P1 EXAM BRIEFING. Wednesday 23 rd May 2018, 1.30PM

Transcription

1 P1 EXAM BRIEFING Wednesday 23 rd May 2018, 1.30PM

2 ENERGY Topic 1

3 Energy Stores & Systems Energy is the property of matter and radiation which allows work to be carried out (such as making particles move). Energy can be transferred usefully, stored or dissipated (often called wasted), but cannot be created or destroyed. Energy before = energy after. Efficiency 100% Energy store Kinetic Thermal Chemical Gravitational Potential Elastic Potential Electrostatic Magnetic Nuclear Energy transfer Mechanically Electrically By heating By radiation Improve efficiency through lubrication & thermal insulation

4 Changes in Energy Work done (J) is the same as energy transferred

5 Energy Changes in Systems Higher thermal conductivity of material = higher rate of energy transfer by conduction across material. Describe how the walls of a building affect its rate of cooling and explain ways to reduce the energy transfer. [6 marks] A thicker wall will mean the building will cool more slowly [1]. A lower thermal conductivity of the material the wall is built from will mean the building will cool more slowly [1] - for example brick has a lower thermal conductivity than metal, so it is better to build walls out of brick [1]. Energy transfer can also be reduced by using thermal insulation - a material with low thermal conductivity [1]. Cavity walls (two walls with a gap between them) will reduce heat transfer [1] as the cavity contains an insulator (air or another suitable insulator) [1].

6 Required Practical Insulation IV: type of material DV: temperature decrease ( C) CVs: volume of water (cm 3 ), temperature of surroundings ( C) 1. Wrap the first insulating material (thick foam) around and below a 100ml beaker. Place this inside a 250ml beaker for support. 2. Make a cardboard lid for the small beaker. Ensure it has a hole for the thermometer and that the thermometer will reach into the water. 3. Put 50ml of 80 C water in to the beaker using a measuring cylinder. Start the stopwatch and take the temperature with a thermometer. 4. Take the temperature once every three minutes for 21 minutes. 5. Test another four materials (thick foam, silver foil, bubble wrap, carpet, polystyrene packing, newspaper) in the same manner.

7 Required Practical SHC Method: 1) Mass of metal block. 2) Connect immersion heater to the power pack. Connect ammeter and voltmeter. 3) Place digital thermometer into metal block. 4) Record starting temperature. 5) Turn on power pack and start timer. 6) Calculate the power of the immersion heater. 7) Allow immersion heater to run for 10 minutes (600s), turn off power-pack. 8) Measure temperature of metal block again and record. Calculate temperature change of block. 9) Calculate amount of energy delivered by the powerpack. 10) Calculate SHC.

8 Required Practical SHC Method: 1) Measure mass of spirit burner using balance and record in table. 2) Measure 100ml of water into measuring cylinder. 3) Pour water into copper calorimeter and cover with lid. 4) Place spirit burner under a tripod with the calorimeter of water above it on gauze. 5) Place digital thermometer in water and record temperature once settled. 6) Light spirit burner and burn for two minutes. 7) Record final temperature of the water. 8) Measure mass of the spirit burner and calculate the change in mass of the fuel in the spirit burner. 9) Calculate the energy released by the fuel (mass change x energy per gram). 10) Calculate the specific heat capacity of the water.

