P1e: Cooking and Communicating Using Waves.

All radiations in the electromagnetic spectrum can be dangerous but they also have many uses. Infrared radiation and microwaves are useful for cooking since they cause heating in objects that absorb them. Microwaves are used for mobile phone communications. This item develops ideas about the properties of infrared and microwave radiation and examines their dangers and uses.

 

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Which colour and texture is best for emitting and absorbing infrared radiation?
Black and Dull.
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Which colour and texture is bad at emitting and absorbing infrared radiation?
White and Shiny.
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What do all objects give out and take in?
Infrared radiation.
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What increases the amount of infrared radiation an object gives out?
The temperature of an object. The hotter = more it emits
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Do all hot objects glow? Give examples.
No. The heating element in a toaster and an electric fire does, but an iron does not.
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What surface reflects infrared radiation?
A shiny surface.
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What happens when an object absorbs infrared radiation? Give an example.
The temperature of the object increases. E.g. food begins to cook when it's surface absorbs infrared radiation.
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Talk about the wavelengths and frequency of microwave radiation compared with visible light.
Lower frequencies and longer wavelengths.
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Microwaves can't be seen but what can they cause?
Burns if they are absorbed by body tissues.
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What do microwaves rely on? and how do they warm up food?
Microwave ovens rely on the ability of microwaves to penetrate about 1 cm into food. They are absorbed by water in the food, causing it to warm up.
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What's the safe limit set by 'British Standard' for microwaves?
50 watts per square metre at 5cm.
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What does '50 watts per square metre at 5cm' mean? (Microwaves)
This means that measurements of microwave power taken at 5 cm from the microwave must be less than 50 watts per square metre.
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What do microwaves have to protect us from the harmful effects of their radiation?
microwave ovens have metal cases and the glass doors have a metal mesh.
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What do microwaves pass through?(2) What are they reflected by?(1) What can absorb microwaves?(1)What is the effect of absorbing this?
Microwaves pass through plastics and glass, but are reflected by metals. The water in living cells can also absorb microwave radiation. As a result, they can be killed or damaged by the heat released.
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Which two ways does the use of mobile phones mean people are exposed to microwave radiation?
to the head from the aerial in the phone and to the body from transmitters in base station masts.
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Which type of radiation do mobile phones use to communicate with their base stations?
low intensity microwave radiation.
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Complete the sentence: Microwaves can be used to _______ information over _____ distances, although some areas have ____ _______.
Microwaves can be used to transmit information over large distances, although some areas have poor signals.
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What does SAR stand for?
Specific Absorption Rate.
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What is the limit on the amount of microwave radiation that can be emitted by mobile phones?
The SAR should be no more than 2 watts per kilogram.
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What have studies into possible health effects of mobile phones and masts concluded? What precautions can be made?
No conclusive evidence that they damage your health,but cuz millions of people use mobiles,many believe it's sensible 2 advise public 2 take precautions.There are concerns about children using mobile phones&about people using them very often.
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How far can microwaves from phones penetrate body tissues?
To a depth of a few centimetres.
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What does body tissues absorbing microwaves cause to happen?
Microwaves give up their energy to body tissues. This can cause a small amount of heating, about 0.1°C. This is much less than if you stand in sunshine.
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How is kinetic energy transferred to the centre of the food when cooking?
By convection or conduction.
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What happens to the kinetic energy of particles when the radiation is absorbed?
They increase.
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Complete the sentence: The ______ the frequency of an electromagnetic _____, the ______ the energy it _______ for a given amplitude.
The higher the frequency of an electromagnetic wave, the greater the energy it transfers for a given amplitude.
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Which radiation has a higher frequency? Infrared or Microwaves? What does this mean it can do?
Infrared. It can transfer enough energy to break chemical bonds. Microwaves cannot.
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Where in the house does a wireless router work best?
In the loft.
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Where are transmitters usually placed?
High up, on masts.
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What four facts may affect how far apart transmitters can be?
signals interfering with each other, large buildings and obstacles, need for transmitters and receivers to be in the line of sight, and poor weather surface water scatter signals.
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Why do microwaves get blocked by large buildings and other obstacles?
Because there is no refraction of microwaves around them.
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Other cards in this set

Card 2

Front

Which colour and texture is bad at emitting and absorbing infrared radiation?

Back

White and Shiny.

Card 3

Front

What do all objects give out and take in?

Back

Preview of the front of card 3

Card 4

Front

What increases the amount of infrared radiation an object gives out?

Back

Preview of the front of card 4

Card 5

Front

Do all hot objects glow? Give examples.

Back

Preview of the front of card 5
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