CP3 Conservation of Energy Flashcards
What is mass measured in?
Kilograms (Kg)
What is energy measured in?
Joules ( J )
Conservation of Energy
Energy can not be created or destroyed; Energy can only be transferred from one store to another.
What is Energy Efficiency?
A way of describing how good a device is at transferring energy into useful forms.
What’s the equation for energy efficiency?
Efficiency = useful energy transferred / total energy
Name two things that affect the rate of energy transfer.
- Thickness of material
- Temperature difference
Thermal Conductivity
A measure of how well a material conducts energy when it is heated
What does a high thermal conductivity mean?
The material is good at conducting thermal energy
What is the equation for Kinetic Energy?
KE = 0.5mv^2
Kinetic Energy = 0.5 * Mass * Velocity^2
What is Kinetic Energy measured in?
Joules
Convert 250g into Kg
250g = 0.25kg
250 / 1000 = 0.25
What kind of diagram do we use to show energy transfers?
Sankey Diagram
What is a ‘System’ when we talk about energy transfers?
A set of things being studied - for example a kettle, the water in it, and it’s surroundings form a simple system.
An object or a group of objects that interact.
Dissipated
Spread out
Conduction
The way energy is transferred through solids by heating.
Vibrations are passed from particle to particle.
Convection
The movement of particles in a fluid depending on their temperature.
Hotter, less dense regions rise, and cooler, denser regions sink.
Emit
To give out
What does it mean if an energy source is non-renewable?
It will eventually run out because we cannot renew our supplies of it.
What does is mean if an energy source if renewable?
It will never run out
Name all 8 energy stores
- Magnetic
- Thermal
- Elastic potential
- Gravitational potential
- Nuclear
- Electrostatic
- Chemical
- Kinetic
Define Thermal Energy Store and give an example
The energy a system has because of its temperature.
An example could be that the thermal store of water in a kettle increases when you turn the kettle on.
Define Kinetic Energy Store and give an example of one
The energy a system has because it’s moving.
An example could be that if a car speeds up from 30km/h to 60km/h then its kinetic energy store will increase.
Define Gravitational Potential Energy Store and give an example of one
The energy a system has because of how high it is above the ground.
An example could be: if you pick up an object off the ground, its gravitational potential will increase.
Define Chemical Energy Store and give an example
The energy stored in chemicals including food, fuels, and batteries.
An example could be: If you turn on a battery powered torch, the chemical energy stored in the battery will decrease.
Define Elastic Potential Energy Store and give an example
The energy stored in a system when it is stretched or squashed.
Example: A spring that is stretched will have an increased elastic potential store.
Define Magnetic Energy Store and give an example
The energy stored when two repelling magnetic poles have been pushed together or two attracting poles have been pulled apart.
Example: If you hold two magnets with opposite poles together, they will attract each other. If you pull them apart then you will have increased the magnetic energy store.
Define Electrostatic Energy Store and give an example
The energy stored the repelling charges have been moved closer together or attracting charged have been pulled apart.
Example: If you touch a Van de Graaff generator, then your hair will stick up because the hairs will have a positive charge and repel each other.
Define Nuclear Energy Store and give an example
The energy stored in the nucleus of an atom
Example: the huge amount of energy stored in the nuclei of atoms is why nuclear weapons are so devastating.
How does energy move from one store to another?
Through an energy transfer pathway
Name the 6 Energy Transfer pathways
- Mechanical (forces)
- Electrical
- Heating
- Radiation (waves)
- Light
- Sound
What energy is stored in a chocolate bar?
Chemical
What type of energy would you find in a train moving at 70km/h ?
Kinetic Energy
What energy is stored in a rocket during take off?
Kinetic Energy and Gravitational Potential Energy
What type of energy is found in the nucleus of an atom?
Nuclear Energy
What happens to wasted energy?
It is dissipated to the surroundings
For every 100J of energy put into a lightbulb, 5J is useful.
Calculate the efficiency of the light bulb.
0.05
5J / 100J = 0.05
A device transfers 30J of useful energy every second. The total energy transferred to the device each second is 50J.
Calculate its efficiency.
0.6
30J / 50J = 0.6
A light bulb transfers 90J of energy by heating every second. 100J of energy is transferred to the light bulb every second by electricity.
Calculate its efficiency.
0.9
90J / 100J = 0.9
What number can the efficiency of a device never be greater than?
1 (or 100%)
What 3 ways can energy be transferred by heating?
- Conduction
- Convection
- Radiation