9 Non-renewable Energy resource How it works Advantages Disadvantages Coal, oil, gas Nuclear Fuel burnt, boils water into steam, turns turbine, turns generator, generates electricity. Nuclear fission of fuels e.g. plutonium & uranium releases thermal energy, boils water into steam, turns turbine, turns generator, generates electricity. Cost-effective Large amounts of energy Fuel currently readily available Fuel costs & running costs low Reliable Can respond quickly to changes in demand. Produce no pollution when running Nuclear fuel relatively cheap High set-up costs Fuels are finite and supply of resources are running out Release CO 2 (greenhouse gas), contributes to global warming Releases SO 2, causes acid rain Coal mining spoils view. Oil spills causes damage to ecosystems and plants & animals. Transporting nuclear fuel releases pollution Disposal of radioactive waste very dangerous and difficult to dispose Equipment failure can lead to a major catastrophe e.g. Chernobyl 1986 & Fukushima Setting up and decommissioning nuclear power stations is expensive. Wind Wind turbine blades rotate in wind, gears link turbine to generator, generate electricity. Produce no pollution when running Free energy once installed 1500 wind turbines = 1 coal-fired power station Noisy Impact upon views Can be unreliable Initial costs high Renewable Tidal barrages The Sun (solar) Water waves Hydroelectricity Geothermal Bio-fuel Tides produced by gravitational pull of Sun and Moon. Tidal barrage dams built across river estuaries, as tide comes in it fills up estuary, held back by barrage. Water let through turbine at controlled speed. Generate electric currents directly from Sun s radiation. Suitable for low-energy appliances. Small wave-powered turbines are placed around the coast, move up and down, turn generator, generate electricity. Water is held in a reservoir behind dam, let out through turbine at controlled rate, turns generator, generates electricity. Energy in thermal energy stores of hot underground rocks from slow radioactive decay of radioactive elements boils water into steam, turns turbine and generator, generates electricity. Plant products / animal dung burnt in a boiler, boil water into steam, turn turbine, turn generator, generate electricity. Produce no pollution when running Minimal running costs Free energy once installed Reliable (twice a day) Produce no pollution when running Minimal running costs Free energy once installed Suitable for remote locations Produce no pollution when running Minimal running costs Free energy once installed No pollution Produce electricity immediately to respond to demand Reliable (except in times of drought No fuel costs Minimal running costs. Free energy Reliable Very little pollution Reliable Crops grow relatively quickly Carbon-neutral (carbon dioxide is taken in when plant grows and then released when plant is burnt). Prevents free access to boats Spoils view Alters habitat Height of tide is variable Doesn t work when water is same height each side of barrier (4 times a day). Require a lot of energy to manufacture Can be unreliable Doesn t generate much electricity per solar panel Disturbs seabed & habitats of marine animals Spoils view Hazard to boats Unreliable Initial costs high Initial costs high Usually require flooding of valley - loss of habitat & homes, rotting vegetation underwater releases methane & carbon dioxide. Dry reservoirs can look unsightly. Not many suitable locations Set-up costs high. Cannot respond to immediate demands Refining bio-fuels is expensive Production creates methane emissions from animals Deforestation sometimes occurs to create fields for bio-fuel crops, increasing CO 2 & methane emissions

10 ELECTRICITY Topic 2

11 Current, Charge, P.D, Resistance Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge. For current to flow; closed circuit & source of p.d. Greater resistance = less current

12 Required Practical Resistance of a Wire IV: length of wire (cm) DV: current (A), from which calculate resistance (Ω) CVs: type of wire, p.d. (V) Resistance is caused by electrons colliding with metal ions. When the length of the wire is increased, the electrons have to travel further. So the chance of collisions will increase, causing the resistance to increase.

13 Required Practical Series & Parallel Circuit Rules Type of Circuit Current P.D. Resistance Series Same Shared Total of each resistor added Parallel Shared Same Total resistance lower than smallest resistor 2+ resistors in series have to share total p.d. therefore p.d. across each resistor is lower = current = lower. Series = current same everywhere therefore total current reduced as more resistors added & total resistance increases. If one bulb blows, others of different branches stay on (current has choice of pathways. Bulbs = brighter as max. p.d. 2+ resistors in parallel = total resistance lower than smallest of resistors. Adding resistaors in parallel reduces total resistance. Both resistors have same p.d. Adding another branch, current = more choices of direction. Total current increases, therefore total resistance decreases.

14 Resistance of Components Resistors = ohmic components: directly proportional (straight line + through origin) Filament lamp = charge flows through filament, energy transfers electrically into thermal energy store then transfers by radiation. Resistance increases with T; more current = hotter = more resistance = less current. Diode = high resistance in one direction

15 Power Power = rate at which energy is transferred Power = rate at which work is done

16 Domestic Uses & Safety UK: 230V, 50Hz AC. Live wire: in at ~230V Neutral wire: current out at ~0V. Earth wire: 0V. Only carries current if fault occurs. If turned off, no current but p.d. in wire. Body (0V) forms link for current to flow to the ground from live wire (230V) = electric shock. Fire can occur in any material which creates low resistance path to the ground due to high current.

