# Physics 1

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• Created by: a_nnmaria
• Created on: 08-05-16 16:07

## Moving and Storing Heat

Heat is a measure of energy (Joules)

Temperature is a measure of hotness (the greater the difference in temperature, the faster the rate of cooling will be.)

If there's a difference in temperature between two places, then energy will flow between them.

Specific heat capacity is the amount of energy neeeded to raise the temperature of 1kg of a substance by 1 degrees celsius.

Energy = mass x specific heat capacity x temperature change

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## Melting and Boiling

When a substance is melting or boiling, you're still putting in energy, but the energy's used for breaking intermolecular bonds rather than raising the temperature.

Specific Latent Heat of melting or boiling is the amount of energy needed to melt or boil 1Kg of material without changing its temperature.

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## Conduction and Convection in the Home

Conduction occurs mainly in solids.

Conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles.

Convection occurs in liquids and gases.

Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.

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Radiation is how we get heat from the sun.

All objects emit and absorb heat radiation.

Matt black surfaces are very good absorbers and emitters of radiation.

Light coloured, smooth and shiny objects are very poor absorbers and emitters of radiation.

Grills and toasters heat fiid by infrared radiation. The heat radiated by the grill is absorbed by the surface particles of the food, increasing their kinetic energy.

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## Saving Energy

Payback time is the money you've saved on energy bills will equal the intial cost.

Payback time = Intial cost/ annual saving

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## Waves

Waves have a amplitude, wavelength and frequency.

Amplitude is the displacement from the rest position to the crest.

Wavelength is the length of the full cycle of a wave

Frequency is the number of complete cycles or osciillations passing a certain point

Speed = frequency x wavelength

The law of reflection:

Angle of Incidence = Angle of Reflection

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## Diffraction and Refraction

Diffraction is waves spreading out.

The amount of diffraction depends on the size of the gap relative to the wavelength/ The narrower the gap, or longer the wavelength, the more wave spreads out.

Refraction is changing the speed of a wave can change its direction.

Waves travel at different speeds in substances which have different densities. So when a waves crosses a boundary between two substances it changes speed.

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## Communication

Communication can occur in many ways:

• Morse code
• Optical Fibres - they carry data over long distances as pulses of light or infrared radiation.

Multiplexing means lots of dfferent signals can be transmitted down a signal optical fibre at the same time.

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## Wireless Communication

Radio waves are good for transferring information over long distances.

Diffraction makes a difference to signal strength.  The amount of diffraction will depend on the wavelength of the wave.

Refraction can help radio waves travel further. Radio waves travel faster through ionised parts of the atmosphere than non-ionised parts. This is called refraction.

Microwaves are used for satellite communication.

Mobile phones use micrwaves and sometimes this can be harmful.

The absorption is harmful and the micrwaves are absorbed by water molecules in livin tissues, the cells could be killed.

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## Analogue and Digital Signals

Analogue signals vary but digital just on or off.

Analogue signals can take any value within a certain range. The amplitude and frequency of an analogue wave will vary continually.

Digital signal can only take two values. These values tend to be On/off.

• Digital and analogue signals weaken as they travel, so they might be amplified along their route.
• They can transmit several signals at the same time using one cable - multiplexing.

Interfernce is when two or more waves of a similar frequency meet, they can create one combined signal with a new amplitude.

This is called interference. You get it when two radio stations transmit on similar frequencies.

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## Humans and the environment

Ultraviolet radiation causes skin cancer.

Darker skin gives more protection against UV rays-it absorbs more UV radiation. This prevents some of the damaging radiation reaching the more vulnerable tssues deeper in the body.

Everyone should protect themselves from the sun, but if you're pale skinned, you need to take extra care and use sunscreen with high sun protection factor (SPF).

Ozone layer protects us from UV radiation.

The ozone layer absorbs some of the UV rays from the sun, so it reduces the amount of UV radiation reaching the earth's surface.

The depletion of the ozone layer allows more UV rays to reach us at the surface of the earth.

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## Seismic Waves

Seismic waves travel inside the earth and they produce types of shock waves.

P Waves

• Are longitudnal
• It can travel through solids and liquids
• They travel along the direction that a wave travels.

S Waves

• Are transverse
• It can travel only through solids
• They travel at right angles to direction the wave travels.

The wave curves with oncreasung depth. The wave chnage speed as the properties of the mantle and core change.

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