P3 Topic 3,4 & 5

P3 Topic 3,4 & 5

1. Topic 3

   • Particles in Atoms
     • The properties of Alpha, Beta and Gamma Radiation
       • What is it?
         • A helium nucleus
         • An electron
         • Electromagnetic radiation
       • Alpha
       • Beta
       • Gamma
       • Is it fast or slow, heavy or light
         • Slow and heavy
         • Light and fast
         • No mass, very fast
       • Is it ionising
         • Strongly Ionising
         • Moderately Ionising
         • Weakly Ionising
       • How penetrating is it and what stops it?
         • Stopped by paper, skin, etc.
         • Stopped by thin metal
         • Stopped by thick lead or very thick concrete
     • Positron radiation is positively charged beta radiation
       • 1) The positron is the antiparticles of the electron. This means they're just like electrons- they've got exactly the same relative mass, but their relative change is +1 (they're positively charged).
       • 2) Positrons have the same properties as electrons- they're light and fast moving, moderately ionising and are stopped by a sheet of thin metal.
       • 3) But positrons are obliterated in spectacular fashion as soon as they meet an electron- this is called annihilation.
     • Neutron radiation
       • 1) Neutron are more penetrating than alpha or beta and sometimes even more penetrating than gamma.
       • 2) Unlike alpha, beta and gamma, neutrons aren't directly ionising, but they can be absorbed by the nuclei of atoms in the substances they pass through.
       • 3) Absorbing a neutron can make a nucleus radioactive.
       • 4) These radioactive nuclei then emit ionising radiation (alpha, beta or gamma), so neutrons are sometimes called 'indirectly ionising'.
       • 5) Neutrons are absorbed best by light nuclei. Hydrogen nuclei are the lightest of all, so hydrogen-rich materials such as water, polythene or concrete are used to make neutrons radiation shielding.
       • 6) Neutrons absorption often makes nuclei emit gamma radiation, some nice thick lead can be added to neutrons radiation shielding, to shield against gamma radiation as well.
   • Stability and radioactive decay
     • Some Nuclei are more stable than others
       • A nucleus will be unstable if it has:
         • 1) too many neutrons
         • 2) too few neutrons
         • 3) too many protons and neutrons altogether, i.e. it's to heavy
         • 4) too much energy
       • Plot the number of neutrons (N) against the number of protons (Z) for stable isotopes and you get this nice curve of stablility
         • 1) Any isotopes which doesn't lie on the curve is unstable. Unstable means radioactive- particles or radiation is emiiteed
         • 2) An isotopes that lies above the curve has too many neutrons to be stabe
         • 3) An isotope that lies below the curve has too few neutrons to be stable.
     • Beta Decay
       • B+ decay happens when there are too many neutrons
         • 1) Beta- minus (usually just called beta) decay is the emission of an electron from the nucleus.
         • 2) Beta decay happens in isotopes that are "neutron rich" (i.e. have many more neutrons than protons in their nucleus). When a nucleus ejects a beta particle, one of the neutrons in the nucleus is changed into a proton.
         • The proton (atomic) number increase by one, and the nucleon (mass) number stays the same.
       • B- decay happens when there are too few neutrons
         • 1) Beta-plus decay is the emission of a positron from the nucleus.
         • 2) In beta-plus emission, a proton gets charged into a neutron.
         • The proton number decreases by one, and the nucleon number stays the same.
     • Alpha decay happens in heavy nuclei
       • 1) Alpha emission only happens in very heavy atoms, e.g. ones with nuclei that have high z values (with more than 82 protons), like uranium and radium.
       • 2) The nuclei of these atoms are too massive to be stable.
       • The proton number decreases by two, and the nucleon number decreases by four.
     • Gamma radiation is emitted from Nuclei with too much energy
       • 1) After alpha or beta decay, the nucleus often has excess energy. It loses this energy by emitting a gamma ray.
       • 2) Gamma emission always goes with beta or alpha decay. You never get just gamma rays emitted.
       • 3) When a gamma ray is emitted, there is no chance in the proton number or nucleon number of the nuclei.
   • Quarks
     • 1) Protons and neutrons are made up of even smaller particles called quarks.
