gcsephysics

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Revising for air resistance is such a drag

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Because I am absolutely useless at explaining distance-time and velocity-time graphs without physically (ha, get it: Physically! Hahahahah— never mind) having to make a video, here’s a video courtesy of BBC Bitesize to cover the main points discussed in previous posts… although I promise I will make my own post on the matter when I can be bothered to get my camera and pencils out…

That aside, this is a pretty good video, and isn’t very long (making it ideal for short bursts of revision), so give it a shot, and have a nice day! :D

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Wave Power

as waves come into the shore, they provide an up and down motion which can be used to drive a generator

lots of wave powered turbines need to be located around the coast for it to generate a substantial amount of energy

there's no pollution, however they can be a hazard to boats and spoil the view

wave turbines are fairly unreliable as waves tend to die out when the wind drops

initial costs are high, but there are no fuel costs and minimal running costs

wave power is not good to provide energy on a large scale but can be very useful on small islands

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Hydroelectric Power

hydroelectric power usually requires the flooding of a valley by building a big dam

rainwater is caught and let out through turbines

there is no pollution but there is a big impact on the the environment due to the flooding of the valley - rotting vegetation releases CO2 and methane and some species can lose their habitats

a big advantage is it can provide an immediate response to an increased demand for electricity

always reliable - except in times of drought

initial costs are high but no fuel's required and running costs are low

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Solar Power

solar cells generate electric currents directly from sunlight

they're often used in remote places such as the Australian Outback 

they create no pollution, but use quite a bit of energy to manufacture in the first place

in sunny countries solar cells are a reliable source of energy, and can still be cost effective in cloudy countries - but only in the daytime

initial costs are high but after that energy is free and running costs are minimal

usually not practical or too expensive to connect them to the national grid - they're better used on a small scale

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Wind Power

wind turbines are located in exposed places like on moors or round coasts

each turbine has it's own generator inside it so electricity is generated directly from the wind turning the blades, which turn the generator

there's no pollution (other than manufacturing)

some people say they spoil the view

1500 wind turbines are required to generate the same amount of energy as one coal-fired power station, and these take up a lot of space and change the scenery

they can be very noisy, which is annoying for nearby residents

wind turbines are dependent on the weather- when there's no wind, no power is generated

the initial costs are quite high, but there are no fuel costs and minimal running costs

they create no permanent damage to the environment

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Power Stations

the fossil fuel is burned to convert stored chemical energy into heat (thermal energy)

the thermal energy is then used to heat water to produce steam

the steam turns a turbine, converting heat into kinetic energy

the turbine is connected to a generator, which transfers kinetic energy into electrical energy

voltage is increased by a step-up transformer for efficient transmission, then the electricity is distributed to homes via the national grid

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Energy Sources

non renewable energy resources will run out one day and they all do damage to the environment but currently provide most of our electricity

coal

oil

natural gas

nuclear fuels (uranium and plutonium)

renewable energy resources will never run out, most of them still do damage the environment, but in less nasty ways than non-renewable, however they don't provide a lot of energy and are often unreliable because they depend on the weather

wind

waves

tides

hydroelectric

solar

geothermal

food

biofuels

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The Cost of Electricity

the amount of energy transferred by an appliance depends on its power and the amount of time the appliance is switched on

power is usually measured in watts (W) or kilowatts (kW)

energy is usually measured in joules (J) but the standard units of electrical energy are kilowatt-hours

a kilowatt-hour is the amount of electrical energy used by a 1 kW appliance left on for 1 hour

ENERGY = POWER x TIME

No. of UNITS (kWh) used = POWER (kW) x TIME (hours)

and to find the cost:

COST = No. of UNITS (kWh) x PRICE per UNIT

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Heat radiation.

*puts finger on butt*

TSSSSS

More notes

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Sankey Diagrams

sankey diagrams, or energy transformation diagrams, are a visual representation to how much energy put into a machine is being used usefully and how much is being wasted

the thicker the arrow, the more energy it represents

you can use these to calculate the efficiency

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Efficiency of Machines

a machine is a device that transforms energy from one form to another

some of the input energy is always lost or wasted as heat

the less energy that's wasted, the more efficient the device is

the efficiency of any device can be found using:

the efficiency can be written as a decimal (0.33) or a percentage (33%) by multiplying by 100

no device is 100% efficient and the wasted energy is usually spread out as heat (except heaters)

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ENERGY can be TRANSFERRED usefully from one form to another, STORED or DISSIPATED - but it can never be CREATED or DESTROYED

conservation of energy principle

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electrical energy - whenever a current flows

light energy - from the sun, light bulbs etc.

sound energy - from loudspeakers or anything noisy

kinetic energy - anything that's moving has it

nuclear energy - released from nuclear reactions

thermal/heat energy - flows from hot objects to cooler ones

gravitational potential energy - in stretched springs, elastic, rubber bands etc.

chemical energy - possessed by foods, fuels, batteries etc.

potential and chemical energy are forms of stored energy - it is waiting to be turned into another form

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Specific Heat Capacity

specific heat capacity is a measure of how much energy different materials can store

the specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C

you can work out the specific heat capacity of a substance using this formula:

E = m x c x Ø

E is energy transferred (J) m is mass (kg) c is specific heat capacity Ø is temperature change (°c)

water has a specific heat capacity of 4200 J/kg °c

materials used in heaters have high specific heat capacities so they can store large amounts of heat energy

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U-Values

a u-value is a measure of heat loss in a building element

the higher the u-value, the faster heat transfers through the material

the better the insulator, the lower the u-value

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Energy Efficiency in the Home

lots of heat energy can escape from a badly insulated home

there are many things you can do to a building to reduce this heat loss

the most effective methods of insulation are ones which give the homeowner the biggest annual saving

cavity wall insulation is foam squirted into the gap between bricks and this reduces convection and radiation across the gap

loft insulation is a thick layer of fibreglass wool laid out across the whole loft floor and this reduces conduction and radiation into the roof space from the ceiling

draught proofing is strips of foam and plastic around doors and windows to stop draughts of cold air - reducing heat loss due to convection

hot water tank jacket reduces conduction and radiation

thick curtains are big bits of cloth over windows to reduce heat loss by conduction and radiation