# Energy Transfer By Heating

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## Conduction

Heat energy can be transferred in 3 ways- Conduction, Convection & Radiation

Conduction:

• Occurs in solids ( mainly)
• Heat energy makes the particles on one side vibrate
• This makes them pass on some of the enery to other particles, which vibrate and pass on some energy
• Metals are good conductors because they have electrons which are free to move & pass on more of the energy
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## Convection

Convection:

• Occurs in liquids and gases only
• The energy is transferred to the water
• The particles near the water heat up and start moving faster
• This means that there is more distance between the particles- the water expands & becomes less dense
• The heated particles rise above the cooler ones
• The heated particles cool and fall back down, repeat
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## Radiation // Evaporation & Condensation

• All objects emit infrared radiation
• The hotter an object, the more it radiates
• Dark, matt surfaces absorb & emit more radiation
• Light, shiny surfaces reflect most of the radiation on them

Evaporation:

• Particles escape from the liquid
• The particles gain energy and start moving around
• The fastest particles can sometimes break free from the body
• This decreases the average particle energy- the temperature of the liquid falls

Evaporation can be sped up if there is More energy, Less liquid or a Bigger surface area

Condensation can be sped up if there is a Bigger surface area or a Lower surface temperature

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## Energy Efficiency In the House

Payback Time:

• The time taken to recover the cost of the object from what you have saved on it:
• To work out payback time: Initial cost / Annual saving

U-Values:

• Tells us how much energy passes through different materials per second
• The bigger the U-Value, the better conductor

Specific Heat Capacity:

• The energy needed to increase the temperature of 1kg of something by 1 degree
• Energy = mass x S.h.c. x Temp. change
• E ( J ) = m ( kg ) x S.h.c ( j/ kg  C ) x (  C )
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