     • 2) There are various kinds of quarks, but protons and neutrons consist of just two types- up-quarks and down-quarks.
     • 3) The relative charge on up and down quarks are shown in the table. When quarks combine to make protons and neutrons, these charges add together to make the overall relative charges.
     • Quarks
       • Up
       • Down
     • Relative charge
       • 2/3
       • -1/3
     • Relative mass
       • 1/3
       • 1/3
     • Proton
       • Up-quark+ Up quark+ Down quark= Proton
       • Charge on Proton= 2/3+2/3+(-1/3)=+1
       • Mass of proton= 1/3+1/3+1/3=1
     • Neutron
       • Up-quark+ Down quark+ Down quark= Neutron
       • Charge of Neutron= 2/3+(-1/3)+(-1/3)=0
       • Mass of Neutrons= 1/3+1/3+1/3=1
     • Quarks change- produce electrons/positrons in the process
       • 1) Sometimes the number of protons and neutrons in a nucleus can make the nucleus unstable. To become more stable, a neutron is converted into a proton, or a proton into a neutron.
       • 2) This happens by changing a down-quark into a up-quark, or vice versa.
       • 3) However, the overall charge before and after has to be equal.
       • 4) So when a neutron turns into a proton, the nucleus has to produce negatively charged particle as well to keep the overall charge zero. The particles produced is an electron. This is B- decay
       • 5) When a proton charge into charges into a neutron (up-quark charges into down quark), a positive charge is needed to keep the overall charge at +1. The nucleus produces and chucks out a positron. This beta decay.
   • Medical uses of radiation
     • Tracers in medicine- always short half-life beta or gamma emitters
       • Some radioactive isotopes are used as tracers to diagnose some medical conditions.
       • 1) The tracer is injected into the patient or swallowed. An external detector follows its progress as it moves around the body. A computer uses these reading to create an image which shows where where the strongest reading of radiation is coming from.
       • 2) A well-know example is the use of iodine-131, which is absorbed by the thyroid gland. It gives out radiation which can be detected to indicate whether the thyroid gland is taking iodine as it should.
       • 3) Only isotopes which emit beta or gamma are used as they can pass out of the body. They also have short half-lives to reduce the amount of radioactivity inside the patient.
     • PET Scanners
       • Positron emission tomography or PET scanning is a technique used to show tissue or organ function, and can be used to diagnose medical conditions. For example:
         • 1) PET scans show areas of damaged tissue in the heart by detected areas of decreased blood flow. This can reveal coronary artery disease and damaged or dead heart muscle caused by heart attacks. They can also record blood flow and activity in the brain. This helps diagnose illnesses like epilepsy.
         • 2) PET scans can identify active cancer tumours by showing metabolic activity in tissue. Cancer cells have a much higher metabolism than healthy cells because they're growing very fast.
       • 1) Inject the patient with a substance used by the body, e.g. glucose, containing a positron-emitting radioactive isotope with a short half-life so it acts as a tracer. Over an hour or so the tracer moves through the body to the organs.
       • 2) Positrons meet electrons and annihilate emitting high-energy gamma rays which are detected. The distribution of radioactivity matches up with metabolic activity. This is because more of the radioactive glucose (or whatever) injected into the patient is taken up and used by cells that are doing more work (cells with an increased metabolism, in other words).
       • How it works
       • 3) The isotopes used in PET scanning have short half-lives, so it's important that they're made close to where they'll be used. Some hospitals have their own cyclotron to make the isotopes on-site. Otherwise, if the isotopes had to be transported over a large distance, their activity could be too low by the time they arrived at the hospital, making them no longer as useful.
     • Radiation can cause tissue damage and possible mutations
       • 1) Ionising caused by radiation can kill a cell completely or damage it so it can't divide- causing tissue damage. Radiation can alter the genetic material in a cell. This can cause mutations. It can also make the cell divide and grow uncontrollably- this is cancer. This is why it's important to limit people's exposure to radiation.
       • 2) Things like PET scans only use pretty small doses of radiation, e.g. 7 millisieverts (mSv) per PET scan, compared to 2.2 mSv per year background radiation from just living in the UK. BUT...ANY exposure to radiation increases the risk of tissue damage and cancer- so it's recommended not to scan patients too often and only if it's necessary. It's all a case of balancing risk.
