Physics PDF Notes

Physics  Index Prefixes: 12 Tera [T] - 10 or 1,000,000,000,000 9 Giga [G] - 10 or 1,000,000,000 6 Mega [M] - 10 or 1,000,000 3 Kilo [K] - 10 or 1000 -2 Centi [c] - 10 or 0.1...

Physics  Index Prefixes: 12 Tera [T] - 10 or 1,000,000,000,000 9 Giga [G] - 10 or 1,000,000,000 6 Mega [M] - 10 or 1,000,000 3 Kilo [K] - 10 or 1000 -2 Centi [c] - 10 or 0.1 -3 Milli [m] - 10 or 0.01 -6 Micro [μ] - 10 or 0.0001 -9 Nano [n] - 10 or 0.00000001 -12 Pico [p] - 10 or 0.00000000001 -15 Atto [a] - 10 or 0.00000000000001 -18 Femto [f] - 10 or 0.0000000000000000 Note that Atomic Structure is in the chemistry document See biology for general key terms  Energy Energy cannot be created or destroyed, only stored or transferred A closed energy system is unable to exchange energy and matter with its surroundings An open energy system is able to exchange energy and matter with its surroundings Friction increases temperature as it is an exothermic process Energy stores: A higher concentration gradient between the substance and surrounding air means the substance will lost heat faster Thermal: energy stored due to a rise in temperature Only increases when objects accelerate Kinetic: energy stored in moving objects; this is influenced by temperature Chemical: energy stored in the bonds of chemical compounds Gravitational potential: energy stored as an object gets further from earth Elastic potential: energy stored due to applying force on an elastic object Magnetic: energy stored between two poles Electrostatic: energy stored between two charges Nuclear: energy stored in an atom’s nucleus Work is done whenever energy is transferred from one store to another (N) (m) Work done = Force x Distance Energy transfers: Mechanical work: a force moving an object through a distance Electrical work: charges moving due to a potential difference Heating: due to temperature difference caused electrically or chemically Radiation: energy transferred as a wave  Energy Internal energy is the total amount of kinetic and potential energy of all particles within a system; heating increases the internal energy as particles move faster Mass (kg) Kinetic energy = Velocity / speed (m/s) Gravitational field strength (9.8N/kg) Mass Change in gravitational potential energy = Change in height (m) 1N/m = 1J Spring constant (N/m) Elastic potential energy = Extension (m) Extension =Force F/K  Energy Resources - Resource Advantages Disadvantages Fossil fuels Reliable Burning these releases a huge amount of CO2 and [Oil, coal, Release a great deal of energy other pollutants [burning coal makes SO2 and diesel gas] Abundant makes NO] Extremely versatile - used for many things Non renewable - not being replenished as used Coal Cheap Releases much more pollutants More abundant Releases more smoke and soot which can cause respiratory issues Oil More versatile Harder to find Cleaner burning; less pollutants released Oil spills can damage ecosystems Won’t release soot Gas Inexpensive Methane is a potent GHG and leaks during extraction, Less polluting production and transportation Won’t release soot Renewable Can be replenished as used; will never run out Almost all UK cars run on fossil fuels so it is expensive resources Does not add any CO2 to atmosphere to change to renewable electricity Can supply energy to rural areas Can be generated in remote areas Wind/Solar Versatile in terms of size and number Relatively low cost and maintenance Unreliable as dependant on weather May spoil landscapes and occupy large areas of land Energy harnessed through movement of Unsightly and can disrupt bird flight patterns bodies of water Hydroelectric Reliable and predictable as it depends on natural Destroys habitats when dams are built and valleys are water flow flooded Long lifespan when maintained Only useful in river filled countries Tide movement drives turbines TidalMovement of seawater compressing trapped Extremely reliable Building barrages may be harmful to wildlife & costly air in a cavity on a shore to drive a turbine Huge potential to generate a lot of electricity on islands Wave Reliable with a huge potential in UK as we have Small scale and experimental so it may be costly Harnessing the natural heat of an extensive coastline; ideal for islands the earth in volcanic reigons Geothermal Generated from decaying plant / animal waste Reliable and a massive, possibly infinite potential High upfront costs & location specific to volcanic areas Biofuel Releases CO2 but is carbon neutral May push up food price if we use land to grow crops Can be used for vehicles for the fuel; only renewable if replanted Nuclear Takes thousands of years to decay Reliable and doesn’t release CO2 Will end up with radioactive nuclear waste Will last for many years Decommissioning plants is tedious and expensive  Specific Heat Capacity The specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1°C Solid block version Change in temperature (°C) Immersion heater connected to joulemeter Change in Mass Specific heat · Thermometer Insulation thermal energy capacity (J/kg°C) Joulemeter Stopwatch SHC practical: Balance Oil version 1. Place a beaker on a balance and press 0.00 2. Add oil to beaker and record mass of oil 3. Place a thermometer and an immersion heater into the oil · Joulemeter 4. Read starting temperature of the oil 5. Wrap beaker in insulating foam to reduce thermal energy transfer to surroundings 6. Connect joule-meter to immersion heater 7. Time for 30mins using something like a stopclock 8. Read number of joules of energy that passed into immersion heater 9. Read final temperature of oil 10. Calculate SHC; repeat as needed and calculate a mean 11. This experiment may be done with a solid block with two holes drilled into it for the immersion heater and thermometer Sources of inaccuracy: Thermal energy passing out of the beaker into the air; this can be reduced by using an insulator with lower thermal conductivity Not all thermal energy may have passed into the oil; this can be reduced by ensuring that immersion