P2 Revision

1. P2 Revision

2. Speed and Velocity SPEED – how fast your going VELOCITY – how fast you going and the direction S = Displacement measured in metres (m) V = Velocity measured in m/s T = Time measured in seconds (s) S V x T EXAMPLE; A cat skulks 20 metres in 35 seconds Find a) average speed b) how long it takes to skulk 75m V = s/t = 20/35 = 0.5714 = 0.57m/s T = s/v = 75/0.5714 = 131s = 2mins 11s

3. Acceleration Acceleration is how quickly the velocity is changing V = final velocity measured in m/s U = initial velocity measured in m/s A = acceleration measured in m/s² T = Time taken measured in seconds (s) (v-u) A x T EXAMPLE; A skulking cat accelerated from 2m/s to 6m/s in 5.6s. Find its acceleration ANSWER; A = (v-u)/t (6-2)/5.6 = 4/5.6 = 0.71 m/s²

4. Velocity Time Graphs • GRADIENT = ACCELERATION • Flat sections represent a steady speed • Steeper the graph, the greater the acceleration/deceleration • Uphill sections (/) are acceleration • Downhill sections (\) are deceleration • The area under any section of the graph = distance travelled in that time • A curve means changing acceleration CALCULATING; • Acceleration = gradient = vertical change horizontal change • Velocity = read off the value from the velocity axis • Distance travelled = in any time interval is equal to the area under the graph

5. Forces Six different forces; • Gravity/Weight – always acting straight downwards • Reaction force from a surface – acting straight upwards • Thrust/Push/Pull due to an engine speeding up something • Drag/Air Resistance/Friction – slowing something down • Lift due to an aeroplane wing • Tension in a rope or cable There are five different force diagrams; • STATIONARY OBJECT – All forces in balance Reaction • Gravity/Weight is acting downwards • Reaction Force pushing up • So all forces are balanced • Without reaction force it would accelerate downwards due to the pull of gravity • The 2 horizontal forces must be equal and opposite (or zero) otherwise the object will accelerate sideways Weight/Gravity

6. Reaction To move with a steady speed the forces must be in balance. If there is an unbalanced force then you get acceleration, not a steady speed. 2) STEADY HORIZONTAL VELOCITY – All forces balanced 3)STEADY VERTICAL VELOCITY – All forces balanced Thrust Drag Weight Drag Weight

7. You only get acceleration with an overall resultant (unbalanced) force The bigger this unbalanced force is the greater the acceleration. Note; that the forces in the other direction are still balanced. So if the acceleration is vertical, the horizontal forces are still balanced acceleration 4) HORIZONTAL Acceleration – unbalanced forces 5) VERTICLE ACCELERATION – unbalanced forces acceleration

8. Friction Forces FRICTION SLOWS THINGS DOWN; • If an object has no force it will always slow down and stop because of friction • Friction always acts in the opposite direction to movement • To travel at a steady speed, the driving force needs to balance the frictional forces • You get friction between 2 surfaces in contact or when a object pas through a fluid (drag) RESISTANCE/DRAG FROM FUILDS/AIR/LIQUID; • The most important factor in reducing drag in fluids is keeping the shape of the object streamlined, like boat hulls. The opposite extreme is a parachute which is bout high drag. DRAG INCREASES AS THE SPEED INCREASES; Resistance from fluids increases with speed. A car has much more friction to work against when travelling at 70mph compared to 30mph. So t 70mph the engine has to work much harder to maintain a steady speed. Therefore it uses more petrol.

9. Terminal Velocity When the downward force of gravity/weight equals the upward force of the air resistance and the objects stops accelerating because the forces are balanced and travels at a constant speed The terminal velocity of any object depends on the drag in comparison to its weight. The drag depends on its shape and area. So a skydiver covers a small area, he will reach terminal velocity at around 120mph. Where as a skydiver with an open parachute will reach terminal velocity at 15mph – a much safer speed to hit the ground. This is due to the fact there is more air resistance .

