# Physics Unit 1

Energy transferred by heating

Using energy

Electrical energy

Generating electricity

Waves

Electromagnetic Waves

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• Created by: Amy
• Created on: 02-01-13 14:23

Infrared radiation is energy transfer by electromagnetic waves

The hotter an object, the more radiation it gives off

It can travel through a vacuum (this is how we get heat energy from the sun)

Doesn't involve particles

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Dark, matte surfaces emit and absorb radiation more quickly than light, shiny surfaces because they are absorbers. (I.e. black absorbs heat better than white and a black object would transfer energy and cool down more quickly.)

Light, shiny surfaces are good reflectors of infrared radiation

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## States of Matter

Flow, shape, volume and desnity are used to describe each state of matter

Solid - Particles are held next to each other, vibrating in their fixed positions

Liquid - Move at random and are in contact with each other

Gas - Move randomly and are far apart (less density)

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## Conduction

Occurs mainly in solids (most liquids and gases are poor conductors)

Metals are the best conductors

Wool and fibre-glass are the best insulators

If one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more, this energy is passed to neighbouring particles

When metals are heated their free electrons gain kinetic energy and move through the metal, transferring energy by colliding with other particles

Poor conductor = good insulator (no free electrons)

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## Convection

Occurs in fluids (liquids and gases)

When a fluid is heated, it expands, becomes less dense and rises. The warm fluid is replaced by cooler, denser fluid. The resulting convection current transfers energy throughout the fluid

Convection currents = Heating water in a beaker, heating the air above land and sea

Convection currents are responsible for onshore and offshore breezes

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## Evaporation and Condensation

Evaporation - when a liquid turns to gas because liquid molecles escape form the liquids surface and into the air. Therefore the kinetic energy of the remaining molecules is less so the temperature of the liquid decreases. Evaporation causes cooling.

Evaporation rates are increased by: Increasing surface area of liquid, increasing liquid temperature, draught of air across the liquids surface

Condensation - when a gas turns to liquid (on mirrors or windows e.g.)

Condensation rates are increased by: Increasing surface area and reducing surface temperature

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## Energy transfer by design

The greater the temperature difference between an object and its surroundings, the greater the energy transfer rate

The rate of energy transfer also depends on: The material the object is in contact with, the shape and surface area

To maximise the energy transfer to keep it cool you can use things which are: Good conductors, paited black, have the air flow around them maximised

To minimise the rates and keep things warm, use: Good insulators, white and shiny objects, prevent convection currents by trapping air in small pockets

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## Specific heat capacity

The greater the mass of an object, the more slowly its temperature increases when heated

The rate of temperature change in a substance when heated depends on the energy transferred to it, its mass and its specific heat capacity

The specific heat capacity is the amount of energy required to raise the temperature of 1 kg by 1 degree.

The greater the specific heat capacity, the more energy required for each degree temp. change

The equation for heat capacity =

Energy transferred (J) = Mass (Kg) X Heat capacity (J/Kg degreesC) X temp. change (degrees C)

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## Heating and insulating buildings

The rate of energy transfers to and from our homes can be reduced, which reduces fuel bills. This can be done by fitting: Fibreglass loft insulation to reduce energy transfer by conduction, cavity wall insulation that traps air in small pockets and reduces it through convection, double glazing reduces conduction, foil behind radiators reflects infrared radiation back into the home and draught excluders.

U-Values tell us how much energy per sec. passes through different materials. The lower the U-Value, the beter the insulator

Solar panels contain water that is heated by the sun and are expensive to buy and install and the water doesn't heat at night but cheap to run because they don't use fuel.

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