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RADIATION...HOW WE GET HEAT FROM THE
SUN
· Heat can be transferred by conduction, convection and radiation.
· Heat is radiated as infrared waves (electromagnetic waves that travel
in straight lines at the speed of light)
But why is radiation different from conduction and convection?…read more

Slide 3

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HOW IS RADIATION DIFFERENT FROM
CONDUCTION AND CONVECTION?
· It doesn't need a substance to travel through
· This means it can happen in a vacuum ­ like space
· This is how we get heat from the sun
· Radiation can only occur in transparent materials, like air, water and
glass
· Surface colour and texture affect the amount of radiation emitted or
absorbed.…read more

Slide 4

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ALL OBJECTS EMIT AND ABSORB HEAT
RADIATION
· This happens continually. The hotter an object is, the more heat it
radiates.
· Cooler objects absorb heat radiation from hotter objects.
· This makes their temperature increase.
· We can feel radiation; for example, when the sun shines through a
window onto you.…read more

Slide 5

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GOOD / BAD ABSORBERS AND EMITTERS
· Good ­ matt black surfaces
· Bad ­ light coloured surfaces
· Bad ­ smooth and shiny surfaces…read more

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WHY IS HEAT RADIATION IMPORTANT IN
COOKING?
· Things such as toasters use infrared radiation to cook food.
· Grill pans can be lined with shiny foil to increase the radiation being
reflected onto the food.
· Microwaves use microwaves to heat food (no surprise there)
· However, foil cannot be used in microwaves...that's both dangerous
and stupid because it reflects the microwaves away from the food,
and can cause sparks.…read more

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