10. Forces and Acceleration If the forces on an object are all BALANCED, then it’ll keep moving at the SAME SPEED in the SAME DIRECTION. (if it starts off still it will stay still) • When something is moving at a constant speed without changing direction – all the forces must be balanced • You NEVER need a constant overall force to keep them moving • To keep a steady speed there must be NO RESULTANT FORCE If there is an UNBALANCED FORCE, then the object will ACCELERATE in the direction of the force. The size of the acceleration is decided by the formula: F = ma • An unbalanced force will always produce acceleration/deceleration • This acceleration can take 5 different forms: starting, stopping, speeding up, slowing down and changing direction • On a force diagram the arrows will be unequal

11. F F = Resultant force measured in Newton's (N) M = Mass measured in kg A = Acceleration measured in m/s² M x A The overall UNBALANCED FORCE is often called the RESULTANT FORCE • The bigger the force - the greater the acceleration/deceleration • The bigger the mass - the smaller the acceleration • To get a big mass to accelerate as fast as a small mass, it needs a bigger force. Just think about pushing a heavy shopping trolley EXAMPLE: What force is needed too accelerate a mass of 12kg at 5m/s² ANSWER: F = ma F = 12 x 5 = 60N

12. Reaction Forces If object A EXERTS A FORCE on object B then object B exerts THE EXACT OPPOSITE FORCE on object A! • That means if you push against a wall, the wall will push back against you just as hard. And as soon as you stop pushing, so does the wall. If you think about it, there must be an opposing force when you lean against a wall – other you and the wall would fall over • If you pull a cart, whatever force you exert on the rope, the rope exerts the exact opposite pull on you. • If you put a book on a table, the weight of the book acts downwards on the table and the table exerts an equal and opposite force upwards on the book WHENEVER AN OBJECT IS ON A HORIONTAL SURFCE THERE’LL ALWAYS BE A RACTION FORCE PUSHING UPWARDS, SUPPORTING THE OBJECT. THE TOTAL REACTION FORCE WILL BE EQUAL AND OPPOSITE TO THE WEIGHT

13. Stopping Distances The distance it takes to stop a car is divided into thinking and braking distance THINKING DISTANCE; It is affected by three main factors; • How fast you’re going – whatever your reaction time, the faster you’re going, the further you’ll go • How dopey you are – affected by tiredness, drugs, alcohol and old age • How bad the visibility is – lashing rain and oncoming lights etc make hazard harder to spot BRAKING DISTANCE; It is affected by four main factors; • How fast your going – the faster your going, the further it takes to stop • How heavily loaded the vehicle is – with the same brakes, a heavily loaded vehicle takes longer to stop. A car won’t stop as quick when its full of people and luggage and lowing a caravan • How good your brakes are – all brakes must be checked and maintained regularly. Worn/faulty brakes will let you down catastrophically • How good the grip is – this depends on three things, road surface, weather + tyres

14. SPEED LIMITS; they are so important because of how long it takes cars the break. Leaves and diesel spills and much on the road are serious hazards because they’re unexpected. Wet/icy roads are always much more slippy than dry roads, but often you only discover this when you try to brake hard! Tyres should have a minimum tread depth of 1.6mm. This is essential for getting rid of the water in wet conditions. Without tread, a tyre would simply ride on a layer of water and skid very easily. This is called aquaplaning.

15. Momentum Momentum = Mass x Velocity • The greater the mass and velocity of an object the more momentum • Momentum is a vector quantity – it has size and direction (like velocity) Force Acting = Change in Momentum Time taken for change to happen • When a force acts on an object, it causes a change in momentum • A larger force = faster change of momentum (& greater acceleration) m/s Kg m/s kg Kg m/s Newton's s

16. Car Safety If someone's momentum changes very quickly, like in a car crash the forces on the body will be very large – and would cause injury. This is why cars are designed to slow people down over a longer time when they have a crash – the longer it takes for a change in momentum – the smaller the force. SAFETY FEATURES; • CRUMPLE ZONES – crumple on impact, increasing the time taken for the car to stop. • SEAT BELTS – stretch slightly increasing the time taken for the wearer to stop. This reduces the forces acting on the chest. Seat belts reduce the number of deaths in car crashes by 50%. • AIR BAGS – they slow you down more slowly and reduce the number of deaths in car crashes by 30%.

