Physics 1

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  • Created by: Shamila
  • Created on: 13-12-12 17:44

Energy is measured in JOULES

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Energy is measured in JOULES

  • - When a substance is heated its particles gain energy.
  • - Gas or liquid - the particles move around faster
  • - Solid- Particles move around more rapidly
  • ENERGY IS MEASURED IN JOULES !!!
  • if there is difference in in temperature between two places then the energy will flow between them !!
  • Specific Heat Capacity
  • ENERGY=MASS x SHC x Temperature Change

Answer must be in                   JOULES                               

                                                                                                                                                           What is Specific Heat Capacity? is the amount of energy needed to raise the temperature of 1kg of a substance by 1 degreesC'  

                                                                                                                                              What is waters SHC ???      >>                                  4200                                                          

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Melting and Boiling !

When you heat like for example and ice cube ... heat ENERGY makes the PARTICLES vibrate FASTER. until the forces between them are overcome and the particles start to move around ... this is MELTING !

When a substance is melting or boiling your putting in energy !

THIS IS BREAKING INTERMOLECULAR BONDS !!

 they  are the flat spots on the graphs

Specific latent heat... is the energy needed to change STATE !   it is basically the amount of energy needed to melt 1kg of material withour changing its temperature ! (the material has got to be at its melting point already)

ENERGY= Mass X Specific Latent heat

By melting or Boiling you are BREAKING BONDS between particles !

 

 

 

 

 

 

 

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CONDUCTION !!!

Conduction occurs mainly in SOLIDS !    

In a solid the particles are quite close together so when one vibrates it causes another one to vibrate also !   HOWEVER some particles that vibrate faster than others pass on their EXTRA ...Kinetic energy ... to their Neighbouring Particles ... then they start to vibrate faster also... 

This process continues throughout the solid gradually the extra kinetic energy (heat) is SPREAD all the way THROUGH THE SOLID . 

THIS CAUSES A RISE IN TEMPERATURE ON THE OTHER SIDE. 

CONDUCTION OF HEAT is the process where VIBRATING PARTICLES pass on EXTRA KINETIC ENERGY to NEIGHBORING PARTICLES.

Metals are really good conductors of heat. LIQUIDS AND GASES conduct heat more slowly. !!THE PARTICLES ARENT HELD AS CLOSELY TOGETHER !! AIR is a good insulator ... !!                                                                   

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CONVECTION !!!

Convection occurs in LIQUIDS AND GASES

When you heat up a liquid or a gas then the particles move faster !... the fluid expands ... becoming less DENSE. And thennn... this warmer less dense fluid rises above its colder surroundings...... then... as this rises cooler fluid takes its place. and then... you end up with a CIRCULATION of fluid.... this is how IMMERSION HEATERS WORK !!!

CONVECTION occurs when the more energetic particles MOVE from the HOTTER region to the COOLER region and.... take their energy with them .. !!

RADIATORS... rely on convection for warm air to circulate the room .  

CONVETION CANNOT happen in SOLIDS. because the particles cant move only vibrate.

However to REDUCE CONVECTION you need to stop the fluid moving. foam insulation blocks pockets of air ... the air cant move so the heat has to conduct slower...

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Heat Radiation !!!

RADIATION is how we get HEAT from the sun. (heat transffered)...HEAT is radiated as INFRARED waves ...(They travel in STRAIGHT LINES ... at the speed of LIGHT)

REASONS radiation is different from conduction and convection... it can occur in a Vacuum , like SPACE ... this is the only way heat reaches us from the SUN ! ...It can ONLY occur through transparent substances, like air, glass and water.       

The amount of radiation emitted or absorbed by an object depends to a large extent on its surface colour and texture. HEAT radiation can only be ABSORBED OR EMITTED.

the hotter an object gets ..the more heat radiation it emits. cooler objects would absorb heat radiation emitted by hotter objects around them. MATTE BLACK surfaces are good absorbers and emitters of RADIATION.  LIGHT SHINY COLOURS ..REFLECT heat radiation

HEAT radiation is important in cooking. grills and toasters heat food by radiation...radiated by absorbed by the surface particles increasing KE... THEN CONVECTED AND CONDUCTED to more central parts. e.g...SHINY FOIL REFLECTING... over exposure to radiation damages body cells and causes burning.

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Comments

Shamila


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