heater is fully submerged Incorrect reading of the thermometer; this can be reduced by using an electronic temperature probe Thermal energy may not be spread through the oil; this can be reduced by stirring the oil  Specific Latent Heat The specific latent heat is the energy needed to change the state of 1kg of a substance without changing the temperature The latent heat of fusion is the energy needed to change 1kg of a substance from solid to liquid - melting The latent heat of vaporisation is the energy needed to change 1kg of a substance from liquid to gas - boiling Specific latent heat E = M x L (J/kg) Energy Mass needed Solids: Hard to compress; particles packed close together in a regular arrangement Particles vibrating in a fixed position; they do not otherwise move Liquids: Hard to compress; particles close together but in an irregular arrangement Take the shape of their container Particles can move around each other Mass is always conserved during Gases: state changes; we do not add nor Easy to compress; particles widely spaced in an irregular take any away arrangement Spread out and take the shape of their container; particles move Heating graph Cooling graph freely and rapidly in all directions Temp Boiling Temp Condensation Melting Freezing Time (s) Time (s) Limitations of simple particle model: Assumes all particles are solid, inelastic spheres Assumes there are no forces between particles and doesn’t show the movement of particles State changes are physical changes so if they are reversed, they recover their original properties  Gas Pressure The pressure of a gas is due to the particles colliding with the walls of the container thus exerting a pressure; measured in Pascals (Pa) The particle collisions cause a force which acts at right angles to the container walls The pressure of the atmosphere is caused by air molecules colliding with the surface of the earth; there is a lower atmospheric pressure at higher altitudes as there are less air molecules higher up To increase the pressure: Increase the number of collisions per second Increase the energy of each collision by increasing its temperature To decrease the pressure: Increase the volume of the container to increase particle spacing Only true if temperature is kept constant because the particles would otherwise speed up or slow down Constant Volume (M 3) Pressure Work done on a gas: By compressing a gas we carry out work on it; we have applied a force to the gas and therefore transferred energy to the particles This increases the internal energy and therefore the temperature Pressure = Force normal to a surface Area of that surface (M 2)  Density The density of a material tells us the mass for a given volume; a higher density object will have more mass packed in its volume Mass Volume Density (kg/m 3 ) Solids are usually denser but there are exceptions such as polystyrene which has a very open structure and is full of air spaces - lack of mass Object Ruler Density of regular objects practical: 1. Determine object mass using a balance Balance E · 2. Work out the volume by using a ruler to measure side lengths; times the length by the width by the height 3. Divide the mass by the volume Irregular objects: 1. Determine object mass using a balance that is set to 0.0 2. Fill a eureka can with water and place a measuring cylinder under the spout 3. Place the object into the water causing the water to be displaced and flow out of the can through the spout 4. Measure the volume of water displaced using the measuring cylinder 5. Divide the mass by the volume; repeat as needed and calculate a mean Object Eureka can Sources of inaccuracy: Balance - Measuring cylinder Water may be spilled leading to an inaccurate volume; make sure to place the measuring cylinder directly under the spout and put the object into the can carefully There may also be a falling hazard so make sure to place it away from the edge of the desk The balance may not be accurate; make sure to set the balance to 0.0 before weighing The water might not have been fully displaced; do not rush the investigation and make sure that every drop is in the measuring cylinder  Thermal Conductivity - Thermal conductivity in buildings: Modern houses are build from two layers: external brick and internal breezeblock; between the walls there is a cavity The thermal conductivity of walls built like this is fairly high which is a problem as a lot of thermal energy can transfer out of the house; this means more money is spent on heating To combat this, builders pack the cavity with an insulating material with very low thermal conductivity; this is called cavity wall insulation Thermal energy can also escape through windows; this is reduced by double glazed windows which have low thermal conductivity as they are too narrow for air to travel up and down concurrently which reduces convection currents thus reduces energy transfer Thermal energy can also escape through the roof; this is reduced by loft insulation Building a house with thick walls reduces the rate of thermal energy transfer Cardboard lid · Thermometer Kettle Thermal insulators practical: Stopwatch Beakers with an insulating 1. Place a small beaker inside a large beaker material in between them 2. Use a kettle to boil some water and try to aim for consistency each time; make sure to be safe and not scald skin and don’t overfill 3. Transfer 80cm 3 of hot water into the small beaker; make sure not to knock beaker off the desk and place it away from the edge 4. Use a piece of cardboard with a small hole in it as a lid for the large beaker 5. Place a thermometer through hole in the lid; the bulb must be in water 6. Record starting temperature of the water and start a stopwatch 7. Record the water temperature every 3 mins for 15 mins [record 5 times] 8. Repeat as needed and calculate a mean 9. Repeat steps 1-8 using same volume of hot water but with an insulating material to fill the gap between the two beakers and test a range of materials; insulating material must be the same