       • 3) For treatments and diagnostics methods, patients should be given the lowest possible doses of radiation and have a short exposure time. They might also wear lead shielding to protect areas not being treated.
       • 4) Medical personnel must also limit their exposure to radiation. The intensity of radiation decrease with distance, so staff stand well away from sources or remotely control equipment, e.g. from another room. Intensity also depends on the material it has to travel through, so workers may stand behind lead screens or wear protective lead-lined clothing. Their radiation dose must be closely monitored.
     • Radiation can be used Internally or externally to treat tumours
       • 1) With internal radiation therapy, a radioactive material is placed inside the body into or near a tumour. This can be done in many ways, e.g. by injecting or implanting a small amount of radioactive substance. This method gives a high dose of radiation to a small part of the body, so damage to normal tissue surrounding the tumour is limited.
       • 2) Tumour can be treated externally using high-energy X-rays or gamma rays aimed at the tumour. The radiation is carefully focused at the tumour, but some damage is still done to surrounding healthy cells.
       • 3) The whole treatment using internal sources is usually shorter than using external source of radiation- sometimes by up to 6 weeks. This reduces the number of visits a patients has to make to hospital as well as the time they have to wait to undergo any further planning treatment, e.g. chemotherapy.
       • 4) Internal treatment may cause the patient to emit radiation after a source is inserted- so they may have to limit contact with people until it's removed, which in some cases could be several days later. With external sources, each session of the treatment only lasts a few minutes and the patient doesn't emit any radiation afterwards.
       • 5) Internal treatment generally have no side effects, although they may be some discomfort from the implant. However, external treatments like radiotherapy can have some short short and long term effects.
       • 6) Some uses of internal and external radiation therapy overlap, but they're often used to treat different parts of the body
     • Using Radiation in Medical physics Raises social and ethical issues
       • Radiation is both useful and dangerous- we have to think whether the benefits of using it to diagnose or treat an illness, outweigh the associated risks to the patients involved.
       • 1) Even when precautions are taken, using radiation to kill off cancerous cells will also cause some damage to normal cells- this can lead to side effects. For example, radiotherapy can cause hair loss, sickness and skin irritation. These fairly minor side effect generally only last as long as the treatment
       • 2) But there are other more serious side effects that may appear months or years after a radiotherapy treatment has ended that could significantly affect someone's life, e.g. bowel damage or infertility.
       • 3) Some people may argue that if someone's quality of life could be seriously reduced after treatment, then it may not be worth undergoing it in the first place. Some people may refuse treatment because of the risk of getting these side effects.
       • 4) In some rare causes, the patients may even develop a second cancer caused by the radiation used to treat their first cancer. But, without the first treatment the person's life expectancy may be dramatically shorter.
       • 5) Radiotherapy doesn't always lead to cure, but it can often reduce the suffering of a patient who is close to death. Treatment that reduces suffering without curing an illness is called palliative care.
     • Developing Medical techniques can be controversial process
       • 1) Some radioactive medical techniques are relatively new in the medical world. That means we don't yet fully understand the long-term benefits and side effects
       • 2) New techniques are often tested first on cells grown in a lab, then on animals. Once they've been tested on animals and come out OK, they need to be tested on people. There are ethical arguments that go with this:
         • A new technique could have harmful side effects. Patients should be aware of possible side effects before agreeing to take part in medical tests. But doctors don't know for sure what all the side effects could be.
         • Lots of ill patients might want to get onto a medical trail. But places are limited.
         • When a trial seems to show a new technique works, how long should it be before it's offered to everyone?

2. Topic 4

   • Cyclotrons
     • Circular Motion- Velocity is Constantly Changing
       • 1) Velocity is both the speed and direction of an object
       • 2) If an object is travelling in a circle it is constantly changing direction, which means it's accelerating
       • 3) This means there must be a resultant force acting on it
       • 4) This force acts towards the centre of the circle
       • 5) This force that keeps something moving in a circle is called a centripetal force.
     • Charged Particles are affected by a magnetic field
       • 1) A charged particles in a magnetic field will experience a force. The force on a moving charge in a magnetic force. The force on a moving charge in a magnetic field is always perpendicular to its direction of travel- making the particle follow a curved track.
