Heat and Energy

Heat and Energy

Heat and Temperature

This cup of coffee will ____ ____ because it is _____ ____ heat energy into the surroundings.

This drink (taken out of the fridge) will _____ ___ because it is _____ ___ heat energy from the surroundings.

Heat is a type of energy that will flow from a warm area to a colder one. For example…

Words – giving out, warm up, taking in, cool down

Kinetic Theory

Solid

Liquid

Gas

The particles in a solid vibrate about fixed positions. The bonds are strong, and solids have a fixed shape.

The particles in a liquid are close together, but are free to move past one another. Liquids flow. There are still strong bonds between the particles, which must be broken before particles can escape and evaporate.The particles in a gas are far apart, and can move past each other freely. Gases flow. There are no bonds between the particles.

Conduction is all about when heat is transferred through a _________. The heat is passed on by ___________ in the molecules. These vibrations get BIGGER when the solid has more ENERGY (i.e. when it is being __________).

Metals are _______ conductors than non-metals. This is because the heat is carried by free ________ that can carry the energy around the metal and give it to other electrons and ions.

Conduction

Words – vibrations, electrons, solid, heated, better

Heating a non-metal

Heating a metal

ConvectionConvection is all about when a gas or liquid (“fluid”) moves and carries heat with it. When the fluid is heated it ____________. This means that it will become less __________ than the colder fluid around it. Because of this the warmer fluid will try to “_______” over the colder fluid, and this is why warm air rises. This is called a convection ___________. This is how heat reaches us from the ___________ in this room.In CONDUCTION the heat was passed on by VIBRATIONS in a

SOLIDIn CONVECTION the heat is passed on by the FLUID

expanding, rising and TAKING THE HEAT with it

Words: expands, radiators, dense, heated, current, float

Some questions on convection…

1) Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily.

2) Explain why a hot air balloon rises in the air.

3) Explain why an ice cube floating at the top of a drink will cool all of the drink.

RadiationI’m very hot!I’m cool!

Thermal (_________) radiation is the transfer of heat energy by electromagnetic _____. It can pass through a _____ (which is how we get heat from the ____). Anything hot emits thermal radiation.Heat is radiated by the surface – the bigger the surface area, the more radiation.Dark, matt surfaces absorb AND emit a lot ______ heat radiation than white or shiny surfaces.Silvered surfaces ________ almost all heat radiation.

Words – Sun, reflect, infrared, waves, more, vacuum

Evaporation

Evaporation requires energy. If the most energetic particles evaporate, the average energy of the remaining particles is reduced, and the temperature drops.

The Vacuum FlaskPlastic cap filled with foam.

Reduces conduction.

Silvered on inside to reflect heat radiation back to hot contents.

Silvered on outside to reflect heat radiation away

from cold contents.

Double-walled glass with vacuum between. Stops all conduction and convection.

Specific Heat CapacityThe specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1 degree Celcius.

Energy transferred = mass x specific heat capacity x temperature change (joules) (kg) J/kgoC oC

1. How much energy is needed to raise the temperature of 2 kg of water by 10 oC? (specific heat capacity 4200 J/kgoC)

2. How much energy is needed to achieve the same temperature change in 2 kg of copper? (specific heat capacity 380 4200 J/kgoC)

EnergyThere are nine forms of energy:

ElectricalChemical

HeatLightSound

NuclearKinetic (movement)

Gravitational potentialElastic potential

Energy can never be created nor destroyed – it is only ever converted from one form to another

Electrical Light (useful)Heat (wasted)

Energy Transfer Diagrams

House insulation

Draught excluders

Double glazing

Loft insulationCavity wall insulation

U-ValueTells us how much energy passes through per second.The lower the U-value the better the insulator.

House insulationType of insulation Cost Annual amount

saved

Loft insulation £400 £80

Double Glazing £2,000 £50

Cavity wall ins. £600 £60

Draught excluder £40 £20

1) Which type of insulation costs the most?2) Which type of insulation is the most effective?3) Which type is the most “cost effective”?4) Which type pays for itself after 40 years?