17. Taking Risks Reasons why people take risks; • The degree of familiarity – cars are not a risk to us as we use them all the time • Whether you are forced to do something or you choose to • Whether you feel in control of the situation – many people think driving a car is safer than flying because they are in control • Possible rewards – you do something because you enjoy it • Personal experiences – if someone you know had a nasty bungee jumping accident – you probably wouldn’t want to do it yourself • Age/personality types You can estimate the risk of something happening based on how many times it’s happened – its called a “statistical risk assessment. Or you can use a scientific theory to model the situation, then calculate the probability. Generally risk assessors use a combination of the two to get the best possible estimate.

18. Work When a force moves an object, energy is transferred and work is done Whenever something moves, something else is providing some sort of ‘effort’ to move it. This thing needs a supply of energy. It then does ‘work’ by moving the object – and one way or the other it transfers the energy it receives into other forms. EXAMPLE; Some kids drag an old tractor tyre 5m over rough ground. They pull with a total force of 340N. Find the energy transferred ANSWER; W = F x S = 340 x 5 = 1700J W = Work Done measured in Joules (J) F = Force measured in Newton's (N) S = Distance measured in metres (m) Work Done and Energy Transferred are the same thing W F x S

19. Kinetic Energy Anything moving has kinetic energy – its the energy of movement EXAMPLE; A car of mass 2450kg is travelling at 38m/s. Calculate it kinetic energy ANSWER; KE = ½mv² = ½ x 2450 x 38² = 1768900 KE = Kinetic energy measured in Joules (J) ½ = one half M = Mass measured in kg If the Mass is ever written in g convert it to kg – e.g. 140g = 0.14kg V = Velocity measured in m/s K.E. ½ x m x v²

20. Electrical Energy Anything which supplies electricity is also supplying electrical energy. They transfer energy to components in the circuit. EXAMPLE; The motor in an electric toothbrush is attached to a 3V battery. If a current of 0.8A flows through the motor for 3 minutes; what is the energy transformed ANSWER; E = V x I x T = 3 x 0.8 x (3 x 60) = 432J E = Electrical energy measured in Joules (J) V = Voltage measured in Volts (V) I = Current measured in Amps (A) T = Time measured in Seconds (s) Even if something is written in minutes transfer it to seconds E V x I x T

21. Gravitational Potential Energy It is the energy due to height. On Earth, gravity is 10m/s² EXAMPLE; A sheep of mass 47kg slowly raised through 6.3m. Find the gain in potential energy ANSWER; PE = M x G x H = 47 x 10 x 6.3 = 2961J PE = Gravitational Potential Energy measured in Joules (J) M = Mass measured in kg G = Gravity, on earth it is 10m/s² H = Height measured in metres (m) P.E. M x G x H

22. Conservation of Energy ENERGY CONSERVATION; using less fossil fuels because of the damage it does and they might run out. PRINCIPLE OF THE CONSERVATION OF ENERGY; Energy can never be created nor destroyed – only converted from one form to another. Energy is only useful when it’s converted from one form to another. Calculating the Speed of Falling Objects;; Kinetic energy gained = Potential energy lost EXAMPLE; A mouldy tomato of mass 140g is dropped from a height of 1.7m. Calculate its speed as it hits the floor. ANSWER; 1) Find the PE lost; PE = M x G x H = 0.14 x 10 x 1.7 = 2.38J 2) 3) 4) NEEDS TO BE COMPLETED PAGE 49 REV GUIDE

23. Not all energy transferred is useful that's why electrical are rarely 100% efficient! EXAMPLES; • When you boil a kettle some energy is lost as sound and as heat to the room • A light bulb looses some energy as heat to the room

24. Power Power = Rate of doing Work EXAMPLE; A motor transfers 4.8KJ of useful energy in 2 minutes. Find its power output ANSWER; P = W/T = 4800/120 = 40W W = Work Done measured in Joules (J)A P = Power measured in Watts (W) T = Time measured in seconds (s) W P x T

25. Power Output THE TIMED RUN UPSTAIRES; in this case the energy transferred is the potential energy you gain. Hence power = mgh t Power Output – E Transferred/Time = mgh/t = 62kg x 10 x 12m 14s = 531W THE TIMED ACCELERATION; the energy transferred is the kinetic energy you gain. Hence Power = ½mv² t Power Output – Energy Transferred/Time = ½mv² t = ½ x 62kg x 8m/s² = 496W E E = Energy Transferred measured in Joules (J) P = Power measured in Watts (W) T = Time measured in seconds (s) P x T

