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P1 Physics Revision

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Grace Donnelly

on 18 October 2012

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Transcript of P1 Physics Revision

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli Revison P1 Physics Energy transfer by heating. Using Energy. Generating Electricity. Musical sounds. Waves. Electromagnetic Waves. Radiation Conduction Infrared: Surfaces: Solids: Gases: Liquids: Every object emits infrared radiation .The hotter the object is the more infrared radiation it emits. Radio waves microwaves infrared radition visible light ultra violet rays and x-rays are all parts of the electromagnetic spectrum. Light shiney surfaces emits less radiation than a dark matt surface. Shiny surfaces absorb less and reflects more radiation than a matt surface. Light shiny surfaces absorb less radiation than dark matt surfaces as well as reflecting more radiation than dark matt surfaces. States of matter Has no flow a fixed shape and volume. Much higher density than a gas. A liquid becomes a solid by soildifying or freezing. A solid turns into a gas by sublimation. Particles are in contact with each other but move randomly. Has an higher density than gas and a fied volume. Can be changed into a solid by freezing or solidifying. Can be changed into a gas by vaporizing or boiling. Doesn't have a fied shape flows and the volume can be changed. The particles are usually far apart and move quickly and randomly. Has a low density compared to solids and liquids. Turns into a liquid and a solid by condensation. Conduction is when the end of a material is heated the particles at the end gain kinetic energy and vibrate more.This energy is passed through the particles and the energy gets transferred through the material. Conduction happens mainly in solids. Most liquids and all gases are weak conducters. Metals conduct better than non-metals. Cooper is a better conductor than steel. Wood conducts better than glass. Evaporation and condensation Convction Energy transfer by design Evaporation is when a liquid turns into a gas. Condensation is when a gas turns into a liquid. Convection occurs in fluids (liquids and gases). Evaporation: Condensation: When a fluid is heated it expands and becomes less dense and rises.The warm fluid is replaced by a cooler denser fluid. This results in a convention current that transfers energy in the fluid. Convection currents are responsible for onshore and offshore breezes. The rate of evaporation is increased by :
-increasing the surface area of the liquid
-increasing the temperature of the liquid
-creating a draught of air across the liquids surface. The rate of condensation is increased by:
-increasing the surface area
-reducing the surface temperature. The greater the temperature difference between an object and its surroundings the greater the rate at which energy is transferred The materials, the objects shape and the surface area depends on the rate the energy is transferred. Specific Heat Capacity. Heating and insulating buildings. When we heat a substance the transfer energy will increase its temperature. The specific heat capacity of a substance is the amount of energy used to raise the temperature of 1 kilogram of the substance by 1 degree Celsius. You can reduce the energy at home by loft insulation, cavity wall insulation, aluminum foil, double glazed windows and solar panels. By using U-values we can compare different insulating materials.This is the energy per second that passes through one square meter of material when the temperature difference across it is 1oC. Forms of Energy. Magnetic, kinetic, heat,light,sound,nuclear and electric are all forms of energy. Gravitational potential,elastic potential and chemical are energy forms that can be stored. Energy can be transferred from one form to another. Light Energy:
Chemical energy in battery- electrical energy- light energy + energy heat surroundings. Conservation of energy. It is not possible to create or destroy energy it is only possible to transfer one energy form to an other or from one place to the other. Eamples of this are:
When an object falls gravitational potential energy is transferred to kinetic energy.
Stretching an elastic band transfers chemical energy to elastic potential energy. The total amount of energy is always the same this the conservation of energy and it applies to all energy transfers. Useful energy. A machine is something that transfers energy from place to an other or from one place to an other. The energy we get out of a machine consists of useful energy which is transferred to the place we want and in the form we want it and wasted energy which is not usefully transferred. Useful energy and wasted energy transfer to the surroundings and warm them up.Energy is wasted because the friction between the moving parts of the machine this energy warms the machine and its surroundings.Sometimes friction may be useful like in the brakes of a car,because some of it the kinetic energy is transferred to energy that heats the brakes. Energy
and efficiency. Energy is measured in joules (J) for all forms of energy. The energy is often called input energy.
Input energy (energy supplied)=useful energy transferred +energy wasted. The less energy wasted by an machine the more efficient it is.
