November – December 2011 PHYSICS 1 Revision

Introduction Past Paper pack Mark schemes Revision Guides Moodle Kerboodle Revision time in lessons (not updated)

Why do I need to revise? Practice exam questions Learn content for exam Identify weaknesses – through your own analysis Identify weaknesses – through teacher feedback Exam technique Timing

Overview of PH1 1.1 Transfer of Energy by Heating processes 1.2 Energy and Efficiency 1.3 The Usefulness of Electrical Appliances 1.4 Methods we use to Generate Electricity 1.5 Waves Infra Red Kinetic Theory Heating and Insulating Buildings Conduction, Convection, Evaporation Energy transfers and Efficiency Transferring Electrical Energy Generating Electricity The National Grid General Properties of Waves ReflectionSoundRedshift

Infra Red Type of heat transfer – “radiation” The hotter an object is, the more infra red radiation is emitted Dark, matt surfaces – good emitters and good absorbers of IR radiation Light, shiny surfaces – poor emitters and poor absorbers of IR radiation Light, shiny surfaces – good reflectors of IR radiation Travels through space (e.g. from the Sun)  IR waves are part of the EM spectrumEM spectrum Also see CMBR (evidence of Big Bang) CMBR Lots of applications – see exam Qs

Kinetic Theory Particles of solids, liquids and gases: Have different arrangements Have different amounts of energy Solids: Regular, ordered, rows, close to neighbours Vibrations only Liquids: More random, jumbled, close to neighbours Vibrations, some swapping Gases: Move very quickly in straight lines until they collide No order, lots of space between neighbours Occupy all of container  Needed to explain conduction, convection, evaporation conduction, convection, evaporation

Conduction, Convection, Evaporation, Condensation (1) Solids are better conductors than liquids Gases are insulators Conduction works in solids by vibrations being passed on Metals conduct best because they also use free electrons to carry the thermal energy Convection only works in liquids and gases: When heated, particles move faster and move apart more making the fluid less dense Less dense fluids rise, carrying the thermal energy upwards Cold fluid is pushed down by rising hot fluid Use Kinetic Theory to explain why in terms of arrangement & movement of particlesKinetic Theory DO NOT say particles expand!

Conduction, Convection, Evaporation, Condensation (2) When the fastest particles break free of a liquid this is evaporation The liquid is cooler as a result Evaporation can be increased by: Blowing across the liquid surface Warming up the liquid Increasing the surface area Condensation is the opposite of evaporation The fast moving particles turn back to liquid giving their energy to the surface (warming it up) Graph of particle speeds to shows fastest ones escape

Conduction, Convection, Evaporation, Condensation (3) Heat transfer can be increased by: Increasing surface area Using a conducting material Dark matt surface Bigger temperature difference  Elephants ears help radiate heat – large surface area and dark Polar bears have white, thick fur and small surface area for their volume

Heating and Insulating Buildings The lower a U value a material has, the better the insulator The best insulators often have trapped pockets of air Payback time is the number of years it takes for the cost to equal the savings Solar panels contain water which is heated by the Sun for domestic heating and hot water The Specific Heat Capacity of a material is the amount of energy needed to raise the temperature of 1kg by 1  C E = m  c    Be ready to compare different ways of reducing heat losses m = mass (kg) c = SHC (J/kg/  C)  = temp. change (  C) Water has high SHC – great for carrying heat energy in central heating

Energy Transfer and Efficiency Energy can be transferred usefully, stored or wasted, but cannot be created or destroyed Wasted energy spreads out (“dissipates”) into the surroundings, which become warmer Only part of the energy transferred by a device can be used usefully, the rest is wasted Efficiency =  Practice using Sankey Diagrams Efficiency can be stated as a percentage or as a decimal

Transferring Electrical Energy Be able to describe energy transfers by everyday electrical appliances Energy used = Power  Time Energy used by mains electricity is measured in kilowatt-hours (kWh) 1 kilowatt-hour is the amount of energy used by a 1kW appliance in 1 hour 1kWh = 1kW  1hour Cost = cost per kWh  number of kWh  Block diagrams or Sankey Diagrams Don’t forgot to use kilowatts and hours!