26. Circular Motion • Velocity is constantly changing • If an object is travelling in a circle it is constantly changing direction, which means it’s accelerating. This means there must be a force acting on it (F = ma). This force acts towards the centre of the circle and is called a centripetal force. CAR GOING ROUND A BEND; the bend is part of a circle, the centripetal force is towards the centre of the circle. The force is from friction between the cars tyres and the road. BUCKET WHIRLING ROUND ON A ROPE; the centripetal force comes from the tension in the rope. Break the rope and the bucket flies off at a tangent. A SATTELITE ORBITING EARTH; the centripetal force keeping the satellite in a circular orbit is the gravitational force between Earth and the satellite.

27. Roller Coasters Max GPE Max Accel Zero G Min KE Min Speed Min Accel Min GPE Min Accel Min GPE Max KE Max Speed

28. To Loop the Loop You Need A Centripetal Force When you loop the loop you feel heavier at the bottom of the loop than you do at the top. During the loop two forces are acting on you; • Your weight always acts towards the ground • A reaction force from you seat which always acts towards the centre of the loop These two forces combine to a resultant centripetal force. The two simplest cases are when you’re at the very top and very bottom of the loop. TOP – both weight and reaction force are acting in the same direction BOTTOM – the two forces are acting in opposite directions

29. Einstein’s Relativity THOUGHT EXPERIMENTS; theory's based on theoretical ideas and have not been tested. Examples are Einstein's theory of relativity. Scientists can be reluctant to accept new theories, especially if they challenge the established way of thinking. Newton's laws of motion predicted that the speed of a ray of light, relative to you, should depend on your velocity – just like the speed of everything else. These laws had stood for over 200 years, so when Einstein came along and questioned them it was a big deal. A radical theory like this is much more likely to be accepted if its the work of more tan one person. Makes sense if you think about it – the theory cant really be dismissed as one person . Makes sense if you think about it – the theory cant really be dismissed as one persons crazy ideas. Before Einstein's theory was published, several other scientist were already working in similar areas. In the 1880’s, two American physicists, Albert Michelson and Edward Morely carried out experiments that suggested that the speed of light was always the same. And Dutch physicist Hendrik Lorentz had already produced work on the effect of motion on space and time. Observations which support a theory can greatly increase its chance of acceptance, e.g. Observations made during a solar eclipse in 1919 supported Einstein's predication that light s bent by gravity

30. A Good Theory Should Make Predication That Can Be Tested • Einstein's theories made very precise predications about the effects of motion on time • These predications couldn’t be tested for many years because our equipment wasn’t accurate enough • However once testing did become possible, his predications worked in many situations. EXAMPLES; ATOMIC CLOCKS; scientists flew atomic clocks in a plane around the world and measured the time taken. The time measured by the moving clocks was very slightly different from that measured by the stationary clocks on the ground. It appeared that time pass more slowly on the moving plane COSMIC RAYS; cosmic rays can produce very short-lived particles called muons. When muons are moving at close to the speed of light, their lifetime increases, i.e. Time moves more slowly for them

31. Ionising Radiation The more ionising the radiation is, the less penetrating it is ALPHA PARTICLES; • They are Helium Nuclei • They are big, heavy and slow moving • They have a strong positive charge. • Their big mass and charge makes them strongly ionising – so they bash into lots of atoms and knock electrons off them, which creates lots of ions, hence the term ionising. • So they don’t penetrate far into materials – but are stopped quickly • They are blocked by paper and skin

32. BETA PARTICLES; • They are Electrons. • They move quite fast and they are quite small. • They have a negative charge. • They are moderately ionising • Penetrate moderately before colliding. • For every Beta Particle emitted a neutron turns into a proton in the nucleus. • They are blocked by thin metals such as aluminium

