Physics Aqa P1A

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P1a

1.1 Thermal Radiation

* Thermal or heat radiation is the transfer of energy by infra-red waves. * Thermal radiation is energy transfer by electromagnetic waves. * All objects emit thermal radiation.
* The hotter an object, the more thermal radiation it emits. * Heat radiation can travel through a vacuum.

1.2 Surfaces and Radiation

* Dark, matt surfaces are better emitters of thermal radiation than light, shiny surfaces. * Dark, matt surfaces are better absorbers of thermal radiation than light, shiny surfaces.

1.3 Conduction

* Conduction mainly occurs in solids. Most liquids and gases are poor conductors. * Conduction in a metal is due mainly to free electrons transferring energy inside the metal. * The particles gain kinetic energy and vibrate more; this is then passed onto neighbouring particles etc. * When metals are heated free electrons gain kinetic energy and move through the metal and transfer energy by colliding with other particles. * Non-metals are poor conductors because they do not have free electrons. * Fibreglass is a good insulator because they contain pockets of trapped air.

1.4 Convection

* Polymers can be designed with specific properties by choosing different monomers and by changing the conditions used to make them

1.5 Heat Transfer by Design

* A radiator has a large surface area so heat can be lost easily. * Small objects lose heat more easily than large objects. * Heat loss from a building can be reduced by using:
* Aluminium foil behind radiators.
* Cavity wall insulation.
* Double glazing.
* Loft insulation.
* Using shiny, light surfaces which are poor emitters of heat. * Trapping air in small pockets.
* To maximise heat loss to keep things cool we can use:
* Good conductors.
* Paint objects dull black.
* Have air flow around them maximised.

TEST
1) Name 3 types of heat transfer.
2) Which type of heat transfer occurs mainly in solids?
3) How are convection currents set up in fluids?
4) Describe the process of heat transfer through a metal. 5) What factors affect the amount of heat radiated by a body? 6) Why are gases poor conductors?
7) How does surface colour affect the rate of conduction? 8) Why do central heating radiators have large surface areas? 9) Why does a concrete floor feel colder to your feet than a carpeted floor at the same temperature? 10) Why are hot water tanks often wrapped in glass fibre jackets?

2.1 Forms of Energy

* Energy can transform from one form to another.
*
Light| From the Sun or a lamp.|
Thermal| Flows from a hot object to a cold object.|
Sound| From a loudspeaker or a voice.|
Kinetic| Anything moving.|
Nuclear| From nuclear reactions.|
Electrical| Whenever an electric current flows.|
Gravitational Potential| Stored in any object that can fall.| Chemical| Stored in fuels, food and batteries released when chemical reactions have taken place.|

2.2 Conservation of Energy

* Energy can be transferred from one place to another.
* The total amount of energy is always the same (this is the conservation of energy). * E.G. when an object falls, GP (gravitational potential energy) is transformed into kinetic energy.

2.3 Useful Energy

* 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.
Input Energy = Useful Energy + Wasted Energy
Input Energy = Useful Energy + Wasted Energy

* As energy spreads out, it gets more and more difficult to use for further energy transfers. 2.4 Energy and Efficiency

* Energy is measure in joules (J)
* The less energy waster by a device the more efficient the device is. * Wasted energy causes inefficiency.
* No device can be 100% efficient except an electric heater, which...
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