P7 Flashcards
What is chemical energy
Energy stored in the bonds of compounds
What is thermal energy
Energy relating to temperature, or a change in temperature
What is kinetic energy
Energy an object has due to motion
What is graviational energy
The energy an object has due to gravity
What is elastic energy
The mechanical potential energy of a material as work is performed on it
(Energy associated with deforming metals)
What is nuclear energy
Energy associated with nuclear fusion or fission
What is electrostatic energy
Energy associated with the distortion of electric fields and charges
What i magnetic energy
Energy associated with the separation or joining if magnetic poles
What is non-zero speed
The speed of any object with kinetic energy
How is GPE calculated
Mass × gravity × height
How is kinetic energy calculated
1/2mv²
How is thermal energy calculated
Mass × SHC × ∆temp
SHC is the energy needed to increase an object by 1°C or 1K
How is elastic energy calculated
1/2kx²
K= spring constant
X = extension
How is energy transferred
Mechanically → using forces
Electrically → using current
Heating by particles
Heating by radiation
.
In what way is kinetic energy transferred
Mechanically
How is efficiency of energy transferr calculated
(useful output ÷ output energy)×100
(Useful output ÷ input)×100
How are thermal and chemical energy transferred
By heating of particles
Chemical energy can also be transferred mechanically
How do electromagnetic waves transfer energy
Heating by radiation
The greater their frequency, the greater their energy transfer
Describe the changes in energy when falling down a steep slope
Gravitational energy is transferred mechanically to kinetic energy
Then mechanical again kinetic energy is transferred to chemical energy
What is the conservation of energy
Energy cannot be created or destroyed
Energy can only be transferred between stores
What happens during the transfer of energy in a closed system
The increase of energy in one store will be equal to the decrease in another store
Where does an electric current transfer energy from
From a chemical store in a battery
From a chemical or nuclear store, used to power the mains elesctricity
What are power ratings
Ratings given to appliances to show how much energy they will transfer faster
Whats an advantage to using high energy rated appliances
They will complete a task faster, but at a higher price
How do you calculate electrical work done
Work done = power × time
What is electrical work done measured in
kWh (killowatt hour)
How do you transfer joules to kWh
1kWh = 3.6×10⁶ J
1kW = 1000J
Hour = 3600s
How do you calculate the cost of an appliance
Electrical work done × current rate
What do electrical appliances do (energy transfer)
Transfer energy electrically from chemical stores
How is energy transferred when current flows through a wire
When current flows through a wire the wire heats up
This means energy is transferred to a chemical store and is wasted
Why cant appliances such as motors be 100% efficient
As energy is transferred to the thermal store
In what systems is chemical energy lost to the surroundings
In all mechanical systems
Why is electricity transferred at a high voltage but low current
To reduce the heat loss to the environment
(Through heating of particles)
What is energy diserpation
Loss of energy to the surroundings
How is energy loss reduced in mechanical systems
Using lubrication reduces friction, and therefore energy loss is reduced
How is heat loss by heating of particles reduced
By using insulation
(Insulating materials)
What is thermal conductivity
A measure of how quickly energy is transferred through a material
The thermal conductivity of a material is fixed and doesnt change based on its mass
The higher the thermal conductivity the faster energy is transferred
Why are houses built using materials with a low thermal condictivity
Prevents hot air entering and making the house hot during summer
Prevents hot air leaving the house during winter
It reduces the transfer of heat to the surroundings
What is a cavity wall
A method of insulating a building
Insulating material (low thermal conductivity) is placed between the inner and outer walls of a house
How does loft insulation help reduce heat loss
As hot air rises it is important to have good loft insulation
This will reduce the heat loss to the surroundings
How does double glazing reduced a houses thermal conductivity
As that is placed between the panes of glass has a low thermal conductivity
Glass also has a relatively low thermal conductivity
How does increasing the thickness of a wall affect energy transfer
The thicker the wall the slower the transfer of energy
Heat is transferred by conduction at a slower rate
There is a greater distance the energy has to be moved
What is conduction
Energy transferred between neighbouring atoms or molecules
Why are igloos warm
Although ice is a ‘cold’ material, they have a low thermal conductivity, and therefore can trap heat inside
How do you calculate the efficiency of energy transfer
Efficiency = (useful output energy ÷ input energy) × 100
What is a sankey diagram
A diagram drawn showing total energy, and how much is wasted or useful
The size of an arrow represents the amount of energy transferred
How are sankey diagrams drawn
You need to use a scale so that the size of the arrow is proportional to the energy
How do you improve efficiency
Use insulation.
Use materials that reduce unwanted energy transfer
Use technology to produce better devices, e.g LEDs which give of little heat
