(1) Conservation and Dissipation of Energy Flashcards
Define the law of energy conservation
Energy cannot be created or destroyed only transferred/ dissipated into the surroundings
(So the energy is a system does not change)
What is waste energy?
Energy that is not used by the device for it desired purpose
What are the useful and wasted energy outputs of an electric fan heater?
Useful= warms the air and surrounding objects (thermal energy)
Wasted= the moving components make noise (sound energy)
Describe the energy changes that occur in a filament light bulb
Electrical energy is transferred into light and thermal energy
(light is useful and thermal energy is wasted)
Equation for Efficiency
Efficiency= useful energy output/ total energy input
Efficiency= useful power output/ total power output
(Efficiency is normally a % so x100)
- it is never more than 100
How can efficiency of a system be increased?
Reducing waste output:
1. Reduce friction by lubrication
2. Reduce heat loss by insolation
3. Reduce sound from machinery by tightening loose parts etc
4. Reduce air resistance by using streamlined shapes
Describe the energy transfer of a material with a high thermal conductivity
Rate of energy transfer through the material is higher with a higher thermal conductivity
State 3 methods to reduce heat loss in a building
- Double glazing
- Thicker walls
- Loft and wall insolation
Do double glazed windows have a higher or lower thermal conductivity than single glazed windows?
Lower meaning less energy transfers through them
What factors affect the rate of cooling of a building?
Thermal conductivity of the walls
(Thicker walls)
How can the efficiency of a mechanical machine with moving parts be improved?
-lubricate to reduce friction
-cut out noise by tightening loose parts
How could you improve the efficiency of a boiling pan of water?
-placing a lid on the pan reduces heat loss
