Download PHYSICS 1A

PHYSICS 1A. REVISION.























Heat transfer
Heat moves from a warmer environment to a cooler one
Heat energy is transferred by conduction(solids), Convection ( liquids & Gases) and
Radiation ( Space & spaces between gas particles)
Conduction & convection involve particles but radiation does not
Light, shiny surfaces are poor absorbers and good emitters of heat radiation
The rate at which something radiates heat depends upon its surface to area ratio and
how much hotter it is than its surroundings
Heating a fluid will cause it to expand & become less dense, hence warm air/water rises
and cooling air/water sinks, because it contracts and becomes more dense ( convection
currents)
Insulators are poor conductors of heat.
Using energy
Energy cannot be created or destroyed, just transformed from one form to another
Not all energy transformation is useful, some energy is “wasted” ( usually as heat)
All energy eventually is transferred to the surroundings, which becomes warmer
Sankey diagrams are scale diagrams showing the energy transfers
Forms of energy-Electricity, Chemical, Kinetic, Potential (Gravitational & elastic), Sound,
Thermal (heat), Nuclear, Light. (Every Child Knows Pork sausages have no legs!)
Efficiency = Useful energy transferred (No unit or X 100 to give %)
Total energy supplied
Electrical energy
Power is the amount of energy transferred each second and measured in watts. Symbol W
Energy is measured in joules. Symbol J. ( 1 joule /second = 1 Watt)
Electricity is transferred around the country through the national grid. Step up
transformers increase the voltage ( this reduces power losses), step down transformers
reduce
Electricity sold in kilowatt-hours. kWh
To calculate cost of an appliance = Power (kW) X time used (hr) X Cost of unit
(Note 30 mins = 0.5h. 20 mins = 0. 33 h 15 min = 0.25h)
Generating electricity
In power stations water is heated to produce steam to drive turbines, these are
connected to a generator that produces electricity
Non- renewable fuels such as coal & gas produce most of Britain’s electricity.
Nuclear power stations use uranium and a process called NUCLEAR FISSION.
Renewable energy resources include – wind,waves,tides, falling water, sun, heat from
ground ( geothermal)
There are advantages & disadvantages to using renewable & non- renewable energy
sources. ( you must be able to recall these)
V Majer 2007