Physics topic 4

Energy
Energy is conserved. So its neither created or destroyed, it is converted from one form to the other. In any closed system the total energy remains the same. If we talk about energy lost, or wasted, we mean that it has escaped from the closed system.

• Thermal energy
• Light
• Electrical
• Sound
• Kinetic energy
• Chemical energy
• Nucleur energy
• Gravitational potential energy
• Elastic potentail energy

Sankey diagrams show the transfer of energy that takes place in a system. This is done by arrows and these are rougly proportion to the amount of energy they represent.
Total energy input= Total enery output

Efficiency= useful energy output from the system/total energy input from the system

If asked to give the efficiency in percentage you * 100

Conduction
Thermal conduction= is the transfer of thermal energy through a substance without the substance it self moving.

Thermal convection= is the transfer of heat energy through fluids (Liquids and gases) by the upward movement, less dense, regions in the fluid.

Radiation

Thermal radiation= is the trnasfer of heat energy in the form of infrared waves. It is the only method of heat transfer through a vacuum.

How to reduce the heat transfer by conduction:

• Use of vacuum
• Use of air
• Use of water

How to reduce heat transfer by convection:

• Use of vacuum
• Use trapped gas or liquid

How to reduce heat transfer by radiation:

• Use shiny surfaces

 Energy and work

Work= force * distance

Gravitational potential energy

GPE= mass*Gravitational field strength * height

Kinetic energy

KE=0.5*mv Squared.

Power

Power= work done/time taken

Energy resources and electricity generation
Hydroelectricity is a renewable form of energy that produces no greenhouse gases. The energy comes from the sun which evaporates water which then falls as rain in the mountains where it is then collected.
Tidal power and wave energy
Barrier across tidal estuaries can harness the kinetic energy of the sea, which drives water turbines as the tides come in. The water trapped behind the dam can then be used, as required, to drive the turbine once the tide goed out. These are renewable energy sources fo both tidal and wave power is the sun. The sun causes tidal movement, with the combination of wind it generates waves.
Wind power
This is done by using windmills which convert kinetic energy of the wind into other useful forms. Wind is a renewable sources that comes from the sun. This is because the sun produces the pressure vibrations in our athmosphere that drive the wind.
Solar power
This is a panel which converts light from the sun into electricty. This is a renewable source of energy that produces no carbon dioxide.

Advantages and disadvantages of choosing the form of generating electricity

• Cost this includes the setup of machinery and the cost of generating electricity.
• Renewable/non-renewables. Fossil fuels are finite so in the future alternatives must be found.
• Greenhouse gas emission. Buring fossil fuels produces carbon dioxide, which is a green house gas. Greenhouse gases trap heat in our athmosphere and contribute to global warming.
• Supply and demand. Some process cannot be turned on and off quickly and therefore cannot respond to demand and supply.
• Enviromental impact. Power stations can spoil views. Waste products can damage plants and animal life in the vicinity of power stations.
• Location. Factories can’t be close to the demand as their is no geographical locations there.