Cooking With Waves

8/14/2019 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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Cooking With Waves