Physics GCSE Part 1A

THERMAL RADIATION

Key points:

• Thermal radiation is the transfer of energy by infra-red waves. These waves are part of the electromagnetic spectrum.
• All objects emit thermal radiation
• The hotter an object is the more thermal radiation it emits 

Key words: thermal, heat, radiation, infra-red, emit

SURFACES AND RADIATION

Key points:

• Dark, Matt surfaces are better emitters of thermal radiation
• Dark matt surfaces are better absorbers of thermal radiation

Key words: absorber, emitter

examiner hint: exam questions often involve different applications of absorption and emission

CONDUCTION

Key Points:

• Conduction in a metal is due mainly to free electrons transferring energy inside the metal
• Non-metals are poor conductors because they do not have free electrons
• Materials such as fibreglass are good insulators because they contain pockets of trapped air

Key words: conduction, conductor, insulator

examiner hint: Know some examples of insulators and how they are used 

CONVECTION

Key points:

• Convection takes place only in liquids and gases (fluids)
• Heating a liquid or a gas makes it less dense
• Convection is due to hot liquid or gas rising

Key words: fluid, convection, convection current

Examiner tips: -

• remember the type of surface makes no difference to the amount of conduction or convection from an object - it only affects radiated heat energy.
• Make sure you can explain how convection currents are set up in terms of a fluid's change in density

HEAT TRANSFER BY DESIGN

Key points:-

• A radiator has a large surface area so it can lose heat easily
• Small objects lose heat more easily than large objects
• Heat loss from a building can be reduced by :-
  • aluminium foil behind radiators
  • cavity wall insulation
  • double glazing
  • loft insulation

Key words:- maximise, minimise

HEAT TRANSFER BY DESIGN (cont)

Examiners tips :-

• A vacuum flask is an application that often comes up in exam questions. Make sure you can relate to the structure of the vacuum flask to conduction, convection and radiation. A vacuum flask keeps heat in so that hot  things stay hot. It also keeps heat out so that cold things stay cold.
• To reduce heat loss in a particular situation remember to include heat losses by conduction, convection and radiation

FORMS OF ENERGY

Key points:-

• Energy exists in different forms : - Light, Thermal (heat), sound, kinetic (movement), Nuclear, Electrical, Gravitational Potential, Elastic Potential (or strain), Chemical
• Gravitational Potential, Elastic Potential and Chemical are all forms of stored energy.
• Energy can transform from one form to another form

Key words: - energy, kinetic, potential, stored

Examiners tips:- make sure you are familair with the different forms of energy and know some examples of each of them

CONSERVATION OF ENERGY

Key points:-

• Energy can be transformed from one form to another or from one place to another
• Energy cannot be created or destroyed

Key words:- transform, transfer, conservation

Examiners tips:-

• Remember that the conservation of energy applies in any situation
• Know some forms of energy transformations
• The conservation of energy is an extremely important idea in Physics so it often comes up in examination questions

USEFUL ENERGY

Key Points:-

• Useful Energy is energy in the place we want it and in the form we need it
• Wasted energy is energy that is not useful energy
• Useful energy and wasted energy both end up being transferred to the surroundings which become warmer
• As energy spreads out, it gets more and more difficult to use for further energy transfers

Key words:- device, input energy, useful energy, wasted energy

Examiners tips :- Remember that energy cannot be destroyed - it is better to talk about energy that is wasted than to say energy is lost.

ENERGY AND EFFICIENCY

Key points:-

• Energy is measured in joules
• The efficiency of a device = the useful energy transferred divided by the total energy  supplied to the device
• wasted energy causes inefficiency

Key words:- joule, efficiency

Examiners tips:-

• No device can be 100% efficient (except an electric heater). If the answer in an efficiency calculation is greater than 1 or 100% it is wrong
• Efficiency is a ratio - it does not have a unit
• When you have to substitute energies into an efficiency equation you may be given the energy usefully transferred or you may be given the energy wasted and have to subtract this from the total energy to find the useful energy transferred.

ELECTRICAL DEVICES

Key points:-

• Electrical energy is energy transfer due to an electrical current
• Uses of electrical devices include :- Heating, lighting, making objects move (using an electric motor) creating sound and visual images

Key words:- electrical energy, electrical devices

Examiners tips:- Remember that  all electrical devices will transform some electrical energy to heat, but this may not be useful energy transformation.