17 Energy Transfers in Everyday Appliances Amount of energy transferred/ work done depends on time switch on & power of appliance. Work is done when charge flows in circuit.

18 National Grid Insulators on pylons To 400,000V Therefore current low (wires not so hot, less energy transferred (wasted) by heating To ~230V for domestic use, current increases Demand for electricity must be predicted. Power stations often run well below max power output so spare capacity to meet high demand & to manage unexpected shut-down of other power stations. Smaller power stations kept on standby also.

19 Static Charge Rubbing insulators can transfer electrons; insulators become opposite charged, can attract. Sparking: As electric charge builds up, p.d. increases 9from 0V). When p.d. high enough electrons can move across gap- spark. Electrons can also move across from charged object to earthed conductor.

20 Electric Fields Electric field shows direction positively charged particle would move. Charged object in electric field experiences a force. Size of force is affected by strength of electric field. Closer lines = stronger field. Greater distance = less force. High p.d. causes strong electric field between charged object & earthed object. Air is normally an insulator but can act as a conductor. Strong electric field causes atoms in air to be ionised as electrons are removed. Charge can flow = spark

21 PARTICLE MODEL OF MATTER Topic 3

22 Changing State State Forces of Attraction Arrangement Potential Energy Kinetic Energy Solid Strong Fixed, regular Low Low Liquid Weaker Irregular Medium Medium Gas Almost none Separated High High

23 Required Practical Density Solid object Regular: 1) Take mass on balance. 2) Measure h, w, l with ruler, calculate volume by multiplying together. 3) Calculate mass / volume. Irregular: 1) Take mass on balance. 2) Fill eureka can to brim. Place measuring cylinder under spout. 3) Add object to can. Catch displaced water in measuring cylinder. 4) Calculate mass / volume. Liquid: 1) Place measuring cylinder on balance, zero (tare). 2) Pour 10ml into cylinder, record mass. 3) Pour another 10ml in, record total mass and volume. 4) Repeat until measuring cylinder full. 5) Calculate mass / volume. 6) Calculate average density (more precise).

24 Internal Energy Internal energy = kinetic energy + potential energy U=E k + E p The line is horizontal when boiling because The energy supplied by heating is increasing the internal energy. But instead of the temperature going up, the energy is being used to break the attractions between the molecules (the potential energy has gone up).

25 SHC- see Energy Topic

26 SLH Specific Latent Heat: The amount of energy required to change the state of one kilogram of a substance (with no change in temperature). Specific Latent Heat of Vaporisation: The amount of energy required to evaporate one kilogram of a substance (with no change in temperature). Specific Latent Heat of Fusion: The amount of energy loss required to freeze one kilogram of a substance (with no change in temperature).

27 Particles Motion in Gases & Pressure Molecules in a gas constant random motion, collide with container, exert force at right angles to surface. Outward gas pressure = sum of force exerted by all particles against walls Faster particles = more collisions with walls Increase in gas pressure. At constant V; increase T = increase p Pressure is inversely At constant T + fixed mass: proportional to volume p = 1 / V V = 1 / p Doing work (transfer of energy by force) on a gas increases internal energy = can increase temperature of gas. Pumping up bicycle tyre: Pressure increases as more molecules per area & more collisions Temperature increases as more collisions Volume increases to allow molecules to move further apart Therefore pressure decreases

28 ATOMIC STRUCTURE Topic 4

29 Atomic Structure ~ 100 different elements. Radius of around 0.1 nanometers (1x10-10 m) Nucleus has a radius of around 1x10-14 m (1/10,000 th of atom) When Who What was discovered? Beginning 19 th C John Dalton 1897 J J Thomson Plum Pudding model 1909 Rutherford / Marsden Atoms=solid spheres, different atoms=different elements Alpha particle scattering nuclear model of atom Around 1913 Niels Bohr Electrons contained in shells (calcs agreed w. obs) 1920s Rutherford & others Different no. protons = different element Different no. electrons = ion Different no. neutrons = isotope Atomic no. = p Atomic mass (Relative atomic mass (Ar)) = p+n Electronic structure = 2,8,8,2 Showed nucleus can be divided into protons 1932 James Chadwick Showed the existence of Neutrons

