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P1 Physics Revision
Transcript of P1 Physics Revision
In a liquid they move about at random but are in contact with each other.
In a gas they move about randomly and are much futher apart than particals in liquids of solids. Conduction,Convection and Radiation Metals are the best conductors of energy Materials such as wool and fibreglass are the best insulators of energy Conduction is mainly due to free electrons transferring energy inside a metal. Non-metals are poor conductors as they don'tcontain free electrons Convection is the circulation of a fluid (liquid or gas) caused by it being heated heating a liquid or gas makes it
less dense so it rises and causes
circulation After the fluid rises it is replaced by cooler, denser fluid. This is called a convection current. Dark, matt surfaces emit and absorb radiation more than light shiny surfaces. Light, shiny surfaces reflect more radiation than dark, matt surfaces. The rate of energy transfer to or from an object depends on: -the shape,size and type of
material of the object -the materials the object is
in contact with -the temperature difference between the object and its surroundings The greater the temperature difference, the greater the rate at which energy is transferred. Maximizing the rate of energy transfer keeps things cool. Minimizing the rate of energy
transfer keeps things warm. vacuum flask minimizes
the rate of energy transfer Specific heat capacity The greater the mass of an object, the more slowly its temperature increases when it is 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. Heating and insulating buildings The rate of energy transfer to or from our homes can be reduced through insulation, double glazing, drought excluders and several other ways. u-values tell us how much energy per second passes through materials. The lower the u-value the better Forms of energy Energy exists in different forms Energy can be transferred from one form into another. energy exists in : -light -sound -kinetic -nuclear -electrical -gravitational potential -elastic potential -chemical Conservation of energy Energy can't be created
or destroyed The total amount of energy in
something is always the same Useful energy useful energy is energy in the place we want it and the form we need it in wasted energy isn't useful Both types of energy end up being transferred to the surroundings, which become warmer as energy spreads out it gets more and more difficult to use for further energy transfers. example: for a music player the useful energy is sound and the wasted energy is heat coming off the object Energy and efficiency No machine can be
more than 100% efficient. measures to make machines more efficient include reducing: -friction -air resistance -electrical resistance -noise due to vibrations the less energy wasted by a machine, the more efficient it is Electrical appliances electrical appliances can transfer
electrical energy at the flick of a switch an electrical appliance is designed for a particular purpose so it should waste as little energy as possible Common electrical appliances include lamps, electric mixers, speakers and televisions Electrical power The power of an appliance is the rate at which it transfers energy. the units of power are watts and kilowatts Using electrical energy the kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour Cost effectiveness cost effectiveness means getting the best value for money to compare the cost effectiveness of different appliances, we need to take account of a number of different costs which include : cost of buying, cost of installing, running costs, maintenance costs and environmental costs. big energy issues Different
perspectives Fuel for electricity Coal, oil and natural gases are
burnt in fossil-fuel power stations electricity generators in power stations are driven by turbines. uranium or plutonium is used as a fuel in a nuclear power station but it isnt burnt; the energy comes from a process called NUCLEAR FISSION biofuels are renewable sources of energy which cane generate electricity boiler Energy from wind and water wind turbines are electricity
generators on top of tall towers waves generate electricity by turning a floating generator. hydroelectricity generators are turned by water running downhill a tidal power station traps each high tide and uses it to turn generators theses are all renewable sources, not fossil or nuclear fuels Power from the sun and earth solar cells transfer solar energy directly into electricity. Geothermal energy comes from inside the earth and is produced by radioactive processes that heat up the surrounding rocks In volcanic areas very deep holes are drilled and cold water is pumped down to the hot rocks. It is heated up and comes back to the surface as steam. solar heating panels use the sun's energy to heat water directly Energy and the environment burning fossil fuels produces greenhouse gases that cause global warming nuclear fuels produce radioactive waste using renewable energy resources can affect plants and animals renewable energy sources won't run out but non-renewable fossil fuels will eventually The national grid the national grid distributes electricity from power stations to our homes step-up and step-down transformers are used in the national grid a high grid voltage reduces energy wastage and makes the system more efficiect gas-fired power stations and pumped-storage power stations can meet variations in demand nuclear, coal and oil power stations can meet base-load demand. (cc) photo by theaucitron on Flickr The nature of waves transverse waves vibrate at right angles to the direction of energy transfer. All electromagnetic waves are transverse. longitudinal waves vibrate parallel to the direction of energy transfer. A sound wave is longitudinal. Mechanical waves can be either measuring waves the amplitude it the height of the wave crest or depth of the wave trough. the frequency is the number of wave crests passing a point in one second the wavelength is the distance from one wave crest to the next . this is the same as the distance from one wave trough to another. /crest wave reflection the law of reflection states that the angle of incidence is equal to the angle of reflection. a real image can be formed on a screen as the rays of light that produce the image actually pass through it. a virtual image can't be formed on a screen as the rays of light that produce the image only appear to pass through it. wave refraction refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances. refraction is a property of all waves, including light and sound if the speed is reduced, refraction is towards the normal is the speed is increased, refraction is away from the normal. wave diffraction diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle. the narrower the gap, the greater the diffraction if radio waves do not diffract enough when they go over hills, radio and TV reception will be poorer. diffraction is a property of all waves Sound waves the frequency range of a normal human ear is from 20Hz to about 20kHz sound can travel through solids, liquids and gases. The waves generally travel fastest in solids and slowest in gases sound can't travel
through a vacuum (space) only hard flat surfaces such as flat walls and floors reflect sound. soft things like carpets, curtains and furniture absorb sounds. Musical sounds the pitch of a note increases if the frequency of the sound wave increases. the loudness of a note depends on the amplitude of the sound waves. vibrations created in an instrument when it is played produce sound waves . <--low pitch <--high pitch the electromagnetic spectrum the electromagnetic spectrum includes: gamma ray, x-ray, ultraviolet, visible, infrared, microwaves, radio waves electromagnetic radiations are electric and magnetic disturbances all waves travel through space at the same speed but they have different wavelengths and frequencies the spectrum is continuous light, infrared, microwaves, and radio waves white light contains all the colours of the spectrum these waves are all used for communications visible light can be used for photography, also the wavelength increases across the spectrum from violet to red radio waves transmit radio and TV programs and carry mobile phone signals Communications optical fibres are very thin fibres that are used to transmit signals by light and infrared radiation the expanding universe light from different galaxies is RED-SHIFTED Red-shift provides evidence that the universe is expanding when a wave moves away from an observer, the wavelength increases and the frequency decreases when a wave moves towards an observer, the wavelength decreases and the frequency increases. the big bang the universe started with the big bang; a massive explosion from a very small initial point the universe has been expanding ever since cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the big bang