33. GAMMA RAYS; • Very short wavelength EM Waves. • They tend to pass through rather than collide with atoms, so they are weakly ionising • Penetrate a long way into materials. Eventually they hit something and do damage. • They are similar to X – rays the only difference is where they come from, X – rays comes from firing electrons are a piece of metal and gamma rays come from unstable atomic nuclei when they decay • They are blocked by thick lead or very thick concrete

34. Background Radiation Cosmic Rays come mostly from the Sun. Luckily, the Earths atmosphere protects us from much of this radiation. The Earths magnetic field also deflects cosmic rays away from Earth. Radiation due to human activity, e.g. Fallout from nuclear explosions or dumped nuclear waste. THE LEVEL OF BACKGROUND RADIATION CHANGES DEPENDING ON WHERE YOU ARE; At high altitudes it increases because of more exposure to cosmic rays. That means pilots have an increased risk of getting some types of cancer. Underground in mines it increases because of the rocks all around. Certain underground rocks like granite can cause higher levels at the surface, especially if they release radioactive radon gas – which tends to get trapped in peoples houses.

35. Radon Gas; • The radon concentration in peoples houses varies widely across the UK, depending on what type of rock the house is built on. • Studies have shown that exposure to high does of radon gas can cause lung cancer and the greater the radon concentration the higher the risk. • The scientific community is a bit divided on the effect of lower concentration doses and threes still debate of what the safe(ish) is. • Evidence suggests that the risk of developing lung cancer from radon is high greater for smokers compared to non smokers • Some medical professionals reckon that about 1 in 20 deaths from lung cancer (2000 a year) are caused by radon exposure • New houses in areas where high levels of radon gas might occur must be designed with good ventilation systems. These reduce the concentration of radon in the living space. In existing houses the Government recommends that ventilation systems are put in wherever the radon concentration is higher than a certain level

36. Isotopes & Radiation ISOTOPES; Atoms with the same number of protons by different number of neutrons. Hence they have the same atomic number but different atomic number. Most elements have different isotopes, but only 1 or 2 are stable. The other isotopes tend to be radioactive, which means they decay into other elements and give out radiation. RADIATION; Unstable nuclei will decay and in the process give out radiation. This produce is random – this means if you have 1000 unstable nuclei you can’t say when any one of them is going to decay and neither can you do anything at all to make a decay happen. It’s will decay when it wants to and isn’t affected by physical conditions or chemical bonding. When a nucleus does decay it will spit out one or more of the three types of radiation. You can write these decays as nuclear equations but the mass and atomic numbers much be equal on both sides;

37. Half-Life Half-Life is the time taken for Half of the radioactive atoms now present to decay. Each time a decay happens and an alpha/beta/gamma particle is given out – so one more radioactive nucleus has disappeared. As the unstable nuclei all steadily disappear, the activity as a whole will decreases. So the older a sample becomes, the less radiation it will emit WORKING OUT THE HALF-LIFE; use a step by step method and divide by 2 each time. Example;; Initial Countafter ONE half lifeafter TWO half lives 640 320 160 after THREE half livesafter FOUR half lives 80 40 It has got four half lives.

38. MEASURING THE HALF-LIFE OF A SAMPLE USING A GRAPH;; The half life is found from the graph, by finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis. Background Rate; 20/min Subtract the Background Rate from every reading to give an accurate number

39. Uses of Ionising Radiation SMOKE DETECTORS – USE ALPHA RADIATION; They contain a small amount of americum-241,which gives out alpha particles. The alpha particles ionise the air which is detected by a sensor. Smoke entering the detector blocks the alpha particles. This makes the sensor trigger a loud alarm to alert people to the fire. TRACERS IN MEDICINE – ALWAYS SHORT HALF LIFE EMITTERS; Certain radioactive isotopes can be injected into people and their progress around the body can be followed using an external detector. A computer converts the reading display showing where the strongest reading is coming from. A well-known example is iodine-131, which is absorbed by the thyroid gland just like normal iodine-127, but it gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should. All isotopes which are taken into the body must be GAMMA or BETA emitters, so that the radiation passes out of the body – and they should only last a few hours, so that the radioactivity inside the patient quickly disappears. They should have a short half-life

