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Heat Radiation
· Heat energy can be transferred by radiation, conduction (transfer of particles-
solids) or convection (transfer of particles- liquids and gases)
· It is the transfer of heat energy by infrared radiation (IR)
· Infrared radiation (emission of electromagnetic waves) can be emitted by solids,
liquids and gases continuously from the surface of an object. Any object can
both absorb and emit IR whether or not conduction or convection are taking
place
· Hotter than surroundings emits more radiation than it absorbs
· The hotter an object is, the more radiation it radiates in a given time. You can
feel the IR if you stand near something hot
· Cooler than surroundings absorbs more radiation than it emits
· The bigger the temperature difference between a body and its surroundings,
the faster energy is transferred by heating…read more

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Radiation Depends On...
· Surface colour & Texture:
-dark, matt surfaces absorb IR better than light, shiny surfaces such as
gloss white or silver
-they emit much more radiation at any given temperature
-light, shiny surfaces reflect a lot of IR e.g. vacuum flasks- silver inner
surfaces to keep heat in or out (dependent on whether it's storing a hot or
cold liquid)
· Solar hot water panels contain water pipes under a black surface
-radiation from the sun is absorbed by the black surface to heat the
water
-the water is used for washing or pumped radiators…read more

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Kinetic Theory
· Solids: strong forces of attraction hold the particles together in a fixed, regular
arrangement. Particles don't have much energy so vibrate about their fixed
positions
· Liquids: weaker forces of attraction between the particles so they're close
together but can move past each other to form irregular arrangements. More
energy than particles in a solid- move in random directions at a low speed
· Gases: almost no forces of attraction between the particles. They have more
energy than particles in liquids and solids- free to move and travel in random
directions at high speeds
· When you heat a substance, you give its particles more kinetic energy- vibrate
or move faster which is why solids melt and liquids boil…read more

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Conduction
Conduction of heat energy is the process where vibrating particles pass
on their extra kinetic energy to neighbouring particles
· This continues throughout a solid and gradually some of the extra
kinetic energy/heat is passed all the way through a solid- rise in
temperature at the other side of the solid- increased heat radiating
from surface
· Faster in denser solids because the particles are closer together and
so will collide more often and pass energy between them
· Materials that have larger spaces between their particles conduct
heat energy much more slowly- insulators…read more

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Metals Are Good Conductors
· Metals conduct so well because the electrons are free to move inside the
metal
· At the hot end the electrons move faster and collide with other free
electrons, transferring energy. The other electrons pass on their extra
energy to other electrons etc.
· Because the electrons can move freely, it's a much faster way of
transferring the energy through the metal than slowly passing it between
neighbouring atoms
· Conduction is more efficient in a short, fat rod than a long thin rod
because the distance is shorter for the electrons to transfer the energy…read more

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