       • 2) The direction of the force on a particles depends on its charge. The paths of positive and negative particles curve in opposite directions.
       • 3) Usually you don't see neat circular patterns. Instead the particles move in spirals- this is because the particles lose energy and slow down as they interact with other particles
       • 4) The less energy the particles have, the more curved their path will be.
       • 5) The magnetic field makes the particles spiral outwards as their energy increases
     • A cyclotron is a circular particle accelerator
       • A cyclotron is a particle accelerator which accelerator which uses a magnetic field to accelerate particles to very high energies circular paths
       • 1) The charged particles (e.g. protons) start at the centre of a cyclotron.
       • 2) The cyclotron uses two hollow semicircular electrodes to accelerate the particles across a gap.
       • 4) A magnetic field is used to keep the particles spiral outwards as their energy increases.
       • 3) An alternating potential difference is applied between the electrodes- as the particles are attracted from one side to the other their energy increases (i.e. they are accelerated).
       • 5) The magnetic field makes the particles spiral outwards as their energy increases.
   • Uses of Particles Accelerators
     • Proton Enrichment forms Isotopes that emit positrons
       • 1) Some radioactive isotopes are produced by bombarding stable elements with protons.
       • 2) A proton is absorbed by the nucleus. This increases its proton number, so you get a new element.
       • 3) A proton needs a lot of energy to be absorbed into the nucleus, so this process takes place in a cyclotron (a circular particle accelerator).
       • 4) The radioisotopes made by proton enrichment are usually positrons emitters. Remember, a positron is the antiparticle of an electron- same mass, opposite charge.
       • 5) Positron emitters are useful in hospitals- they're used in PET scanning. A PET scanner is a device used to monitor blood flow and metabolism.
       • Examples:
         • Here are very useful radioisotopes made by proton bombardment, along with equations showing how they're formed. These are all positron emitters, and are all used in PET scanning.
         • 1) Fluorine-18 is made using an isotope of oxygen called oxygen-18. Fluorine-18 has a half-life of just under 2 hours
           • O+p---->F+n
         • 2) Carbon-11 is made using nitrogen-14. Carbon-11 has a half-life of about 20 minutes.
           • N+p----> C+He
         • 3) Nitrogen-13 is made using oxygen-16. Nitrogen-13 has a half-life of about 10 minutes
           • O+p----> N+He
     • Particle Accelerators help Scientist find out about the Universe
       • Particles accelerators aren't just used for medical purposes- they're also used by Scientists to help them find out more about the Universe and what it's made up of.
       • 1) Scientists uses huge particle accelerators to smash particles into each other at tremendous speeds, to see what happens- what kind of radiation is given off, what new particles are created, etc. This give clues about how the universe works, so scientists can develop better explanations about the physical world.
       • 2) Research into big scientific questions like particle physics is done internationally. Particle accelerators are so expensive that not every country can afford its own. Also, it's useful to combine the expertise of lots of specialists- most are looking for the same sort of stuff. Sharing ideas.
       • 3) However, there are sometimes rival groups and projects that are looking for the same thing- they each want to be the first one to make a discovery.
       • 4) One example of collaborative working is the Large Hadron Collider at Geneva. This accelerator was built by the European Organization for Nuclear Research (known as CERN). This particle accelerators is the largest and most powerful ever built. The scientists at CERN are using it to try and re-create the conditions just after the Big Bang- by colliding two beams of protons head-on at mega fast speeds.
   • Momentum and Kinetic Energy
     • Momentum is always conserved
       • Remember that the momentum of an object is working out using: Momentum= Mass*Velocity
       • 1) In any collisions or explosion, momentum is conserved (so long as there aren't any external forces acting). This means that the TOTAL MOMENTUM AFTER is EQUAL TO the TOTAL MOMENTUM BEFORE.
       • 2) The three situations that conservation of momentum might crop up in are:
         • Collision: Bouncing Off
           • This is similar to when a fast-moving neutron hits a nucleus and bounces off again.
         • Collision: Joining Together
           • This example is similar to when a neutron or proton collides with an atom and is absorbed into the nucleus.