mass each time 10. Record a results table and plot a cooling curve from the results  Thermal Conductivity With newspaper: 1. Start with a beaker containing 80cm 3 hot water 2. Measure water temperature every 3 mins for 15 mins 3. Repeat as needed and calculate a mean 4. Repeat steps 1-3 add add 2 layers of newspaper around the beaker 5. Repeat steps 1-4 2 more times and add 2 more layers each time Sources of inaccuracy: Initial temperature of water may not be consistent each time; this is reduced by paying attention to how long its boiling Possible human error when transferring water from kettle to beaker; this is reduced by pouring the water slowly Incorrect timekeeping; this is reduced by paying close attention to the stopwatch Insulating materials may not be the same mass each time; this is reduced by weighing the materials on a balance correctly  Efficiency Useful output of energy transfer Efficiency = - Total input Useful power output Efficiency = Total power input - Efficiency can be increased by: If cooking, using a pan with a wider base and a lid Placing a heating element in cooking devices to reduce energy used by heating up the base of the pan Using plastic walls and lids to reduce heat conducted Mechanical devices may be lubricated to reduce friction Insulation may be used to reduce waste energy to surroundings Electricity Power is the rate of energy transfer or the rate at which work is done measured in Watts or J/s Power = Energy transferred Time Power = Work done Time Power = Voltage x Current Power = Current x Resistance 2 Appliances that utilise electrical energy: Blender Oven Fan Electrical energy transferred into kinetic energy of electric motors - small amount of thermal waste energy generated due to friction in motors Toaster Refrigerator Lamp Electrical energy transferred into light energy with some waste thermal energy Kettle Electrical energy transferred into thermal energy Hairdryer Electrical energy transferred into the kinetic energy of the motors and some thermal energy Iron Washing machine  Circuits Components: High resistance in dark conditions - Thin wire that breaks circuit when current gets too high Cell - Fuse - · Low resistance in light conditions Light dependant resistor [LDR] - semiconductor ↑ - - J Resistance can be changed by moving the position on a slider Battery Voltmeter Variable resistor - - The resistance of a thermistor decreases if the temperature increases Filament bulb / lamp Arrow - direction Ammeter Thermistor - semiconductor of conventional - current Allows current to flow in only one direction with a very high resistance in the reverse direction Open switch Diode - semiconductor - - Diode that gives off light when current flows through; extremely energy efficient source of light Closed switch Light emitting diode [LED] - semiconductor = Resistor Potential difference is the force or pressure that drives the flow of current; a potential difference of 0 volts means there is no force to drive the movement of electrons and thus no work is done as they have no kinetic energy Whenever charge flows in a circuit, work is done due to the energy transfer it accompanies Current is the rate of flow of charge - an electrical current is a flow of electric charge through a conductor Cell has a store of chemical energy which is transferred to electrical energy and carried by electrons passing in and out Current flows from negative end of cell to positive end; electrons carry energy from the cell to pass it onto the components Note that current is usually drawn the opposite jj way called the ‘conventional current’ [positive to negative] as it was originally thought to have Carrying less energy than flown in this direction when they left the negative end as it was expended More energy causes more work to be done per coulomb onto components of charge and thus a higher voltage; this essentially means there is more potential for energy transfer or more energy available for transfer Time Potential Electrical energy transferred to light and thermal energy difference Current (amperes/A) Charge (coulombs/C) Energy Charge (volts/V) Series circuits: Man Man I Current is never used up in a circuit * J * 0 1 A. The total P.D between the i two lamps is the same as t the P.D across the cell Lights are dimmer as energy is shared between the bulbs and less Electrons transferring 9J of Voltmeter goes in parallel electrical energy is transferred to one lamp at a time energy per coulomb of charge Ammeter goes in series +.. J J Two cells One of the cells is in the wrong direction so the voltages cancel out  Circuits Parallel circuits: · P.D across each component is the same Current splits; some passes through both branches at a time and the current in the branches adds up to the total current leaving the cell - The resistance tells us the potential difference required to drive a current through a component, i.e, how much energy is required to push a coulomb of charge through Resistance in series circuits add together as current has to pass through all resistors and cannot bypass any; you could therefore replace multiple resistors in a series circuit with one that is their sum and provide equivalent resistance The total resistance of two resistors in parallel is less than the lowest resistance Resistance (ohms/Ω ) P.D B o More pathways for current to take meaning more total current will flow through the circuit at a time; if current increases and the P.D remains the same, the total resistance must have decreased -or " lose " Ther Current Electrons collide with metal ions and collisions slow down the flow of current causing resistance which means more energy is required to drive current through [this is only true if the P.D is kept constant]; a higher resistance means the rate of energy conversion across components is lower as Metal wire less current is going through at a time - Filament lamp: Resistors: As the P.D increases, the current also - Da increases telling us the resistance is J The atoms in the filament vibrate more