P1d Cooking with Waves
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Interpret information on the electromagnetic spectrum to include microwaves and infrared radiation.
Recognise that warm and hot objects emit radiation:
- hotter objects emit more radiation;
- black dull objects emit more radiation.
Recognise that infrared radiation is absorbed by the surface of an object causing an increase in temperature:
- black surfaces are good absorbers of radiation.
Recognise that microwaves cause heating when absorbed by water and this is the basis of the microwave oven.
State that mobile phones use microwave signals.
Describe some concerns about children using mobile phones.
Describe properties of microwaves:
- penetrate (about 1cm) into food;
- are reflected by metal;
- can cause burns when absorbed by body tissue;
- go through glass and plastics.
Describe properties of infrared radiation:
- heats the surface of the food;
- is reflected by shiny surfaces.
Recognise that microwaves are used to transmit information over large distances that are in “line of sight”:
- some areas and places have poor signals. Recognise that there may or may not be dangers:
- to residents near to the site of a mast;
- to users of mobile phones.
Explain how microwaves and infrared transfer energy to materials:
- microwaves absorbed by water particles in outside layers increasing their KE;
- infrared is absorbed by all particles on the surface increasing their KE;
- energy transferred to centre of food by conduction or convection.
Describe how the energy associated with microwaves and infrared depend on their frequency and relate this to their potential danger.
Describe how diffraction and interference of microwaves can cause signal loss:
- limited distance between transmitters;
- high positioning of transmitters;
- nuisance of obstacles affecting signals.
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