Topic 1 - Energy Flashcards
What is specific heat capacity?
Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1•C
Different materials and specific heat capacity
- Diff. Materials have diff specific heat capacities
- More energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others
What is SHC a measure of?
The measure of how much energy a substance can store
What is efficiency?
- Some of the input energy is usually wasted by being transferred to a useless energy store - usually a thermal energy store
- The less energy wasted in this energy store, the more efficient the device is
How to improve the efficiency of energy transfers:
- Insulating objects
- Lubricating objects
- Making objects more streamlined
How to calculate the efficiency of energy transfers
Efficiency = Useful output energy transfer / total input energy transfer
How to calculate the efficiency of power transfers:
Efficiency = useful output power / total input power
Useful energy input and total energy output
Not always equal
Devices and efficiency.
- NO device is 100% efficient
- Wasted energy usually transferred to useless thermal energy stores
Electric heaters and efficiency
- An exception
- They’re usually 100% efficient because all the energy in the electrostatic energy store is transferred to ‘useful’ thermal energy stores
Electric drills and efficiency
- It’s energy is transferred to lots of diff energy stores, but quickly ends up in all thermal energy stores
- Ultimately, all energy ends up transferred to thermal energy stores
8 energy stores
- Thermal energy stores
- Kinetic energy stores
- Gravitational potential energy stores
- Elastic potential energy stores
- Chemical energy stores
- Magnetic energy stores
- Electrostatic energy stores
- Nuclear energy stores
System
A single object (e.g. the air in a piston) or a group of objects (two colliding vehicles)
Closed system definition
Systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero
4 main ways energy is transferred
- Mechanically (by a force doing work)
- Electrically (work done by a moving charges)
- By heating
- by radiation (e.g. light or sound)
Wind power
- Lots of little turbines in exposed places
- Each turbine has a generator inside, rotating blade turn the generator and produce electricity
Advantages of wind turbines
- No pollution - apart for a bit when they’re manufactured
- No fuel costs and minimal running costs
- No permanent damage to landscape - can be removed
Disadvantages of wind turbines
- They spoil the view
- Can be v noisy, annoying for people living nearby
- Turbines can stop when wind stops, what if winds also too strong?
- Impossible to increase supply when there’s extra demand
- Initial costs quite high
Solar power
- Solar cells generate electric currents directly from sunlight
- Usually used to generate electricity on a relatively small scale
Advantages of solar power
- No pollution (although factories use quite a lot of energy and produce some pollution when manufacturing the cells)
- In sunny countries its a v reliable source of energy in daytime
- Can still be cost effective in cloudy country’s like Britain
- Energy is free and running costs almost nil
Disadvantages of solar power
- You can’t increase the power output when there’s extra demand
- Initial costs are high
Where is solar power usually used
- Often best sources of energy to charge batteries in calculators and watches (don’t use much electricity)
- Powers electric road signs and satellites
- Used in remote places where there’s not much choice (e.g. the Australian Outback)
Geothermal power
Uses energy from underground thermal energy stores to generate electricity or to heat buildings directly
Advantages of geothermal power
- Brilliant free energy that’s reliable w/ v few environmental problems