30 Atoms & Isotopes Isotope: same no. p. different no. n Ion: same no. p, different no. e (positive ions lost 1+ electrons from outer shell) Electrons in energy levels (shells) Electron arrangement can change: EM radiation absorbed = higher energy level Emitted EM radiation = lower energy level Radioactive decay: unstable nuclei give out radiation. Random. Activity: rate unstable nuclei decay. Measured in Becquerel (Bq). Geiger-Muller tube measures no. decays /s recorded.

31 Nuclear Equations Radioactive decay is random. Alpha radiation e.g. Beta radiation e.g. Gamma radiation: no mass, so no change

32 Half-lives The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level. Example questions: 1. A sample of cobalt-60 has an activity of 2000 Bq. What will the activity be after 10 years? Cobalt-60 has a half life of 5 years. 2. A sample of strontium-90 has an activity of 5000 Bq. After 120 years the activity has fallen to 625 Bq. What is the half life of strontium-90? 3. What is the half life of Sample A? 4. Calculate the % reduction of Sample A after 2 half lives. Radioactive isotopes have very wide range of half-lives Activity of Sample (Bq) Activity of Sample A Over 2 Minutes Time (s) 1 half life: 100 / 2 = 50 Bq 2 half lives: 50 / 2 = 25 Bq Reduction in activity = = 75 Bq (75 / 100 ) x 100 = 75% May be asked/ given as ratio

33 Radioactive Contamination Contamination = unwanted presence materials containing radioactive atoms on other materials. Avoid by wearing protective clothing & using tongs. Hazard = decay. Risk = affected by type radiation emitted. Irradiation = exposing object to radiation. Object does not become radioactive. Outside body: beta & gamma most dangerous- can penetrate body & reach organs. High levels irradiation dangerous, esp. beta & gamma. Inside body: alpha most dangerous- can t penetrate tissue so trapped inside. Contamination biggest risk. Beat & gamma can pass out & won t ionise as much.

34 Hazards & Uses of Radioactive Emissions & Background Radiation Dose = measure risk of harm to body due to exposure to radiation. Depends on type radiation. Measured in Sv (msv also used, 1000 Sv). Higher dose increased risk cancer. Background radiation = low-level, always around us. Granite releases radon gas- trapped inside houses. Detected by radon detector. Higher altitude = more exposure to cosmic rays. Nuclear industry & uranium miners = 10x normal exposure PPE inc. face mask, check-ups, radiation badges Radiographers wear lead aprons & stand behind lead screens Longer half-life = larger hazard as longer exposure.

35 Uses of Nuclear Radiation Radioactive isotopes have very wide range of half-lives Radiotherapy Lower doses radiation tend to cause minor damage without killing cell. Cells then can divide uncontrollably (mitosis) = tumour. Higher doses tend to kill cellradiation sickness if lot of body cells killed at once. Extent of harm depends on level exposure & energy + penetration (type) of radiation. Direct carefully & correct dose. Medical Tracers Internal organs can be investigated to check function, without surgery. Inject certain radioactive isotope into blood or swallow. Computer converts readings from eternal detector to display where reading is strong / weak. Use gamma / beta so radiation passes out body. Half life to be short (minutes) so radioactivity is very low & harmless within hours. Benefit & risk must be weighed up to decide best course of action.

36 Nuclear Fission & Fusion Fission Splitting large & unstable nucleus e.g. U or Pu Spontaneous fission = rare Can form chain reaction- nuclear power station Fusion 2 light nuclei collide at high speed & fuse.= into heavier nucleus. Heavier nucleus is lighter than 2 nuclei that formed it. Some mass may be converted into energy, released as radiation. Energy not transferred to kinetic energy store of product = transfers as gamma rays. Heats water, turns turbine, turns generator. Amount of energy release controlled by lowering & raising control rods- absorb neutron. Fusion currently not usable for energy generation- v. high T + p = expensive reactors.