Physics
- Created by: GeorgiaThorne
- Created on: 21-04-14 11:08
Conduction & Convection
Condution
The atoms/particles vibrate more in high temperature than low temperature. They hit each other sending energy. Because the electrons are free to move they can pass energy much faster
Convection
Convection currents happen in liquids, because the particles move faster. This enables the particles to move away from each other and causes the liquid or gas to expand becoming less dense. Less dense liquids rise up
Kinetic theory of matter
SolidLiquidGas Arrangement of particles
close together
regular pattern
close together random
far apart
random
movement of particles vibrate about a fixed position move around each other move quickly in any direction diagram
Evaporation and condensation
Evaporation
The particles in a liquid have different energies. Some will have enough energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens. This is why sweating cools you down. The sweat absorbs energy from your skin so that it can continue to evaporate
Condensation
The particles in a gas have different energies. Some may not have enough energy to remain as separate particles, particularly if the gas is cooled down. They come close together and bonds form between them. Energy is released when this happens. This is why steam touching your skin can cause scalds: not only is the steam hot, but energy is released into your skin as the steam condenses
Infrared radiation
Radiate - to spread out from a source
Radiation - the energy that spreads out
Absorbs best Dull black Emits best
Shiny black
White
Absorbs worst Silver Emits worst
Specific heat capacity
Specific heat capacity - amount of energy it takes to heat something up
Specific heat capacity = energy input
mass = temperature x rise
Energy transfer & efficiency
Kinetic
Graviational potential
Elastic strain
Heat
Light
Sound
Electrical
Chemical
Nuclear
Sources of energy
Solar
Tidal
Waves
Hydroelectric
Wind
Fossil fuels -
Coal
Oil
Geothermal
Biomass (food)
Notes on unit 1.1 & 1.2
Diffusion - When smell spreads out across a room
Thermal radiation - The transfer of energy by electromagnetic waves
U-values - Measure how effective a material is as an insulator. The lower the u-value the better the material is at insulating
Energy cannot be created or destroyed
Friction - Energy is often wasted as heat losses caused by the force of friction. Friction can be reduced by lubrication and streamlining
Changes of state
The vacuum flask
1. The stopper reduces energy transfer by convection, gases cannot rise or sink past the stopper 2. The vacuum reduces energy transfer by conduction and convection, there are no particles to transfer the energy 3. The silvery surfaces reduce energy transfer by radiation, reflecting back the energy
Power
Power = energy transferred
time taken
Generating electricity
A typical power station
Boiler -> Turbine -> Generator -> National grid
Boiler - An energy source is used to heat water - Chemical energy to heat energy
Turbine - The steam produced drives a turbine - Heat energy to kinetic energy
Generator - A tubine that is coupled to an electric generator - Kinetic energy to electrical energy
Alternative Energy
There are a number of alternative sources of energy...
Wind Tides Geothermal
Waves Sun Biomass
Hydroelecric dams
These sources are renewable
Wind and water can be used to drive turbines directly
Alternative Energy sources
Solar, wind, tidal, waves, hydroelectric, geothermal, biomass - water related
Convection current - Air is heated by the sun and rises off the equator. Cooler air moves in, moving air = wind
The National Grid
Power station -> Tranformer (step up) -> Transmission -> Transformer (step down) -> transmission -> transmission -> transformer (step down) -> transformer (step down) -> transformer (step down) -> Schools, homes, offices and shops
Step up voltage - reduces current
Less current - wires not so hot - less energy wasted
Step down voltage - safe to use
Waves
Waves transfer energy without any matter being transferred
Wavelength - the distance between a particular point on one wave and the same point on the next wave
Amplitude - the maximum disturbance caused by a wave
Frequency - the number of waves passing each second, measured in hertz, Hz
Wavespeed = frequency x wavelength
metre/second hertz metre
m/s hz m
Longitudinal waves
Example - sound waves travel through solids, liquids and gases as longitudinal waves
Transverse waves
Reflection
Light from the sun reflects off the tree and into our eyes
Types of relfection -
Normal reflection occurs at smooth surfaces like the water and produces an image
Diffuse reflection occurs at rough surfaces like the building and the light is scattered
Reflection (Part 2)
A flat mirror is called a plane mirror. We always measure angles from the normal
Notes
Angle of incidence - the angle between the incident ray and the normal
Angle of reflection - the angle between the reflected ray and the normal
Law of reflection - angle of incidence is equal to the angle of reflection
Real and virtual images - rays of light pass through a real image but only appear to come through a virtual image
Refraction
Rays of light change direction (are refracted) when they cross the boundary between one transparent medium and another, unless they meet the boundary at a right angle. Waves are not refracted if travelling along the normal
Diffraction
When a wave moves through a gap, or past an obstacle, it spreads out from the edges
Straight waves are called plane waves
If the gap is a similair size to the wavelength, the diffraction is more significant
Waves having a longer wavelength are more strongly diffracted
Sound
Sound doesn't travel through a vacuum
Sounds result when objects vibrate
Soundwaves are longitudinal waves and cause vibrations in a medium (material), a series of compressors and rarefactions
Humans can hear sounds in the range of 20Hz to 20000Hz
Infrasound - sound lower than humans can hear
Ultrasound - sound louder than humans can hear
Sound waves are shown on an oscrilloscope
The pitch of a sound is determined by it's frequency. The higher the number of vibrations the higher the pitch
The pitch of a sound is determined by it's loudness by it's amplitude. The greater the size of the vibrations, the louder the sound
Electromagnetic spectrum
Radiowaves
The shorter the wavelength - the more information they carry
the shorter their range in air - due to their increasing absorption in the air
The less spread out, the less diffraction
Radio wavelengths -
less than 1m - tv from terrestrial masts, the waves can carry more information
between 1m & 100m - local radio and emergency services
greater than 100m - national and international radio stations
Microwaves
Microwave radiation can pass through the earth's atmosphere to and from satellites. Microwave signals do not spread out or waken as much as radio signals
Mobile phone radiation
Mobile phone networks also send and receive information using microwaves. The mobile phone sends a signal to the mast which is then routed through the phone network to the receiving phone. The return is routed through the mast to the sending phone. The signals to and from the mast are carried by radio waves of different frequencies
Microwaves and Infra-red
Microwave waves are positive and negative which flips the water molecules and makes them hotter which cooks the food
All objects emit infrared radiation. The hotter the object, the more infrared radiation it emits. Infrared radiation is absorbed by the skin, heating it up. It can damage or kill skin cells
Fibre optic
The light is reflecting off the insides of the optical fibre which we call total internal relfection. By flashing the light off and on you can send messages/signals
Red shift & the Doppler effect
When an object moves away from an observer, its light is affected by the Doppler effect
The Doppler effect
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.
When a source moves towards an observer, the observed wavelength decreases and the frequency increases.
When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
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