Efficiency =useful energy transferred by the appliance
_________________________________(100%)
total energy supplied to the appliance. No machine can be more than 100% efficient because we can never get more energy from a machine than we put into it. The energy transfer through an appliance can be represented with a Sankey diagram. Electrical Energy. Electrical appliances. Electrical appliances are very useful they transfer electrical energy into any form of energy we need at the flick of a switch. They also waste energy to:
-Lamps waste heat energy.
-Electric miers waste sound energy.
-Speakers waste heat energy.
-Televisions waste heat energy. Common electrical appliances include:
-Lamps to produce light.
-Electric miers to produce kinetic energy.
-Speakers to produce sound energy,
-Televisions to produce light and sound energy. Lots of electrical appliances transfer by heating this may be a useful transfer like in kettles but energy is often wasted.Appliances should be designed to waste as little energy as possible. Electrical power. Body The power of an appliance is the rate at which it transfers energy.The unit of power is the watt (W). An appliance with a power of 1 watt transfers 1 joule of electrical energy to other forms pf energy every second.A watt is often too small a unit to be useful so power may be given in kilowatts (kW) 1 kilowatt=1000watts. Power is given by the equation:
P
-
t
p is the power in W
E is the energy in J
t is the time taken in seconds for the energy to be transferred. Power is the energy per second transferred or supplied so we can write the efficiency equation in terms of power
efficiency =useful power out
------------(100%)
total power in . Using Electrical energy. Companies charge customers for the amount of electrical energy used because of the large numbers involved the joule is not a suitable amount.The amount of energy measured is in kilowatt-hour (KWH). This equation is used to work out the energy in (KWH) transferred by a mains appliance in a certain time. Equation: E=pxt
E=the energy transferred in KWH
P=the power transferred in kW
T=the time taken (hours) of energy to transfer. Cost Effectiveness Matters. To compare the cost effectiveness od difference appliances we must consider a number of different costs.
These may include :
-The cost of buying the appliance.
-The cost of installing the appliances.
-The running costs.
-The maintenance cost.
-The enviromental costs.
-The interest charged on a loan to buy the appliance. Fuel for Electricity. In most power stations water is heated to produce steam.The steam drives the turbine which is coupled to an electrical generator that produces electricity.The energy can come from a burning fossil fuel like coal,oil or gas.Fossil fuels are obtained from ,long dead biological material.In some gas fired power stations hot gassess may drive the turbine directly .Gas fired turbines may be switched on quickly. Energy from wind and water. Wind:
-Wind and water can drive a turbine directly.
-In a wind turbine the wind passing pushes the blades to drive the geneerator at the top of the narrow tower. Hydroelectric Power:
-At a hydroelectric power station the water is collected in a reservoir.The water is allowed to flow downhill and turn the turbines and the bottom of the hill. Power from the Sun and Earth. Solar energy from the sun travels through space to the Earth as electromagnetic radiation. Geothermal energy is produced inside the Earth by radioactive processes and this heats the surrounding rock.In volcanic or other suitable areas very deep holes are drilled and cold water is pumped down to the hot rocks.There it is heated and comes back to the surface as steam.The steam is used to drive turbines that turn generators producing electricity. A solar cell can transfer this energy into electrical energy.Each cell only produces a small amount of electricity so they are useful to power small devices. A solar power tower uses thousands of mirrors to reflect sunlight onto a water tank to heat the water and produce steam. Energy and the Environment. Coal,oil,gas and uranium are non-renewable energy sources.They are being used up much faster than there being produced. Renewable energy resources will not run out they are produced as fast as they are used.Scientists are trying to find ways to reduce the environment impact of using fossil fuels. There are advantages and disadvantages to using each type of energy resources. National Grid. In Britain electricity is distributed through the national grid this is a network of pylons and cables that connect to buildings.Power stations in Britain can be switched in or out of the grid according to demand. The national grids voltage is 132000V or more power stations produce electricity at 25000V. In power stations electricity is generated at a certain voltage the voltage is increased by step-up-transformers before the electricity is transmitted across the national grid this makes the system more efficient. Its dangerous to supply electricity consumers at high voltages so local substations use step-down-transformers to reduce the voltage to 230V for uses at home. Big energy issues. A constant amount of electricity is provided by nuclear coal-fired and oil-fired power stations this is a base load demand. Demand is met using gas-fired