Topic 3 - conservation of energy Flashcards
Explain what it is meant by conservation of energy
the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time.
Explain how to draw and interpret diagrams to represent energy transfer
In all flow diagrams there must be energy stores and energy transfers present to show how energy is transferred from one store to others.
Based on the law of conservation of energy, the total energy present in the original stores must be equal to the energy present is the stores after the transfers have taken place, since you can’t destroy or create energy in any give system.
To draw them, draw boxes with the use and arrows suggesting how its transferred (eg mechanical) and spilt them into their stores
Explain the four different ways of energy transfer
MECHANICALLY - by a force moving through a distance
ELECTRICALLY - by the use of electric current
THERMALLY - because of a difference in temperature
RADIATION - by waves such as electromagnetic or sounds
Some of the energy will be usefully transferred, and some will be wasted or DISSIPATED
Explain how and why mechanical processes become wasteful
Mechanical processes become wasteful when they lead to a rise in the temperature in the surroundings through heating. In all system changes, energy is stored in less useful ways.
Eg
The light and sound energy from a TV will eventually be absorbed by walls and by people leading to a rise in temperature
Explain what happens when there is an energy transfer in a closed system
When there are energy transfers in a closed system, there is no net change to the total energy in the system
Explain the eight main energy stores and give examples
CHEMICAL - batteries, food, fuel KINETIC - moving objects GRAVITATIONAL POTENTIAL - raised mass ELASTIC - stretched spring THERMAL - hot object MAGNETIC - two magnets ELECTROSTATIC - two charges NUCLEAR - radioactive decay
Give an example of where energy is wasted (dissipated)
Camping gas + oxygen (chemical store) goes to useful store as hot water in pan by heating but also goes to pan and surrounding air thermal store by heating as wasted energy
Explain ways of reducing unwanted energy transfer
Unwanted energy transfers can be reduced through lubrication and thermal insulation
Explain the factors that determine the rate at which thermal energy is transferred through the wall of a house
1) the difference in temperature between the warmer interior and colder exterior
2) the thickness of the walls
3) the material that the walls are made from
Describe the effects of the thickness and thermal conductivity of the walls of a building on its rate of cooling qualitatively
A material with a better thermal conductivity is a better conductor of energy than one with a lower thermal conductivity. The rate they transfer energy differs due to different materials having different relative thermal conductivities. Lower thermal conductivity results in higher temperatures.
Thickness also reduces or increases the rate at which the wall transfers energy. Thicker walls result in less energy transferred, resulting in higher temperatures.
Explain what efficiency is
All machines waste some of the energy they transfer, most machines waste energy as heat energy. The efficiency of a machine is a way of saying how good it is at transferring energy into useful forms . The higher the efficiency, the better the machine is at transferring energy into useful forms.
Explain how efficiency can be increased
This can be achieved by reducing wasted energy transfers so more of the input energy is usefully transferred.
Mechanical devices can be made more efficient through lubrication to reduce the friction between moving parts of a machine and increase the amount of useful energy transferred.
For systems that are designed to transfer thermal energy, the efficiency can be improved by reducing the wasteful dissipation of thermal energy to the surroundings, for example by using insulation.
Explain the renewable energy resources on earth
- BIO FUELS - animal or plant matter used to generate electrical energy, thermal energy or used to power cars
- HYDROELECTRICITY- generates electricity from water flowing behind a dam flowing down a pipe and turning a turbine to generate electricity
- WIND TURBINES - use kinetic energy from the wind to generate electricity
- TIDAL POWER - uses the rise and fall of the tide or tidal currents to generate electricity
- SOLAR CELLS - convert solar energy Or energy directly from the sun , directly to electricity. Solar energy can be used directly to cook food or to heat water
Explain the non renewable resources used
- Nuclear fuels such as uranium are used to generate electricity and are used as energy sources in spacecraft
- Fossil fuels are coal, oil and natural gas. They are used to generate electricity, to power transport, and to heat homes and for cooking
- They are available all the time, unlike some renewable energy sources
Explain patterns and trends in the use of energy resources and factors affecting demand for energy
The use of energy resources has changed over the years, this is because of several factors:
- The worlds population - in the past 200 years, the population of the world has risen from 1 billion to 7 billion people
- The development of technology - vehicles and other devices have increased in use and these require energy
- Electrical energy - power stations require fuel to generate electricity
- most of the worlds energy use has been fossil fuels, before about 1900 wood was rte main source of fuel and its use has remained constant over time.
- in most recent years, there has been an increase in the use of nuclear fuel and hydroelectric power
