
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Sun CreamsSun Creams
Sun Protection Factor is how many times longer you can stay safely
in the Sun without burning if you use the cream.
E.g. if you could only stay safely in strong sun for 20 minutes
without any cream and then you used SPF 5 you could stay in the
sun safely for 100 minutes
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