         • Explosion: Shot and Recoil
           • This is like a particle being emitted from a nucleus. The nucleus recoils like a fired gun
     • Collisions can be Elastic or Inelastic
       • An elastic collision is one where momentum is conserved and kinetic energy is conserved- i.e. no energy is dissipated (lost) as heat, sound, etc. If a collision is inelastic it means that some of the kinetic energy is converted into other form during the collision. But momentum is always conserved.
       • Example: A toy lorry (mass 2kg) travelling at 3 ms(-1) crashes into a smaller toy car (mass 800 g), travelling in the same direction at 2ms(-1). The velocity of the lorry after the collision is 2.6 ms(-1) in the same direction. Calculate the new velocity of the car and the total kinetic energy before and after the collision.
         • Kinetic Energy before= KE of lorry+KE of car
           • =1/2mv(2)(lorry) +1/2mv(2)(car)
           • =1/2(2*3(2))+1/2(0.8*2(2))
           • =9+1.6=10.6J
         • Kinetic Energy after=1/2 (2*2.6(2))+1/2(0.8*3(2))
           • =6.76+3.6=10.36J
         • Momentum before collision= Momentum after collision
           • (2*3)+(0.8*2)=(2*2.6)+(0.8v)
           • 2.4=0.8v
           • v= 3m/s(-1)
     • A bouncing ball is an example of an Inelastic collision
       • 1) Drop a ball and it'll bounce. But it won't bounce as high as the height you dropped it from. Remember, when an object falls it gravitational potential energy. When the ball hits the ground it loses kinetic energy, e.g. as heat/sound- it is an inelastic collision.
       • 2) So obviously if the ball loses K.E. then it'll have less G.P.E too and so won't reach the same height.
       • 3) You can investigate the factors that affect the rebound height of a ball, by changing one of the follow (but keeping the rest the same): the ball material, the surface it's dropped on, the initial height of the drop, etc.
   • Annihilation and PET scans
     • Momentum is conserved in Positron/Electron Annihilation
       • 1) When a particle meets its antiparticle (its opposite), the result is annihilation. All the mass of both particles is converted into energy, which is given off in the form of gamma rays.
       • 2) When positrons and electrons meet, they tend to collide head on at the same speed and moving in opposite directions.
       • 3) The particles have the same mass and opposite velocities, so the total momentum before the collision is zero.
       • 4) Momentum is always conserved, so the gamma rays produced need to have a total momentum of zero.
     • 5) The way that usually happens is that two gamma rays are produced which have the same energy but exactly opposite velocities.
     • 6) In any particle reaction, the total charge after the reaction must equal the total charge before the reaction.
     • 7) The total charge before the electron- positron collision is zero- since the charge of an electron is -1, and the total charge on a positron is +1. Gamma rays have no charge so the charge after the collision is also zero-charge is conserved.
     • Mass Energy is also conserved in positron/electron annihilation
       • 1) Einstein said that mass is a form of energy- mass can be converted into other form of energy and vice verse. So, you can think of them as being essentially the same thing- mass energy.
       • 2) Mass energy is conserved in annihilation reactions- all the mass of the electron and positrons have been converted into energy. It's Einstein's famous equation at work:
       • (Energy in Joules, J) E=M(Mass in kilograms,kg)*C(2) (Speed of light (=3*10(8)m/s)
       • EXAMPLE: Calculate the minimum energy released when an electron and positron annihilate. The mass of an electron or positron is 9.1* 10(-31)kg.
       • ANSWER: The total mass= 2*9.1*10(-31)=1.82*10(-30)kg E=1.82*10(-30)*(3*10(8)(2)=1.638*10(-13)J
     • PET scanning involves Positron/Electron Annihilation
       • A positron-emitting radio isotopes is injected into a patient. The emitted positrons collide with electrons in the organs, causing them to annihilate and emit high-energy gamma rays. There will be a higher take-up of the radio isotopes in tumour cells than in normal cells
       • Detectors around the body detect each pair of gamma rays- the tumour will lie along the same path as each pair, the location of the tumour can be accurately found by triangulation.

3. Topic 5

   • Kinetic Theory and Absolute Zero
     • Kinetic theory can be explain the three states of matter
       • The three states of matter are solid (e.g. ice), liquid (e.g.water) and gas (e.g. water vapour). The particles of an particular substance in each state are the same-only the arrangement and energy of the particles are different.