constant causing electrons to collide more with the ions The filament heats up causing an increase in The current moving through the filament lamp is not directly The resistance will resistance; this means more only stay constant if The current moving through the resistor energy is needed to push proportional to the P.D across the lamp the temperature is is directly proportional to the P.D across current through the filament constant because a the resistor; this causes a constant higher temperature resistance because R=V/I causes more electron collisions / ↓ A filament is a very fine wire with very ↓ tight coils which gets extremely hot when This kind of resistor is called an current passes through; this causes it to ohmic conductor and it is often used emit light to control the P.D across other components Bulb getting hot " As the P.D increases, the current no longer increases as much which tells us the resistance is increasing (R= V/I)  Circuits Diodes: Cell switched so current flows in the opposite direction -joj ↓ ↓ ↓ · Will not flow after here due to a very high resistance in the reverse direction; this is useful for controlling the flow of - current Current in the forward direction: low resistance Current in the reverse direction: very high resistance Sudden rise at a certain value of forward voltage: threshold voltage / knee voltage Light dependant resistors: Low light intensity - high resistance 8" - J If Resistance Light intensity Useful to detect light, e.g, turning a device screen off in dark environments to save energy, garden lamps, street lights High light intensity - low resistance rig 8 J Light conditions Dark conditions (held to someone’s ear, in pocket, etc) Lamp to backlight screen Lamp becomes dim Wi - an ↳a Low resistance so low P.D High resistance so high P.D Thermistors: 8" - Low temperature - high resistance J Useful as thermostats to turn appliances on or off Resistance depending on the temperature Useful in incubators to control the environment High temperature - low resistance ↓ Temperature 8 Mi Computer in cool conditions Under cool conditions the thermistor has a high resistance Wan Cooling fan Less electrical energy available so fan is at a low speed J Win Computer in hot conditions: overheating Under hot conditions, the thermistor has a low resistance Cooling fan ar More electrical energy available so the fan is at a high speed  Circuits I / V characteristics of components practical: 1. Set up a circuit with a battery, an ammeter, a resistor, a variable resistor and a voltmeter; connect the voltmeter in parallel to the resistor 2. Use the voltmeter to read the P.D across the resistor; record this value 3. Use the ammeter to read the current through the resistor; record this value 4. Adjust the variable resistor and record the new readings on the ammeter and the voltmeter; do this several times to gather a range of readings 5. Switch the direction of the battery; continue taking several readings of the ammeter and voltmeter, both of which should now have negative values 6. Repeat as needed and calculate a mean, plotting an IV graph from this mean 7. Repeat the steps 1 to 6 using a filament lamp in place of the resistor 8. Repeat steps 1 to 6 using a diode in place of the resistor and add an extra resistor in series as to keep the current low and protect the diode; they are very easily damaged by high currents - use a milliammeter as well due to this [sensitive ammeter] Sources of inaccuracy: Heating effects Connection errors between components Human error when reading values D ⑰ Battery Ammeter Variable Voltmeter resistor Resistor Filament lamp D ⑰ Switched battery Milliammeter direction Extra Diode resistor  Circuits Resistance practical: 1. Gather a battery, an ammeter and a voltmeter 2. Attach a wire to a meter ruler using tape 3. Connect desired amount of the wire to the circuit, made using the aforementioned apparatus, using crocodile clips; make sure to connect the voltmeter in parallel to the wire 4. Lengthen or shorten as needed using the crocodile clips and note down values for the resistance by dividing the potential difference values by the current values 5. Repeat as needed and calculate a mean Sources of inaccuracy: Zero error: a reading on a measuring instrument when the value should be zero which is a systematic error caused by the equipment that cannot be reduced by repeating the investigation - ensure to subtract the zero error from all readings Heating effects: if the temperature of the wire increases then the resistance will also increase - can be reduced by using a low P.D which will keep the current low or only turning on the current when taking a reading and switching it off otherwise + 7 · Wire Voltmeter Ammeter Resistance The resistance of the wire is directly proportional to its length Crocodile clips Ruler Length of wire (m) A direct current [DC] is one that only flows in one direction An alternating current [AC] is one that constantly switches direction; in the UK this is 50 times per second meaning it has a frequency of 50Hz It has a potential difference of around 230V An alternating current makes it easier to use a transformer to increase or decrease the One peak to the next peak = one complete cycle potential difference 1 Frequency is the number of cycles in 1 second Hertz (Hz) Frequency = 1/0.02 = 50Hz Frequency = Time difference between two peaks 0.02 seconds = the time take for current to 230 change direction and then change back once P.D 0. 01 0 02. 0. 