Physic - Energy

Physic - Energy

1. Heat

   • Heat is transferred in 3 different ways
     • Radiation
       • Can be emitted by solids, liquids and gases
       • The bigger the temperature difference between the body and its surroundings the faster the energy is transferred
       • The hotter the object the more it radiates
       • Dark, matt surfaces absorb infrared radiation best
         • Light, shiny things reflect infrared radiation
           • Flasks - have silver inner surfaces to keep the radiation from falling out
         • Solar hot water panels uses matt black surfaces
           • They heat the pipes underneath to produce hot water
     • Conduction
       • Main form of heat transfer for solids
         • Because the particles are close together
           • Collide more often - passing energy
           • Faster in denser solids
         • The heat moves from one part of a solid to another
       • VIBRATING PARTICLES PASS ON THEIR KINETIC ENERGY TO NEIGHBOURING PARTICLES
       • It doesn't mean they are hotter, just metals conduct quicker
     • Convection
       • Transferred energy through particales
       • Main form of heat transfer for liquid and gases
       • ENERGETIC PARTICLES MOVE FROM HOTTER REGION TO THE COOLER REGION AND TAKE HEAT WITH THEM.
       • Can't happen in solids because the particles don't move enough
       • Hot water rises and cool water sinks
       • Convection currents is the most efficient in roundish containers
       • CONVECTION CURRENTS ARE A CHANGE IN DENSITY
       • A radiator works on convection currents also
   • Heat radiation
     • Heat radiation is the transfer of heat by infrared radiation (IR)
   • Rate of heat transfer
     • Heat is radiated from the surface of an object
       • Larger the surfaces area the more infrared waves can be emitted so the quicker the transfer of heat
     • Factors such as the material effect it also
     • If they are a good conductor or not- moves heat away
     • Objects designed to limit heat transfer
       • Flasks are designed to stop heat transfer
         • Vacuum walls to stop conduction and convection
         • Silver- to keep radiation loss at a minimum

2. Condensation and Evaporation

   • Condensation
     • Gas is turned to liquid
       • When a gas cools the particles slow down
         • Attractive forces pull them together
           • Close enough together turn to liquid
             • Can happen when comes into contact with cold surfaces
   • Evaporation
     • When liquid turns to gas
       • Particles escape form liquid
         • Near the surfaces
           • With enough kinetic energy
             • Then the left over liquid has less kinetic energy
               • Temperature falls - liquid cools
   • Rate of EVAPORATION
     • TEMPERATURE is higher
     • DENSITY is lower
     • SURFACES AREA is larger
     • AIRFLOW of the liquid is greater
   • Rate of CONDENSATION
     • TEMPERATURE OF THE GAS is lower
     • TEMPERATURE OF THE SURFACES AREA THE GAS TOUCHES is lower
     • DENSITY is higher
     • AIRFLOW IS LESS

3. Energy efficiency in the house

   • PAYBACK TIME = INITIAL COST / ANNUAL SAVING
   • The most effective are the ones with the larges annual saving
   • The most cost effective tend to be the cheapest
     • Short pay back time
   • What can be done?
     • CAVITY WALL INSULATION
       • Foam squirted into the gap between the bricks
         • Reduces CONVECTION + RADIATION across the gap
     • LOFT INSULATION
     • DRAUGHT PROFFING
       • Strips of foam and plastic around the door
         • Stops CONDUCTION and CONVECTION
     • HOT WATER TANK JECKET
       • Similar to flask, vacuum on the outside
       • Reduces CONDUCTION AND RADIATION
     • THICK CURTAINS
       • Big bits of cloth over the windows
         • Reduces CONDUCTION and RADIATION
   • MEASURE IN UV
     • The lower the UV levels the slower heat loss is

4. Specific heat capacity

   • TELLS YOU HOW MUCH ENERGY SOMETHING CAN STORE
     • For example; you need 4000j to warm up 1 kg of water by 1°C
   • Heaters
     • Heaters have high SHC so they can store large amounts of heat energy
     • Water has high SHC so good for heating in pipes
   • Of oil = 2000J/°C
   • Of water= 4200 J/°C

5. Energy transfer

   • Types of energy
     • ELECTRICAL ENERGY
       • Current flows
     • LIGHT ENERGY
       • From the light, sun ETC.
     • SOUND ENERGY
       • From anything noisy
     • KINETIC ENERGY
       • Anything that moves
     • NUCLEAR ENERGY
       • Released only from nuclear reactors
     • HEAT ENERGY
       • Flows from hot objects to cold objects
     • GRAVAIATIONAL POTENTIAL ENERGY
       • Processed by anything that can fall
       • Stored energy
     • ELASTIC POTENTIAL ENERGY
       • Stretched springs, elastic ETC.
       • Stored energy
     • CHEMICAL ENERGY
       • Processed by foods, fuels, batteries ETC.
       • Stored energy
   • ENERGY IS NEVER CREATED OR DESTROYED
     • CAN BE TRANSFERRED, STORED OR DISSIPATED

6. Machines and Electrical appliances

   • Losses
     • Useful devices can transform energy form one form to another
     • In the process there will always be energy loss
       • Often as heat
     • The less wasted the more efficient
   • Formula
     • EFFICIENCY=USEFUL ENERGY OUT/ TOTAL ENERGY IN
   • Useful energy
     • The energy ends up as heat and dissipates to other forms
   • How to know what to choose?
     • The costs may be higher at the beginning however, they end up being cheaper
     • Think of the practical advantages
     • Example comparison
       • Clockwork Radios + Battery Radios
         • Powering a clockwork radio is elastic potential energy which is free
           • Sometimes tedious
           • Better for the environment
         • Batteries cost money
           • Easy
           • Not so good for the environment
   • Could 'waste' energy be useful ?
     • Heat exchangers reduce the amount of heat energy lost
       • Pumping cold fluid through the escaping heat
         • The temperature of the liquid rises and gains heat energy
           • Then can be converted into a form that is useful again
   • Standard of living
     • Poor countries cant access electricity
     • Refrigerators can help store food safely
       • And store vaccines
       • Hospitals rely on electricity
         • Without a reduction in life expectancy
     • Electricity can also effect communications

7. Energy transformation graph

   • SANKEY DIAGRAMS
     • The thickness of the line represents the amount of energy
     • Tells you the energy used and wasted visually
     • 100J in
     • 80J lost in HEAT ENERGY
     • 20J useful KINETIC ENERGY
     • To do it precisely you can measure the small squares

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