         • SOLIDS- strong forces of attraction hold the particles close together in a fixed, regular arrangement. The particles don't have much energy so they can only vibrate about their fixed positions.
       • LIQUIDS- there are weaker forces of attraction between the particles. The particles are close together, but can move past each other, and form in random directions at low speeds.
       • GASES- There are almost no forces of attraction between the particles. The particles have more energy than those in liquid and solids- they are free to move, and travel in random directions and at high speeds.
     • Gases are randomly moving particles
       • 1) Kinetic theory says that gases consist of very small particles. Which they do- oxygen consists of oxygen molecules, neon consists of neon atoms, etc.
       • 2) These particles are constantly moving and colliding with each other and with the walls of their container, a bit like moshers in a mosh pit. When collide, they bounce off each other, or off the walls.
       • 3) The particles hardly take up any space. Most of the gas is empty space.
     • Absolute Zero is as cold as stuff can get- 0 kelvin
       • 1) If you increase the temperature of something, you give its particles more energy- they move about more quickly or vibrate more. In the same way, if you cool a substance down, you're reduced the kinetic energy of the particles.
       • 2) In theory, the coldest that anything can ever get is -273 degrees celsius- this temperature is known as absolute zero. At absolute zero, the particles have as little kinetic energy as it's possible to get- they're pretty much still.
       • 3) Absolute zero is the start of the Kelvin scale of temperature.
       • 4) A temperature change of 1 degrees celsius is also a change of 1 kelvin. The two are pretty similar- the only difference is where the zero occurs.
       • 5) To covert from degrees Celsius to kelvin, just add 273. To convert from kelvin to Celsius, just subtract 273
       • Absolute Zero
       • Freezing point of water
       • Boiling point of water
       • Kelvin scale
         • 0 K
         • 273 K
         • 373 K
       • Celsius scale
         • -273 degrees Celsius
         • 0 degrees Celsius
         • 100 degrees Celcius
   • Pressure, Volume and temperature of gases
     • Kinetic Energy is proportional to temperature
       • The heading makes this sound more complicated than it actually is...
         • 1) If you increase the temperature of a gas, you give its particles more energy.
         • 2) In fact, if you double the temperature (measured in kelvins), you double the average kinetic energy of the partices.
         • The Kelvin temperature of a gas is directly proportional to the average kinetic energy of its particles.
       • 3) As you heat up a gas, the average speed of its particles increases. Anything that's moving (e.g. a bunch of particles) has kinetic energy is 1/2mv(2), remember.
     • Kinetic Theory says colliding gas particles creates pressure
       • 1) As gas particles move about, they bang into each other and whatever else happens to get in the way.
       • 2) Gases particles are very light, but they are not massless. When they collide with something, they exert a force on it. In a sealed container, gas particles smash against the container's wall- creating outward pressre
       • 3) This pressure depends on how fast the particles are going and how often they hit the walls.
     • A Constant pressure "V/T= Constant"
       • 1) When a gas is at a constant pressure, its volume is proportional to its temperature.
       • 2) What this actually means is that if you have a gas and heat it up you give the particles more kinetic energy and they whizz around faster- the gas expands to take up more room, and so the volume increases.
       • 3) When the pressure is constant, the volume of a gas before a temperature change is related to its volume afterwards by this equation:
         • Volume(1)= Volume(2)*temperature(1)(in K)/temperature(2)(in K)
       • At a constant pressure:
       • V(1) and T(1) are your starting conditions and V(2) and T(2) are your final conditions.
       • EXAMPLE: A gas is heated from a temperature of 290K to 315K. Assuming the gas is at a constant pressure, find the initial volume is 95 cm(3).
       • ANSWER: v(1)=(V(2)*T(1)/T(2), V(2)=95cm(3), T(1)=290 K, T(2)=315 K Plug the number into the equation: V(1)=(95*290/315=87.5cm(3) (to 1.d.p.)
     • At constant temperature, "Pressure*Volume=Constant"
       • 1) In a system where the temperature is constant, reducing the volume of a gas means the particles get more squashed up and hit the walls of the container more often, and the pressure increases.