Generating Energy (1) Be able to evaluate different methods of generating electricity in terms of: Start-up time (Hydroelectric and gas quick, coal and nuclear very slow) Cost of producing electricity Total cost including building and decommissioning (dismantling) Reliability Other advantages and disadvantages, including environmental Matching supply with demand: Ways of increasing supply, or Ways of decreasing demand NEVER use phrases such as “Eco- friendly” or “Green”

Generating Energy (2) Thermal Power Stations use an energy source to heat water into steam. A turbine then drives a generator Fossil fuels (coal, oil, gas) Uranium and plutonium (using nuclear fission) Biofuels (such as chicken droppings or crops grown especially). Biofuels are renewable Nuclear fission is not the same as nuclear fusion

Generating Energy (3) Renewable energy sources will not run out Wind, hydroelectric, tidal and wave turn turbines directly Wind can be unreliable Solar power (Solar cells, aka Solar PV) turn light energy directly into electrical energy Solar only works in day time and is dependent on cloud cover Geothermal uses hot rocks under the Earth’s surface (usually in volcanic regions) to create steam to drive turbines Rocks are hot due to radioactive decay DO NOT say “can be recycled” Some people consider wind turbines are an eyesore and noisy Solar power, wind and small-scale hydroelectric can be used in remote areas

Generating Energy (4) Environmental problems such be described specifically as follows: Release of harmful substances into the atmosphere (e.g. fossil fuels) Production of waste materials (e.g. nuclear waste) Noise and visual pollution Destruction of wildlife habitats (e.g. tidal and hydroelectric) Biofuels are considered carbon-neutral as they take out CO 2 from the atmosphere as they grow Carbon Capture and Storage is a growing technology, (e.g. storage of CO 2 in disused North Sea Oil and Gas fields)  CO 2 causes global warming Sulphur dioxide released by burning coal causes acid rain NEVER use phrases such as “Eco- friendly” or “Green” Flooding can destroy feeding habitats

The National Grid Consumers receive electricity via the National Grid For a given power, higher voltage reduces the current required and the energy losses At the power station end, a step up transformer increases the voltage At the consumer end a step down transformer reduced the voltage  Be able to label a National Grid diagram

General Properties of Waves (1) Waves carry energy Know the terms wavelength, frequency and amplitude Wave equation (all waves obey this): Speed = frequency  wavelength Waves can be transverse or longitudinal Sound waves are longitudinal Longitudinal waves show areas of compression and rarefaction Mechanical waves can be either transverse (water waves) or longitudinal (some earthquake waves) All waves can be reflected, refracted and diffracted Waves bend towards the normal when entering a slower medium Waves bend away from the normal when entering a faster medium In symbols: v = f  Frequency is measured in Hertz Diffraction is when waves spread out after travelling through a gap Diffraction is more pronounced when the gap size is close to the wavelength

General Properties of Waves (2) Electromagnetic waves are transverse em waves form a continuous spectrum (of which visible is only a tiny part) Learn the order of em spectrum: increasing frequency, increasing energy and decreasing wavelength: Radio, Microwave, IR, Visible, UV, X ray, Gamma Radio, Microwave, IR and Light are used for communications: Radio waves are used for TV and radio communication and can diffract around hills and buildings Microwaves are used for satellite TV and mobile phones Infra red are used in remote controls Visible is used in photography  All types of em wave travel at 300,000,000m/s in space (vacuum) Radio waves can have wavelength of 10 4 m, gamma rays can be m Be able to evaluate possible risks of using mobile phones

Reflection The normal is a construction line perpendicular to the surface at the point of incidence Law of Reflection: Angle of incidence = Angle of reflection The image produced in a plane mirror is upright, virtual and laterally inverted  You need to be able to draw a ray diagram for this

Sound Sound waves are longitudinal They cause vibrations in a medium, which are detected as sound Human hearing ranges from 20Hertz to 20kHz Pitch is determined by frequency Loudness is determined by amplitude Echoes are reflected sound Sound travels at about 340m/s in air  Sound waves travel faster in solids and liquids

Redshift (1) The Doppler Effect occurs when a wave source moves towards or away from the observer When moving away from the observer, the observed frequency decreases (or the wavelength increases) When moving towards the observer, the frequency increases (or the wavelength decreases) The Doppler effect occurs with any type of wave, but the speed of an electromagnetic wave source needs to be high for the Doppler effect to be noticed (we only notice Doppler shifted sound) Examples are ambulance sirens, galaxies

Redshift (2) Light from most galaxies is observed to have a longer wavelength than expected This is called Red Shift because the visible light shifts towards the red end of the spectrum This suggests most galaxies are moving away from us More distant galaxies are found to have a larger red shift and are therefore moving faster Red shift provides evidence for the Big Bang Theory, where the Universe is thought to have expanded from a single point Cosmic Microwave Background Radiation (CMBR) is evidence which also supports the Big Bang Theory CBMR comes from radiation present shortly after the beginning of the Universe  The Universe is thought to have begun more than 14 billion years ago