03 (5)  Transformers * Iron core; this is easily Same number of turns means the P.D is the same in both coils; magnetised so increases the this is only true if the transformer is 100% efficient but assume strength of the magnetic field it is Only works with AC because it needs a changing magnetic field to induce a potential difference AC Primary coil Secondary coil Power must be conserved so the power of the primary coil = the power of Generates a changing magnetic field as it flows through Completely separate; there is no way for electrical the secondary coil; only true if the transformer is 100% efficient the primary coil which is transmitted along the iron core current to pass directly from one coil to another to pass it through the secondary coil; this induces a P.D * More turns than the primary coil [twice as many] so the P.D induced will by 2x greater; step-up transformer * P.D in the primary coil More turns than the secondary coil so the P.D in the secondary coil will be smaller; step-down transformer P.D in the P.D in the primary coil secondary coil V N Number of turns in the primary coil IV=IV PPSS V=N P.D in the secondary coil Number of turns in the secondary coil Current in the primary coil Current in the secondary coil  Mains Electricity Mains electricity is an alternating current; electrical appliances are connected to the mains supply · using a three cord cable: Safety wire at 0V which provides a low resistance path for charge to get to the ground to stop appliance becoming live and this needs to touch the casing of the appliance to access the charge; a low resistance means high amounts of current can flow through The metal case attached to the earth wire; if a fault occurs with the live wire that poses a risk of current flowing into an outside source such as a person [for example through it coming into contact with the case and it thus becoming electrified], this charge will instead go through the earth wire into the earth to prevent electrical shock - This large current flowing through the live wire also heats up and melts the fuse which breaks the circuit Carries the alternating P.D from the supply (230V) - commented to a fuse in the plug and is fatal if touched Completes circuit and takes The potential difference between the earth and the neutral wire is 0V current back to the source; it has a P.D of 0V Because of the large potential difference of 230V between the live and the earth wire, a large current would be created if they were connected together and this could cause a fire or even electrocution; electricians switch off the mains supply when working because humans have a P.D of 0V which can create a large current if we were to come into contact with a live wire, a surge of current would flow through us and electrocute us Even if a device is switched off, but the mains supply is on, the live wire can still cause an electric shock because it is connected to mains, and even If the earth wire didn’t have access to the casing, the charge would instead flow through the person as they would provide a if a switch is switched off and thus open in the mains supply, if you touch it, you may complete a circuit between the live wire and the earth and pathway for current to get to the earth instead of the earth wire; this person would be electrocuted get electrocuted Each wire is made of copper which is a good electrical conductor They have plastic PVC insulation over the wire to preserve the material against environmental threats and prevent the charge from coming into contact with other conductors such as the other wires The National Grid & High voltage distribution cables 3 Power station Voltage increased to 400kV through the step-up transformer to decrease Step-up transformer current; this means less heat is generated and therefore less energy is Step-down transformer which increases P.D which decreases P.D wasted which increases the efficiency 2 4 Electricity generated at 25kV Voltage decreased to 230v for the safety of consumers The national grid is a system of transformers and cables: 1. Step-up transformers increase the potential difference which reduces energy lost by heating in the distribution cables and this increases efficiency 2. Step down transformers reduce the potential difference before the electricity passes to homes  Static Electricity 1. Electrons cannot move through insulators; when insulating materials rub against each other, they may become electrically charged by friction 2. The negative electrons can be ‘rubbed off ’ one material onto the other as they gain enough energy to leave the atom through this friction 3. The material that gains electrons becomes negatively charged and the material that loses electrons becomes positively charged; as the electrons cannot move, the charge remains static 4. This creates a difference in charge between the material and the 0V earth which increases as the material is further charged 5. A spark can occur as the electrons ionise the air and jump from the charged surface to the earth Non contact force Electric Fields Arrows show the direction of force when a positive object is brought nearby [this shows repulsion]; if objects are brought closer together, the force strengthens Attraction Field lines strengthen as proton number increases; these have to be perpendicular to the surface When touching a Van de Graaff generator, you become positively charged; 1 this causes your hair to spike up as each hair is now positively charged and thus the strands repel each other and move apart S i in  Radioactivity Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons Some of these isotopes have an unstable nucleus; they are called radionuclides; to become stable, the nucleus gives out radiation and this process is called radioactive decay Radioactive decay is a totally random and arbitrary process There are three types of radioactive decay: alpha, beta, gamma The activity is the rate at which a source of unstable nuclei decay; it is measured in becquerels [Bq] Radioactivity is the rate at which a sample emits radiation 1 Bq is equal to 1 decay per second To measure the activity of a source, we can use a Geiger-Muller tube; the count-rate is the number of decays recorded each second by a detector like the Geiger-Muller tube and this is not the same as activity due to external sources that may influence it Alpha decay is the decay of an isotope into another element due to it ejecting an alpha particle [helium nucleus] and thus losing 2 protons; alpha particles consist of 2 protons and 2 neutrons Mass number