power stations pumped-storage schemes and renewable energy sources.When demand is low energy is stored by pumping water to reservoirs. Different types of power stations different start-up times gas-fired power stations have the shortest start-up times nd nuclear power stations have the longest. We use waves to transfer energy and information the direction of travel of the wave is the direction in which the wave transfers energy.There are two types of waves a transverse wave and a oscillation (vibration) of the particles is perpendicular at its roght angles to the direction in which the wave travels.For a longitudinal wave the oscillation of the particles is parallel to the direction of the travel of the wave .A longitudinal wave is made up of compression and rarefactions. The nature of waves. Measuring waves. The amplitude of a wave is the height of the wave crest or the depth of he wave trough from the position at rest.The wavelength of a wave is the distance from one crest to the net crest.The frequency of a wave is the number of a wave is the number of wave crests passing a point in one second.The unit is measured in hertz (Hz) this is equivalent to seconds. The speed of a wave is given by the equation : v=f wavelength in meters. V is the wave speed in meters per seconds m/s.F= the frequency in hertz. Reflection. The image seen in a mirror is due to reflection of light.We draw a line called the normal perpendicular to the mirror at the point where the incident ray hits the mirror.The normal line is perpendicular to the mirror where the incident ray hits the mirror.The angle of incidence is the angle between the incident ray and the normal.The angle of reflection is the angle between the reflected ray and the normal. Refraction. Waves change speed when they cross a boundary between different substances.Refraction is a property of alll waves including light and sound.The change in speed of waves causes a change in direction.When light enters a more dense substance it slows down nd the ray changes direction towards the normal.When it enters a less dense substance it speeds up and the ray changes direction away from the normal. Diffraction. Diffraction is a property of all waves including light and sound.It is spreading of waves when they pass through a gap or round an obstacle.The effect is noticeable if the wavelength of the wave is about the same sie as the gap or obstacle. Sound. Sound is caused by mechanical vibrations in a substance and travles as a wave that can travel through liquids solids and gases but cant travel through a vacuum.Sound waves are longitudinal waves.The range if frequencies that humans can hear is from 20to20000Hz.Sound waves can be reflected to produceechoes only hard flat surfaces can refract it soft things will only absorb it. The pitch of a note depends on the frequency of the sound waves the higher the frquency the higher the sound.The loudness depends on the amplitude of the waves the greater the amplitude the louder the sound.Differences in waveform can be shown on an oscilloscope. The electromagnetic spectrum. Electromagnetic radiations are electric and magnetic disturbances which travel as waves and move energy from place to place.All electromagnetic waves travel through space at the same speed but differ in wavelengths and frequencies.
All electromagnetic waves travel through space at a wave speed of 300 million m/s we link the speed of the waves to their wavelength and freqyency by using:
v=f wavelength in meters.
v=the wave sped
f=frequency in hertz. Light,infrared,microwaves and radio waves. Visable light is the part of the electromagnetic spctrum detected by our eyes we see the different wavelengths as colours.The wavelength increases across the spectrum from violet to red we see s mixture of colours as white light.Microwaves are used in communications.Microwaves transmitters produce wavelengths that are able to pass through the atmosphere.Radiowaves transmit radio and TV programs and carry mobile phone signals. Communications. Radio and the microwave spectrum is divided into different bands and are used for different purposes.The shorter the wavelength of the waves the more information they carry the shorter their range the less they spread out.
Optical fibres are used to transmit signals carried by visible light or infrared radiation they are useful because they y more information and are secure. The expanding universe. The doppier effect is when a wave source is moving to an observer and the frquency of the observer changes from the original produced by the source. When the source moves away from the observer the observed wavelength decreases and the frequency increases the opposite happens when the source moves towards the observer.The further away the galay the bigger the red shift. The Big Bang. Red-shift tells us that the universe is epanding outwards in all directions.This suggests that it started with a big eplosion at a very initial point.If the universe began with a big bang then high energy gamma radiation would have been produced.As it epanded this would have become lower energy radiation.Scientists discovered microwaves coming from every direction in space this is cosmic microwave background radiation this was produced by the big bang.
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