40. RADIOTHERAPHY – USING GAMMA RAYS; Since high doses of gamma rays will kill all living cells, they can be used to treat cancers. The gamma rays have to be directed carefully and at just the right dosage so as the kill the cancer cells without damaging too many normal cells. However, a fair bit of damage is inevitably done to normal cells, which makes the patient feel very ill. But if the cancer is successfully killed off in the end – its worth it. STERILISATION OF FOOD & SURGICAL INSTRUMENTS – GAMMA RAYS Food can be exposed to a high dose of gamma rays which kill all microbes, keeping the food fresh for longer. Medical instruments can be sterilised in just the same way, rather than by boiling them. The great advantage of irradiation over boiling is that it doesn’t involve high temperatures, so things like fresh apples or plastic instruments can be totally sterilised without damaging them. Te food is not radioactive afterwards – so its perfectly safe to eat. The isotope used for this needs to be a very strong emitter of gamma rays with a long half-life so that it doesn’t need replacing too often

41. Radioactive Dating • The discovery of radioactivity and idea of half-life gave scientists their first opportunity to accurately work out the age of rocks, fossils and archaeological specimens. • By measuring the amount of a radioactive isotope left in the sample and knowing its half life you can work out how long the thing has been around CARBON 14; Carbon-14 makes up about 1/10000000 of the carbon in the air. The level stays fairly constant in the atmosphere. The same of Carbon-14 is also found in living things. However, when they die the C14 is trapped inside the thing and it gradually decays with a half life of 5730 years. So, by measuring the proportion of C14 found in some old axe handle, burial shroud you can calculate how long ago the item was living. THE RESULTS FROM RADIOACTIVE DATING AREN’T PERFECT BECAUSE; • The level of C14 hasn’t always been constant – cosmic radiation, climate change and human activity all effect it. So, scientists are adjusting their calibration tables • Not all living things can act as we expect. E.g. Some plants take up less C14 • Scientists cannot be 100% sure the sample hasn’t been contaminated • Measuring error – the proportion of C14 is unlikely to exact. So its better to use technology as it makes less mistakes

42. Radioactivity Safety RADIATION HARMS LIVING CELLS; • Alpha, beta and gamma radiation enter living cells and collide with molecules • These collisions cause ionisation which damages/destroys the molecules • Lower doses tend to cause minor damage without killing the cell • This can give rise to mutant cells which divide uncontrollably – THIS IS CANCER • Higher doses tend to kill cells completely which cause radiation sickness if a lot of the bodies cells all get killed at once • The extent of harmful effects depends on; how much exposure and the energy and penetration of the radiation OUTSIDE THE BODY – Beta and gamma radiation are more dangerous here as they can get inside organs where as alpha can’t penetrate the skin INSIDE THE BODY – alpha sources do all their damage in a very localised areas there are more damaging here as they cant escape where as beta and gamma rays pass straight out.

43. IN THE SCHOOL LABORATORY;; • Never allow skin to contact with a source. Always handle with tongs. • Hold the source at arm’s length to keep it as far from the body as possible • Keep the source pointed away from the body and avoid looking straight at it • Always store the source in a lead box and put it back as soon as the experiment is over

44. When Marie Curie discovered the radioactive properties of radium in 1898, nobody new anything about its dangers. People were fascinated by radium – it was used in medicines and to make luminous paint. You could buy everyday products made using this pain e.g. Glow in the dark watches. However by the 1930’s people were starting to link health problems to radiation – many wat dial painters developed cancer as a result of exposure to radium. More recently, we’ve learnt a lot about the dangers of radiation.

45. Splitting the Atom Einstein predicted E=mc². His predictions were confirmed over 30 years late by the development of nuclear fission; THE CHAIN REACTION; • A slow moving neutron is fired at the uranium-235 atom. The neutron is absorbed by the nucleus – this makes the atom unstable and causes it to spilt, • When the U-235 atom splits it forms two new lighter elements (daughter nuclei). There are lots of different pairs of atoms that uranium can spilt into, e.g. Krypton-91 and barium-143, but all these new nuclei are radioactive because they have the ‘wrong’ number of neutrons • Each time a uranium atom splits up it also spits out 2 or 3 neutrons, which can hit other uranium nuclei, causing them to split also and so on and son on. This is a chain reaction. • Each nucleus splitting (called a fission) gives out a lot of energy. Going back to Einstein's theory, this energy comes from the fact that the fission products have slightly less mass than the original nucleus – the ‘lost’ mass is converted to energy. Each fission gives out a lot more energy than you release much more energy than you get with a chemical bong between two atoms. Nuclear processes release much more energy than chemical processes do. That's why nuclear bombs are much better than bombs which rely on chemical reactions