decreases by 4 as it lost 2 protons and 2 neutrons 235 231 4 92 U → 90 Th + 2 α Beta decay is the decay of an isotope into another element due to a neutron in its nucleus splitting into a proton and electron; a beta particle is the aforementioned electron which is ejected from the nucleus at a very high speed - it turns into another element as it gains a proton The proton number changes as one was gained however the mass number remains the same as a neutron was split and thus no longer a neutron 14 6C → 147 N +-10β Gamma radiation is a type of electromagnetic radiation from the nucleus; this comes in the form of There is no element change so the atomic number and mass do not change a wave instead of a particle Because these neutrons are so unstable, they usually decay into a proton and electron within minutes Neutron radiation is a form of unstable radiation presented as free neutrons; neutron radiation is not directly ionising as it has no charge and is thus unaffected by electrostatic forces meaning it cannot directly interact with electrons  Radioactivity Properties of alpha, beta and gamma radiation III Property Alpha [α] Beta [β] Gamma [γ] Range in air They are large and can They are small but can Gamma radiation can It is safe to use alpha particles in consumer products such as smoke alarms because their low penetrating power means they will be stopped by the material of the product / other factors before they come in contact with a person; this is travel around 5cm in air reach around 15cm in air travel several metres in also useful as a change in count rate would be detected if the alpha particles came into contact with a smoke barrier between the source and the detector and thus couldn’t reach the detector in the smoke alarm before they collide with air before stopping air before stopping Radiation sources in a smoke alarm should have a long half life so that the particles and stop count rate stays approximately constant regarding the detector and the activation threshold for the smoke alarm isn’t reached unnecessarily meaning that the smoke alarm won’t have to be replaced too much Penetrating power Stopped by a single sheet Stopped by a few Mostly stopped by Ionising power links to penetrating power as large particles that keep colliding with air atoms can’t penetrate very many things of paper millimetres of aluminium several centimetres of lead Ionising power Very strong ionising power Quite strong ionising Weak ionising power The power of these types of radiation to form ions out of This is why they have a small range in air: they atoms by colliding with them and making them lose easily ionise the atoms in the air meaning they lose kinetic energy as they collide and eventually stop power electrons They are large and so transfer a lot of energy when they collide with atoms which gives those atoms enough energy for an electron to be ejected and to become ions The percentage of nuclei from the original sample goes from 100% to 50% to 25% to 12.5% to 6.25% to 3.125% to ~1.6% to ~0.8% to ~0.4% etc 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; this means the current value keeps halving Because the activity of a sample is so unpredictable and spontaneous, scientists determine the half life instead If an isotope has a short half life, that means it takes less time for half the nuclei in a sample of it to decay The half life is also the time it takes for the count rate or activity of a sample containing an isotope to fall to half its initial level Example Q: A radioactive isotope has a half-life of 15 / 1000 750 days and an initial count rate of 200 counts per second. The time it takes for half the number of nuclei in the sample to Number of Determine the count rate after 45 days. undecayed nuclei decay is 10 minutes [1000 to 500 to 250 to 125] - the half 500 life is 10 minutes 250 45/15 = 3 meaning it will go through 3 half lives 0 ((200 / 2) / 2) / 2 = 25 0 10 20 30 40 50 60 Time [minutes]  Radioactivity Irradiation is exposing an object to nuclear radiation [alpha, beta, gamma or neutron] Some medical equipment can be sterilised by gamma radiation; they are placed in sealed plastic wrappers to prevent bacteria entering and are then placed near a radioactive isotope that emits gamma radiation [a lead shield is in place to protect the workers] The lead shield is then withdrawn to allow the gamma radiation to irradiate the object which kills any bacteria present The object does not become radioactive as it does not come into contact with the actual radioactive isotope, only the radiation Exposure to ionising radiation [radiation with the power to ionise atoms] can increase the risk of cancer in humans People who work with radioactive isotopes need to take precautions: Gloves can protect against alpha radiation, however, as beta and gamma radiation are more penetrating, they need to be shielded against by a lead apron With high levels of radiation, a lead apron may not be enough so Shielding some instances may require lead walls and lead screening [such as work with nuclear fuel] A radiation monitor can measure how much radiation has been Monitoring received - this does not stop radiation but it can determine if someone should keep working with radioactive isotopes depending on how much radiation they have already received Non medical equipment can also be sterilised by gamma radiation such as foods, consumer products and smoke detectors, however, consumers have a right to know if their product has been irradiated as the public may correlate irradiation with cancer Bacteria in consumer products can be irradiated and destroyed which increases the shelf life of the product  Radioactivity Radioactive contamination is when unwanted radioactive isotopes end up on other materials, thus contaminating them This is hazardous as the radioactive atoms decay and emit ionising radiation Alpha radiation is strongly ionising but easily stopped by dead cells on the skin surface, however, alpha emitting isotopes can be dangerous if inhaled or