Transferring Energy Topic #6 Radiation, Conduction, Convection

Radiation Transfers Energy An object or material that can transfer energy to other sources is called an energy sourceAn object or material that can transfer energy to other sources is called an energy source Examples are: the sun, light bulbs, etcExamples are: the sun, light bulbs, etc Energy can be transferred, even though no matter has traveled between two things – this form of energy transfer is called radiationEnergy can be transferred, even though no matter has traveled between two things – this form of energy transfer is called radiation Energy that is transferred in this manner is called radiant energy or electromagnetic radiation (EMR)Energy that is transferred in this manner is called radiant energy or electromagnetic radiation (EMR)

Exactly how does radiant energy travel?Exactly how does radiant energy travel? Scientists have found that radiant energy travels and behaves like a waveScientists have found that radiant energy travels and behaves like a wave There are many different forms of EMR, such as: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma raysThere are many different forms of EMR, such as: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays All these forms share several characteristics: they behave like waves, they can be absorbed or reflected, they travel across empty space at the very same high speed of km/s!!!All these forms share several characteristics: they behave like waves, they can be absorbed or reflected, they travel across empty space at the very same high speed of km/s!!!

Conducting Energy Through SOlids In solids, where particles are close together, thermal energy can be transferred directly from one particle to anotherIn solids, where particles are close together, thermal energy can be transferred directly from one particle to another This process is called thermal conduction – where direct particle collisions cause transfer of energyThis process is called thermal conduction – where direct particle collisions cause transfer of energy Most metals, like gold and copper, are excellent heat conductorsMost metals, like gold and copper, are excellent heat conductors Some solids, like wood and glass, are much less efficient at transferring thermal energy – they are called heat insulatorsSome solids, like wood and glass, are much less efficient at transferring thermal energy – they are called heat insulators

Convection Thermal energy can be transferred in a third way by fluids – materials that can be poured or that flow from place to place (liquids and gases)Thermal energy can be transferred in a third way by fluids – materials that can be poured or that flow from place to place (liquids and gases) In convection, the warm fluid moves from place to place, carrying thermal energy with it.In convection, the warm fluid moves from place to place, carrying thermal energy with it. The movement of the fluid is called a convection current.The movement of the fluid is called a convection current. So why does this happen?So why does this happen?

How Convection Works! So why do fluids at different temperatures rise, sink and create convection currents?So why do fluids at different temperatures rise, sink and create convection currents? As materials expand when warmed up, the particles move farther apart, and make the fluid lighter or less dense.As materials expand when warmed up, the particles move farther apart, and make the fluid lighter or less dense. The opposite happens with cooled fluids – they become more dense as particles move together.The opposite happens with cooled fluids – they become more dense as particles move together. As warm fluid rises and move away from the heat source, it cools, becomes more dense and sinks back down and the cycle is repeated forming the current.As warm fluid rises and move away from the heat source, it cools, becomes more dense and sinks back down and the cycle is repeated forming the current.

Features of Energy Transfer Systems All energy transfer systems have five similar featuresAll energy transfer systems have five similar features 1) Energy source – something supplying energy to the system (mechanical – spring, chemical – diesel, nuclear – stars)1) Energy source – something supplying energy to the system (mechanical – spring, chemical – diesel, nuclear – stars) 2) Direction of energy transfer – always away from concentrated sources2) Direction of energy transfer – always away from concentrated sources 3) Transformations – energy doesn’t necessarily keep the same form as it is transferred from place to place3) Transformations – energy doesn’t necessarily keep the same form as it is transferred from place to place

Features of Energy Transfer Systems (cont.) 4) Waste heat – Almost all energy systems transfer at least a little thermal energy into the surroundings4) Waste heat – Almost all energy systems transfer at least a little thermal energy into the surroundings 5) Control systems – a furnace in your home transfers thermal energy to the air, but it doesn’t run all the time. A thermostat controls the energy transfer by turning the furnace on and off. Most systems have some sort of control5) Control systems – a furnace in your home transfers thermal energy to the air, but it doesn’t run all the time. A thermostat controls the energy transfer by turning the furnace on and off. Most systems have some sort of control Efficiency – about 85% of the energy from the fuel burned in a furnace is transformed into useful thermal energy – only about 5% of electrical energy in an incandescent bulb is transformed into light energy!!!!Efficiency – about 85% of the energy from the fuel burned in a furnace is transformed into useful thermal energy – only about 5% of electrical energy in an incandescent bulb is transformed into light energy!!!!