       • 2) Likewise, if you put the same amount of gas in a bigger container, the pressure will decrease, 'cos there'll be fewer collisions between the gas particles and the container's walls.
       • 3) Pressure and volume are inversely proportional- when volume goes up, pressure goes down (and vice versa).
       • 4) For a gas of fixed mass at a constant temperature, the relationship between volume and pressure is this. Here V(1) and P(1) are the initial volume and pressure, and V(2) and P(2) are the final volume and pressure.
         • V(1)*P(1)=V(2)*P(2)
       • EXAMPLE: An helium balloon has a volume of 7000 cm(3) and is at a pressure of 101 325 Pa. What is the pressure if the balloon is squished to a volume of 6000cm(3)?
         • ANSWER: P(2)= (V(1)*P(1)/V(2) P(2)=(7000*101 325)/6000=118 213 Pa
     • You can investigate ideal gases using a gas syringe
       • You may well meet a gas syringe in your lab experiments- it's just a special type of syringe designed specifically for collecting and measuring gases. You can use this jazzy piece of kit to investigate ideal gas laws
       • Volume and temperature at a constant pressure:
         • 1) Half fill a gas syringe with air and seal it with a rubber bung
         • 2) Use a Bunsen burner to heat the air in the gas syringe.
         • 3) As it heats up, the gas will expand, pushing the plunger outwards- the volume of the gas will increase as the temperature increases.
         • 4) Since the syringe plunger is free to move, the pressure of the gas stays the same.
         • 5) If you cool it down again, the gas will contract, pulling the plunger in with it.
       • Pressure and Volume at a Constant Temperature:
         • 1) Attach a gas syringe, half filled with air, to pressure sensor.
         • 2) If you push the plunger in, you compress the gas and reduce the volume
         • 3) This increases the gas pressure (because more collisions happen between the particles and the wall).
         • 4) If you pull the plunger out, you increase the volume of the gas and decrease the pressure.
   • Gas Pressure and Medicine
     • (P*V)/T=Constant
       • Sometimes the pressure and temperature of a gas won't be constant- that's science for you. Luckily, it's all still pretty straight forward- you just have to use this lovely equation:
         • Pressure*Volume/temperature(in K)= Constant
           • P*V/T= Constant
             • P(1)V(1)/T(1)=P(2)V(2)/T(2)
     • Gases used in Medicine are kept under pressure
       • 1) Many gases are used in medicine, for example, oxygen and nitrogen are needed during operations to help patients breathe. These gases are stored under pressure in metal canisters or bottles.
       • 2) Flow rate is the volume of gas per unit time (seconds, minutes, hours, etc.) released from a gas bottle. Gas Canisters are usually fitted with a valve so that the flow rate can be adjusted and controlled.
       • 3) The pressure outside a gas bottle will typically be 1 atmosphere (1 atm). Stored gas are kept at a high pressure also means that a lot of gas can be kept in a small volume.
       • 4) The difference in pressure between the inside and the outside of a gas bottle is what causes gas to flow- when the pressure are equal, the gas has no reason to go anywhere. So, a cylinder of gas won't empty completely- once the pressures on the inside and outside are equal, the flow rate will go to zero. This means a volume of gas equal to the volume of the canister will remain inside that canister.
       • 5) Gas canisters need to be made of materials that are strong enough to hold gases under high pressures withput buckling or spitting- e.g. steel or carbon reinforced aluminium. The size, materials and pressures used in gas canisters depend on where and what they're used for, e.g. on an ambulance where space is limited, small canisters store gases at very high pressure (to maximise the amount of gas they hold).
       • EXAMPLE: A 1500 cm(3) bottle of oxygen is stored at a pressure of 3.8 atm. The pressure outside the bottle is 1 atm. What volume of oxygen is released into the atmosphere if the bottle is opened? Assume that the temperature is constant.
         • ANSWER: V(1)=1500cm(3), P(1)=3.8atm, P(2)=1atm The temperature is constant ,so (P(1)*V(1))=(P(2)*V(2)) Rearranging gives V(2)=(P(1)*V(1)/P(2)=(3.8*1500)/1=5700cm(3) !500 cm(3) will remain inside the bottle (as the pressure difference will be zero). V(released)=5700-1500=4200 cm(3)