swallowed; these particles can now crash into living cells and damage DNA Beta radiation is quite ionising but it can penetrate skin into the body which poses a risk due to probable cell damage Gamma radiation is weakly ionising and it can easily penetrate the body so it is likely to pass through, however, there is a risk of cell damage if it stays in the body Over the years, scientists have explored the effects of radiation on humans It is important that these studies are published and then shared with other scientists to be peer reviewed Some extra uses of radioactivity: Leaks in underground oil pipes can be found by injecting a radioactive isotope into the oil supply and using a radiation detector to detect the count rate across the ground; the count rate will be higher where the leak is as there would be a build up of the radioactive isotope around / at that spot  Radioactivity Nuclear radiation in medicine: A tracer is a radioactive isotope that can be used to track the movement of substances around the body; medical tracers are usually made on site for quick and easy access to them Exploring internal organs using a tracer: To check the function of the thyroid gland, a patient drinks a solution of radioactive iodine I-123; the thyroid gland [found in the neck] works by absorbing iodine and using it to make hormones This radioactive isotope of iodine emits gamma radiation which passes out the body and can be detected ; if the scan shows that the thyroid has absorbed too much or too little iodine, and the doctor can then use this to diagnose the patient’s condition Bone scans use radioactive isotopes [usually Tc-99] that emit gamma or beta radiation to visualise damage caused by arthritis or to detect tumours The isotope I-125 can be injected into a patient to check kidney function by observing as to whether it is excreted or if it builds up [indicating bad kidney function] The tracer must emit radiation that can pass out of the body and be detected [gamma or beta radiation]; alpha particles would not pass out of the body; the tracer must also not be strongly ionising to minimise damage to body tissue The tracer must not decay into another radioactive isotope to regulate the dosage and half life of radiation given to the patient and the tracer must also have a short half life so it is not present in the body for a long period and won’t cause significant damage to cells and tissues and so that conditions can be detected quickly and relatively safely Controlling or destroying unwanted tissue: Certain cancers can be destroyed using ionising radiation; this process is called radiotherapy Gamma rays can pass into the body and destroy a tumour for example, however, healthy tissue may also be damaged as the radiation passes through the body This be done to target cancer in a person’s head and so a source of gamma radiation will move in a circle to minimise damage to healthy tissue by giving healthy cells a lower dose at a time whilst still directly targeting the cancer Radioactive rods can be inserted into the source of the cancer which targets the radiation very precisely to the tumour causing less damage to healthy tissue Cancer cells are more likely to die from radiation exposure than normal cells during radiotherapy as they are weaker at repairing themselves after DNA damage by radiation  Radioactivity Background radiation is radiation that is present all around in the environment; this causes radiation detectors like a Geiger-Muller tube to go off constantly due to the constant decays occuring Certain rocks are radioactive such as granite - this can be a major source of background radiation in parts of the UK such as Cornwall Cosmic rays from space are also a source of background radiation; these are very high energy particles which travel through space and crash into earth’s atmosphere and one source of these are supernovae Fall out from nuclear weapons testing has released radioactive isotopes into the environment for decades - this is a man made source Radioactive isotopes can also be released by accidents at nuclear power stations; this is also a man made source Exposure to background radiation is influenced by location and occupation People in regions with large amounts of granite experience more background radiation than others Cabin crew and airline pilots will experience more cosmic background radiation than others which means they have to limit their number of flights per year The dose of radiation is measured in sieverts [Sv] - one millisievert [mSv] is 1/1000 of a sievert Sources of background radiation: Cosmic rays - 10% Rocks and building materials - 15% Food - 11% Medical equipment - 13% Radon gas - 50% Other sources - 1%  Nuclear Fission and Fusion Nuclear fission: Some elements have large and unstable nuclei such as certain isotopes or uranium and plutonium In fission, the nucleus of these elements split; this can happen spontaneously, however, this is quite rare The nucleus usually first has to absorb a neutron for fission to occur In a short amount of time, a huge amount of uranium nuclei have undergone fission and a huge amount of energy has been released; this is called a chain reaction and the diagram below shows this Uranium nucleus U Neutron U When a uranium nucleus absorbs a neutron, a fission reaction is triggered and the nucleus splits into two daughter nuclei, The neutrons emitted can now be U roughly equal in size - it also emits two or three neutrons as well as gamma radiation - energy is also released and all of absorbed by more uranium nuclei and the fission products have kinetic energy trigger fission again Scientists can control a fission chain reaction and use it to release energy in a nuclear reactor; this can be used to generate electricity, however, gamma radiation is a byproduct of fission which has a high penetrating power that can reach consumers and cause acute exposure effects to humans, animals and the environment Moreover, this process requires very expensive equipment and creates nuclear waste The