Physics Revision: Heating Processes

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Kinetic Theory

Specific Heat Capacity- The amount of energy required to change the temperature of 1kg of the substance by one degree Celsius

ENERGY=MASS X SPECIFIC HEAT CAPACITY X TEMPERATURE CHANGE

Specific latent heat of vaporisation=The amount of energy required to change the state of 1kg of the substance from liquid to vapour with no change in temperature.

ENERGY=MASS X SPECIFIC LATENT HEAT OF VAPORISATION

Specific latent heat of fusion=The amount of energy needed to change 1kg of the substance from solid to liquid with no temperature change.

ENERGY=MASS X SPECIFIC LATENT HEAT OF FUSION


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Energy Transfer by Heating Part 1

Energy can be transferred by conduction and convection

CONDUCTION=VIBRATING PARTICLES PASS ON KINETIC ENERGY TO NEIGHBOURING PARTICLES

CONVECTION= WHEN PARTICLES MOVE FROM HOTTER REGIONS TO COLDER REGIONS, ALL DUE TO A CHANGE IN DENSITY

Energy can also be transferred through evaporation and condensation

EVAPORATION= LIQUID TO GAS

CONDENSATION=GAS TO LIQUID

The cooling effect from evaporation: The faster liquid particles which have more kinetic energy break away from the weak attraction between particles in the liquid, and so the liquid is cooler because the average kinetic energy is now decreased. Factors which affect evaporation include surface area, temperature, and a draught of air on the liquid.

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Energy Transfer by Heating Part 2

The rate an object transfers energy depends on:

  • Its surface area and volume
  • The material that the object is made of
  • The nature of the surface the object is in contact with.

The bigger the temperature difference between an object and its surroundings, the faster the rate energy is transferred by heating

Most substances expand when heated, this can be useful or hazardous.

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Infrared radiation

1. All objects emit and absorb infrared radiation

2.The hotter an object is the more infrared radiation it radiates (in a given time)

3. Dark,matt surfaces are good absorbers and good emitters of infrared radiation

4. Light,shiny surfaces are poor absorbers and poor emitters of infrared radiation.

5. Light,shiny surfaces are good reflectors of infrared radiation.

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Energy Transfers and efficiency

When energy is transferred it can be usefully transferred or wasted

Wasted energy is transferred to the surroundings, and the further it spreads the less useful it becomes

EFFICIENCY= (USEFUL ENERGY OUT/TOTAL ENERGY IN) X 100

EFFICIENCY= (USEFUL POWER OUT/TOTAL POWER IN) X 100

The energy flow in a system can be represented using Sankey diagrams 

(http://t2.gstatic.com/images?q=tbn:ANd9GcRfu7IyB6csuBIpQg7L4WDJUhJGTHPe12aKKL3xVLScNiLUXdDT)

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Heating and Insulating buildings

Solar panels can contain water heated by radiation from the Sun. The water can then be used to heat buildings or provide hot water.

There are a range of methods to reduce energy loss/consumption, these include:

  • Loft Insulation
  • Cavity Wall insulation
  • Double-glazed windows

These can be evaluated in terms of their payback time (time taken to recover up-front costs from savings)

U-values also help to measure the effectiveness of an insulator: The lower it is, the better the insulator

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