All objects emit and absorb infrared radiation. The hotter an object is the more infrared radiation it radiates in a given time.
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How do materials affect infrared radiation?
Dark, matt surfaces are good absorbers and good emitters of infrared radiation. Light, shiny surfaces are good reflectors of infrared radiation.
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What is a vacuum?
Any region that doesn't contain any particles
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Explain the particles in a solid
The particles are held together, vibrating in a fixed position so it has a fixed volume and shape. They do not flow easily.
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Explain the particles in a liquid
The particles can move/slide past each other, they have no fixed shape and can flow easily.
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Explain the particles in a gas
The particles move around at random faster and are farther apart. They don't have a fixed shape, can flow and have a lower density.
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Explain the process of conduction
It occurs mostly in solids. The particles near the heat source gain more kinetic energy and vibrate faster. This energy is passed to neighboring particles and the energy is transferred through the solid.
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Explain conduction in metals
When metals are heated their delocalised electrons gain kinetic energy and move through the metal, transferring energy by colliding with other particles.
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Insulators
Poor conductors. Materials such as wool and fibreglass are good insulators as they contained trapped air.
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Explain the process of convection
Occurs in fluids and is the circulation of fluids caused by heating. When a fluid is heated it expands, becomes less dense and rises. The warm fluid is replaced by cooler, denser fluid.
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Explain the process of evaporation
When a liquid turns to gas. When the particles with the most kinetic energy escapes from the liquid's surface and enters the air. The average kinetic energy of the remaining particles is less so the temperature decreases.
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What increases the rate of evaporation?
Increasing the surface area of the liquid and increasing the temperature of the liquid
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Explain the process of condensation
When a gas turns to a liquid. Takes place on cold surfaces such as windows and mirrors.
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What increases the rate of condensation?
Increasing the surface area of the liquid and reducing the surface temperature
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What are the factors which the rate of energy transfer depends on?
The shape, size and type of material of the object; the objects surface area; the temperature difference between the object and its surroundings.
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How to maximise the rate of energy transfer to keep things cool
Use good conductors; things painted dull black.
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How to minimise the rate of energy transfer to keep things warm
Use good insulators; things shiny and white; prevent convention currents by trapping air in small pockets
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What is the specific heat capacity?
The amount of energy required to raise the temperature of 1Kg of the substance by 1°C
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What are U-values?
They tell us how much energy per second passes through the material. The lower the U-value the better the material is as an insulator
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How do solar heating panels work?
They contain water which is heated by radiation from the sun which may then be used to heat buildings or provide hot water. They are cheap to run as they do not use fuel but are expensive to buy and install.
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What are ways of minimising the rate of energy transfer in homes?
Fibreglass loft insulation to reduce conduction; cavity wall traps air to reduce convection; double glazed windows to reduce conduction; draught proofing to reduce convection; aluminum foil behind radiators to reflect IR back into the room
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Other cards in this set
Card 2
Front
How do materials affect infrared radiation?
Back
Dark, matt surfaces are good absorbers and good emitters of infrared radiation. Light, shiny surfaces are good reflectors of infrared radiation.
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