explosion in a nuclear weapon is caused by an uncontrolled fission chain reaction; this can be done by humans which is dangerous  Nuclear Fission and Fusion Nuclear fusion: Two light nuclei such as hydrogen are joined to form a heavier nucleus; this is not a chain reaction Some of the mass of the nuclei can be converted into energy which is released as radiation; much more energy is released in fusion than fission Fusion occurs naturally in stars, such as the sun, to release energy Developing nuclear fusion power stations would allow for another source of energy to be available and would thus increase the electrical supply The fuel that would be used in a fusion reactor is easier to obtain than fission fuel, would be available in large amounts and wouldn’t release gamma radiation which would reduce environmental damage  Magnetism A magnetic field is a region around a magnet where a [non-contact] force acts on another magnet or on a magnetic material; the field is strongest at the poles of a magnet The strength of a magnetic field depends on the distance from the magnet; the force experienced will be smaller if the magnet or magnetic material is further away from the magnet and vice versa When you bring two magnets close together, they exert a force on each other in which like poles will repel each other [which forces the magnets apart] and the unlike poles attract each other The direction of a magnetic field can be found using a compass: a magnetic compass contains a small bar magnet, and this compass can be placed at different points around the north pole of a larger bar magnet to plot the magnetic field lines from north to south To do this, draw a cross at the north pole of the compass after you’ve placed it near the north pole of the bar magnet and subsequently move the compass so that the south pole of it - is on the aforesaid cross and continue plotting Continue this at different starting points near the north pole and connect the crosses at the end The direction of the field lines are always - shown by using an arrow and they always run from north to south - S The earth has its own magnetic field due to its iron core; this is shown by the fact that a magnetic compass, held away from any external magnets, will always point in the north-south direction due to the force on it by earth’s poles  Magnetism The four types of magnetic material are iron, steel, cobalt and nickel and they can all be made into induced or permanent magnets Permanent magnets produce their own magnetic field A bar magnet is an example of a permanent magnet Two permanent magnets brought close to each other will attract or repel each other depending on the poles they face respectively Induced magnets become magnets when placed in a magnetic field If you place a permanent magnet near a magnetic material, the said material will become a magnet; if the permanent magnet is taken away, the induced magnets will lose most or all of their magnetism Induced magnetism always causes a force of attraction meaning that induced magnets are never repelled - When a current flows through a conducting wire, a magnetic field is produced around the wire; this can be proved by using a compass whereby the compass will point in the north-south direction when the current is off to line up with the earth’s magnetic field and will otherwise deflect when the current is turned on The direction of the magnetic field can be found using the right hand grip rule J Place your right hand so that your Right hand grip rule: · thumb is pointing in the direction of · the conventional current, so that your Direction of magnetic field fingers point in the direction of the magnetic field Switched cell Direction of conventional current The strength of a magnetic field depends on the size of the current meaning that a larger current will produce a stronger magnetic field The magnetic field is also strongest closer to the wire so, if you move away from the wire, the magnetic field strength will decrease Changing the direction of the current changes the direction of the magnetic field; a compass placed near this wire would deflect in the opposite direction to before  Magnetism Another way to increase the strength of a magnetic field in a wire carrying an electric current is to coil the wire; this shape is called a solenoid, and the magnetic field increases as the number of turns in the solenoid increases This will further increase if a piece of iron is placed inside the solenoid; a solenoid containing an iron core is called an electromagnet & When the current is turned on, we get a strong and uniform magnetic field inside the solenoid; the magnetic field around the solenoid looks similar to that of a bar magnet Electromagnets are useful because we can change the strength of the magnetic field by changing the size of the current and we can also switch electromagnets on and off - Electromagnetic devices: Relays: A relay contains two separate circuits, with a low voltage circuit and a high voltage circuit Low voltage circuit turned off Low voltage circuit turned on T T High voltage applicance High voltage applicance High High voltage voltage power power supply This keeps the contacts apart so that the supply high voltage circuit stays off Two metal contacts that replace the switch Spring Spring · Iron block Contacts · Iron block Contacts · · Magnetic field attracts the iron block, which Safe to be turned Low Electromagnet Low Electromagnet causes the spring to extend and the contacts to voltage voltage close, thereby switching on the high voltage on and off power power supply No current is flowing through this which supply circuit means no magnetic field is induced Doorbells: Clapper Clapper Bell Bell The iron contact is attracted towards the magnetic field, which causes the attached clapper to hit the bell; this breaks the circuit at the same time which impedes the flow of current and therefore stops the magnetic field, causing the iron core to spring back to its original position for this process to repeat again &