Physics P1a revision - all topics

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  • Created by: MPR
  • Created on: 20-10-10 19:44

radiation, conduction, convection

Thermal Radiation:
-transfer of heat energey by infra red waves -no particles are involved, works in a vacuum
-Dark, matt=good absorbers and emiters
-Light, shiny= poor absorbers and emits
-Larger surface area (thin, flat) radiates more heat energy
-the hotter an object, the more heat it emits
-An object that is warmer than surroundings, loses heat energy and cools down.
-An object that is cooler than surroundings, gains heat energy and warms up.

Conduction: (solids only)
-if one end of a solid is heated the partiles gain kinetic energy, vibrate more. The energy is passed on to neighbouring particles.
-METALS: coduction occurs faster bc metals have free electrons. These gain kinetic energy and can freely move, as well as having vibrating particles.

Fluids (does not work in any solids bc particles are not free to move)
-Fluid is heated, partiles move away from each other, becomes less dense and rises. Cool -liquid: particles move close together, becomes dense, sinks.

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max/min heat loss & vacuum flask

  • Maximising heat loss:
    good conductors
    painted dull black
    maximised air flow
    Reducing heat loss In a House:
  • BY CONDUCTION: using insulators eg trapping a layer of air - double glazing/cavity wall insulation
  • BY CONVECTION: preventing convection currents e.g trapping air in small pockets- fibre glass
  • BY RADIATION: using poor emitters e.g. light, shiny surfaces - aluminium foil behind radiators

The vacuum flask:

  • there is vacuum between two wall of the container- stops conduction&convection
  • Liquid is in a glass container. Glass - insulator- stops conduction
  • Silverly glass surfaces - poor emitter-stops radiation from the outer wall
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Energy forms and efficiency of a device

-There are 9 forms of energy
-CONSERVATION OF ENERGY -Not possible to create or destory energy. It only transforms/transfers

A device transfers energy from one place to another/transfers energy.
-Input energy= useful + wasted energy
-Both useful and wasted energy is transformed to the surroundings, making them warm up
-As the energy spreads out, it becomes more diffucult to use it.
-Wasted energy is ofetn heat if it has moving parts (due to friction). Sound is also ofted wasted energy
-Devices have vents so that the wasted (heat) enery will warm surroundings/not overheat it.

Efficieny - useful energy transformed (J)  / total input energy (J)

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mains: power, energy transferred, cost of energy,

Electrical devices -transform electric energy to whatever form
-POWER - rate at which a device transforms energy. the faster the rate, the more powerful the device
-power (W) = energy transferred (J) / time (s)
-one watt= one joule per second 
-one kW=1000 W

Think mains electricity -
-energy transferred (kWh) = power (kW) x time (h)
-total cost= energy transferred (kWh) x cost per kWh
-electicity meter- records no of kWh used.
Current reading - previous reading = energy used between readings

National Grid:
step up transformer- increase voltage, decrease current =reduce energy loss,more efficient
step down- decrease voltage, increase current = safer for consumers

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Generating electricity

-power stations: burning fuel/heats water to produce steam, steam drives turbines, drives generators, produce electricity.
(coal- co2&so2)(oil-co2&so2)(gas -co2, starts up quickly)
-nuclear power stations- uranium/plutonium used. The nucleus undergoes nuclear fission which releases heat energy. This energy turns water into steam etc.
-more energy from each kg of nuclear fission than fossil fules
-no polluting gases but nuclear waste, risk of big accidents
-Wind and water- drive turbine directly
(turbine- dilute, sound/visual pollution) (hydroelectric- pumped storage system, starts up quickly, must be wet and hilly, flooding) (waves- hazardous to boats) (tides -reliable, affects ecology)
-Earth and Sun- (solar- coverts electromagentic radiation into electrical energy/ heats water flowing through/ light to electric, dilute)
(geothermal- radioactive processes heat rocks. hot water comes to the surface-heats buildings). (naturally in some places or deep holes are drilled, cold water is pumped down. steam comes up) Steam drives turbines etc, only in few places,

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Sabah Ijaz

omggggggggggggggggg, amazing :)

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