4b) Energy transfer

Energy conservation:

1. Energy conservation ---> using fewer resources because it might run out 
2. Principle of the conversion of energy ---> energy can never be created nor destroyed, it can only be transferred from one to another

EFFICIENCY = (Useful Energy Output/ Total Energy Input) x 100

No device is 100% efficient and wasted energy is always dissipated as heat

Sankey Diagrams:

show the amounts of energy changed from one form to another 

10/100 x 100= 10% efficient 

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Heat Transfer 

• tends to flow away from a hotter object to its cooler surroundings 
• can be transferred by radiation, conduction or convection

Conduction:  

• Heat energy is passed from particle to particle through collisions 
• Metals are good conductors because heat energy is also transferred by free electrons 

Convection:

• occurs when the more energetic particals MOVE from the HOTTER REGION to the COOLER REGION- and take their heat energy with them.Examples: kettles, hot water tanks and convector heaters
• Hot fluids are less dense and so they rise transferring heat energy 
• Immersion heater example:
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Radiation:

• All objects are continually emitting and absorbing heat radiation
• An object that's HOTTER than its surroundings EMITS MORE RADIATIONS than it ABSORBS (as it COOLS down) 
• An object that's COOLER than its surroundings ABSORBS MORE RADIATION than it EMITS (as it WARMS UP) 
• works through a vacuum

Insulation ----> designed to prevent heat transfer- trapped air is a very good insulator