ELECTRICAL POWER

Key points:-

• The unit of power is the Watt (W) equal to 1 joule per second
• 1 kilowatt = 1000 watts
• 1 watt = 0.001 kilowatts
• power (in watts) = energy transferred (in joules) divided by time taken (in seconds)

Key words:-  Power, watt, kilowatt

Examiners tips:-

• Make sure you can convert between watts to kilowatts and between joules to kilojoules
• The more powerful a device the greater the rate at which it transforms energy

USING ELECTRICAL ENERGY

Key points:-

• Energy transferred (kWh) = power of device (Kw) * time(h)
• Total cost of electricity = number of kWh * cost per kWh

Key words:- kilowatt-hour, kilowatt, hour

Examiners tips:-

• Take care with the units here - they are tricky! Remember that the kilowatt hour is a unit of energy, not power.

THE NATIONAL GRID

Key points:-

• The National Grid is a network of cables and transformers
• We use step-up transformers to step power stations voltages up to the grid voltage
• We use step-down transformers  to step the grid voltage down for use in our homes.
• A high grid voltage reduces energy loss and makes the system more efficient

Key words:- National Grid, step-up transformer, step-down transformer

Examiners tips:-

• Be able to describe the reasons why voltages are increased and decreased within the national grid system
• Know the different parts of the National Grid System and the order in which they are used :- Power station (25kv), step-up transformer, the grid (132kv), step-down transformer, underground mains cable to homes (230v)

FUEL FOR ELECTRICITY

Key Points:-

• Electricity generators in power stations are driven by turbines
• Much more energy is released per kilogram from Uranium than from fossil fuels

Key words:- turbine, generator, fossil fuel, fission

Examiners tips:- Most power stations burn fuel to produce heat. In a nuclear power station uranium is not burned - the heat comes from the process of nuclear fission

ENERGY FROM WIND AND WATER

Key points:-

• A wind turbine is an electricity generator on top of a tall tower
• A wave generator  is a floating generator turned by the waves
• Hydro-electricity generators are turned by water running downhill
• A tidal power station  traps each high tide and uses it to turn generators

Key words:- wind, waves, hydro-electricity, tides, estuaries

Examiners tips :-

• There are a number of ways electricity can be generated from water. Exam questions can be asked about any of them so learn them all carefully and make sure you know the differences between them

POWER FROM THE SUN AND THE EARTH

Key points:-

• We can convert solar energy into electricity using solar cells or use it to heat water directly in solar heating panels.
• Geothermal energy  comes from energy released by radioactive substances deep inside the earth

Key words:- solar energy, solar cells, solar heating panels, geothermal energy

Examiners tips:- Adding the details in a description of Geothermal energy will get you extra marks

ENERGY AND THE ENVIRONMENT

Key points :-

• Fossil fuels produce greenhouse gases
• Nuclear fuels produce radioactive waste
• Renewable energy resources can affect plant and animal life

Key words:- renewable, non-renewable, polluting

Examiners tips :-

• If you are asked to discuss energy resources, remember that they all have advantages and disadvantages - you must include both.

WORKING OUT QUESTIONS WITH EQUATIONS

• Look for what the question asks for in the answer
• Find the equation that contains this
• Substitute all the information you have (IN THE CORRECT UNITS)
• Arrange the equation to get the answer to the missing detail
• Calculate the answer
• Check everything is in the correct units
• Check you have included units in your answer

Know the 5 equations :-

• Energy Efficiency
• Energy supplied
• Power
• Energy transferred
• Total Cost

ENERGY EFFICENCY =

                 Useful energy transferred by the device

                    Total energy  supplied to the device

ENERGY SUPPLIED =

              Useful energy delivered plus wasted energy

POWER IN WATTS =

                             energy transferred in watts

                               time taken in seconds

1 KILOWATT = 1000 Watts

1 WATT = 0.001 Kilowatts

ENERGY TRANSFERRED IN KILOWATT HOURS (kWh) =

                          Power of device in KW * time taken in hours

TOTAL COST =

                          Number of kWh * cost per KWh