46. Nuclear Fission can happen with uranium and plutonium atoms THE PRODUCTS OF NUCLEAR FISSION ARE RADIOACTIVE; The daughter nuclei produced by nuclear fission have too many neutrons to be stable. To become more stable they turn a neutron into a proton – giving off a beta particle at the same time. This process continues, creating a decay series until you get a stable nucleus. Decay series are drawn with arrows between each isotope in the series and show what particle each isotope emits when it decays

47. Nuclear Power Stations Nuclear power stations are powered by nuclear reactors. In a nuclear reactor, a controlled chain reaction takes place in which uranium atoms split up. The fission of an atom of uranium releases loads of energy in the form of thermal energy (heat). This heat is used to boil water to drive a steam turbine Inside a Gas-Cooled Nuclear Reactor Neutrons are injected into the reactor to ‘kick-start’ the fission process The daughter products then collide with other atoms, causing the temperature in the reactor to rise Control rods often made of born limit the rate of fission by absorbing excess neutrons A gas, typically CO₂ is pumped through the reactor to carry way the heat generated The gas is then passed through a heat exchanger, where it gives it energy to water – this water is heated and turned into steam, which turns a turbine generating electricity

48. Pros and Cons of using Nuclear Power;; • Fossil fuels (coal, oil, gas) all release CO₂. This adds to the greenhouse effect and global warming. Burning coal and oil also releases sulphur that can cause acid rain. In terms of emissions like this nuclear power is very clean • The main environmental problem is with the disposal of waste. The products left over after nuclear fission are generally radioactive – so they can’t just be thrown way. • It carries the risk off leaks from the plant or major catastrophes like Chernobyl • Building a nuclear plant bring skilled jobs to the area and support industries around it. • Nuclear fuel like uranium is cheap but the overall cost of nuclear power is high due to the cost of the power plant and final decommissioning. Dismantling a nuclear plant safely takes decades

49. Nuclear Fusion • Its the opposite of nuclear fission • In nuclear fusion, the light nuclei like hydrogen combine to create larger nucleus • Fusion releases a lot of energy (more than fission for a given mass) all the energy released is stars comes from fusion. So people are trying to develop fusion reactors to make electricity • Fusion doesn’t leave behind a lot of radioactive waste and threes plenty of hydrogen to use as fuel • The big problem is that fusion only happens at really high densities and temperatures (about 10000000°C) • No material can withstand that kind of temperature – it would just be vaporised – so fusion reactors are really hard to build. You have to contain the hot hydrogen in a magnetic field instead of a physical container • There are a few experimental reactors around at the moment, the biggest one being JET (Joint European Torus) but none of them are generating electricity yet. It takes more power to get up to temperature than the reactor can produce

50. Cold Fusion A new scientific theory has to go through a validation process before its accepted. This means making the research results public – usually in a scientific journal such as Nature, so that other scientists can repeat the experiments. If lots of scientists get the same results, the theory is likely to be accepted. Cold Fusion hasn’t been accepted; • Cold fusion is nuclear fusion which occur at around room temperature – rather than at millions of degrees Celsius • In 1989, 2 scientists – Stanley Pons & Martin Fleischmann reported to a press conference that they had succeeded in releasing energy from cold fusion using a simple experiment. This caused a lot of excitement – cold fusion would make it possible to generate lot of electricity, easily and cheaply. However many scientists were sceptical believing that fusions is only possible at very high temperatures. • After the press conference, other scientists tried to repeat the experiment. But few managed to reproduce the results reliable. When a group at MIT (Massachusetts Institute of Technology) discredited the theory the feeling against cold fusion was so strong that scientific journals fused to publish papers on it • Despite all the setbacks, there is still funding available for cold fusion research and Pons and Fleischmann's results have actually been repeated many times now – although not reliably enough to the theory to be accepted