# Physics Unit 1

The amount of infrared radiation emitted or absorbed by an object depends on its temperature and its surface.

All objects EMIT and ABSORB infrared radiation. The hotter an object is, the more infrared radiation it gives out in a given period of time.

Dark, matt surfaces: Good emmiter , good absorber.

Light, shiny surfaces: Poor emmiter , poor absorber.

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## Kinetic theory:

The kinetic theory says that objects are made up of particles that are constantly moving.

The kinetic theory can be used to explain properties of solids, liquids and gases.

Solids: Particles can just vibrate in a fixed position. They have a fixed shape.

Liquids: Particles move around but stay close together, Liquids can flow.

Gases: Particles move fast and have lots of space between them. They fill to shapes and flow.

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## Changes of state:

When particles in a solid are given more energy, they can start to move around and become liquid.

When particles in a liquid are given more energy, they move apart and become a gas.

Particles in a gas have more energy than the same particles in a liquid, which in turn have more energy than the same particles in the solid.

The amount of energy in a particle relates to the temperature of the material.

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## Methods of transferring energy:

Energy is transferred from one place to another by CONDUCTION, CONVECTION and RADIATION and EVAPORATION and CONDENSATION.

Conduction: When particles in a solid are given more energy, they vibrate more. They colide with neighbouring particles, which causes these particles to vibrate more. In this way, energy spreads through the solid. In metals there are free electrons that help transfer the energy, making metals good conductors.

Convection: When particles in a liquid or gas are given more energy, they move faster and spread out. The density is lower so the hot material rises. It is replaced by cooler material so covenction currents occur.

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## Evaporation and condensation:

Evaporation: Causes cooling e.g. Nail varnish, sweating.

Energy is transferred in evaporation. Particles gain energy to change state, for                                example Liquid to gas.

Condensation: Causes heating e.g shower or bus windows.

Energy is transferred in condenation. Particles lose energy to change state. Water                         molecules in the air from breathing build up and as we breath hot air, it floats                                 around, hits the window then the cold air molecules cool down the hot air and it                             causes condensation.

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## Rate of energy transfer:

The bigger the temperature differnece between the object and the surroundings, the faster energy is transferred.

The rate at which energy is transferred to or from the object depends on:

• The material from which the object is made or the material it is packaged in. Insulators transfer heat more slowly.
• The surface area and volume of the object. Greater surface area means faster rate of energy transfer.
• The proporties of the surface of the object. Dull, dark surfaces emit or absorb radiation at a higher rate.

Evaporation takes place faster when the temperature is higher.

Polar bears keep warm with thick fur. The fur traps air so less energy is lost by convection. The fur is white so it radiates energy at a lower rate.

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## Keeping warm:

U-Values:

Energy is transferred through a material when the temperature on each side is different.

U-Values compare how much energy is transferred through materials in a given time.

The lower the U-Value the better the material as in insulator.

Metals have high U-Values. Wool and foam have low ones.

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## Specific heat capacity:

The SHC of a material is the amount of energy needed to raise the temperature of 1kg of the material by 1 degree.

E = m x c x 0 (Vita)

E= J

m= Kg

c= j/kg degree

Vita= Temperature change

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## Solar panels:

Solar pannels on roofs use the sun's energy to heat water. The hot water can be used for washingor to heat the house.

The pannels contain pipes.

Cold water enter the pipes and is heated up by the energy from the sun.

This energy passes from the heated water to cooler water in the tank over night.

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## Energy and efficiency:

Energy cannot be created or destroyed, but it can be stored or transferred in to useful forms.

Efficiency= Useful energy out / Total energy in

OR

Efficiency = Useful power out/ Total power in

Payback time = Cost of new appliance / Cost of energy saved each year

Payback time is the time taken for the cost of a more efficient appliance to be paid by reduced energy bills.

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## Electrical appliances:

The cost of using electrical appliances can be worked out if we know the amount of energy transferred in a given time.

Energy transferred in KWH - Power in Kilowatts x Time in hours

Energy transferrs:

Light bulbs: Electricity -> Light.

Kettles: Electricity -> Heat, Sound, Light.

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## Generating electricity:

Most of our electricity is generated using power stations that turn water into steam.

Power station fuels:

Energy sources for power stations include...

• Fossil fuels.
• Nucluear fission (Nucli releasing lots of energy).
• Bio fuels (Wood, straw, ethonol).

Supplies of some fossil fuels, will only last a few more deades.

Fossil fuels are NON-RENEWABLE.

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Wind turbines.

Hydroelectricty.

Tides.

Waves.

Geothermal.

Solar.

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## Environment and energy:

Coal mines, wind turbines ect: Visual pollution.

Burning fossil fuels: CO2 Pollution.

Habitats can be destroyed.

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## Distributing energy:

The National Grid:

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## Types of waves:

Transverse:   -> -> Direction of travel and energy transfer.

Longitudinal: -> -> Direction of travel and energy transfer. Compression and rarefraction. Air                                        particles more around to carry sound waves.

Mechanical: Must not move through solids, liquids or gases. They cannot travel through a vaccum.                     They may be transverse or longitudinal.

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## Electromagnetic waves:

Electromagnetic wavves are transverse waves that include light, radio and x-rays.

All of these waves travel at the same speed in a vaccum.

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## Hazards of electromagnetic waves:

Gamma and X rays cause cancer.

UV causes sunburn and skin cancer.

Visual can damage eyes.

Infrared can cause burning.

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## Communications:

Some electromagnetic waves are used in communication because the waves can carry information with the energy they transfer.

Microwave: Mobile phones and Satellite TV.

Infrared: Remote controls.

Visable: Photography.

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## Waves:

1- Reflection: When a wave bounces off the interface between two materials. The wave changes direction but does not cross the interface.

2- Refraction: Happens when a wave crosses an interface between two materials. The wave changes direction unless the rays hit the interface at right angles.

3- Diffraction: Happens when waves pass through a gap or over an object that is similar in size to the wavelength of the wave. The wave spreads out through the gap.

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## Sound waves:

Longitudinal that cause vibrations in materials.

They travel through medium material and can travel through any solid, liquids and gases.

The pitch of a sound is determined by its frequency.

A high pitched sound is a wave with a high frequency.

The loudness of a sound is related to the amplitude of the vibrations.

Echos:

Sound waves can be reflected off surfaces.

We hear the relections as echoes.

Echoes arrive after the main sound because the waves have travelled further.

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## Red shift:

The Doppler effect:

Used to measure the speed and direction of moving objects.

When a sound of a wave is moving, the waves infront of it get squashed.

Their frequency increases and wavelength decreases.

The waves become stretched and their frequency is lower and wavelength longer.

The faster the source moves, the bigger the change in frequency and wavelength.

If the source of a sound is moving towards us, we hear a higher pitched sound.

If the source is moving away, the sound is a lower pitch.

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## Red-Shift:

The radiation from stars in distant galaxy is at longer wavelemgths than the radiation from similar stars in our own galaxy... This is called red-shift.

Red-shift shows us that the galaxies are moving away from us.

The further the galaxies are from us the bigger the red-shift.

This means that the further away the stars are, the faster they are moving away from us.

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## The expanding universe:

Oberservations of red-shift provide evidence for theories about the universe.

Red-shift shows that the universe is expanding. The Big band theory suggests that he universe began from a tiny point and expanded to become what it is now.

The big bang theory predicts that the radiation released when the universe started to expand is still present.

As the universe expanded, the wavelength increased so that it is now microwaves.

This cosmic microwave background radiation (CMBR) has been observed and is evidence of the big bang theory.

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