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13/04/2015 AQA 2011 Physics Unit 2 W Richards This PowerPoint supports sections P2.5 and P2.6 of the 2011 AQA Physics Unit 2 module.

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Presentation on theme: "13/04/2015 AQA 2011 Physics Unit 2 W Richards This PowerPoint supports sections P2.5 and P2.6 of the 2011 AQA Physics Unit 2 module."— Presentation transcript:


2 13/04/2015 AQA 2011 Physics Unit 2 W Richards This PowerPoint supports sections P2.5 and P2.6 of the 2011 AQA Physics Unit 2 module

3 13/04/2015 P2.5.1 – Atomic Structure

4 13/04/2015 The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”) The nucleus is around 10,000 times smaller then the atom! Atoms always have the same number of protons and electrons so they are neutral overall. They can gain or lose electrons to form ions.

5 13/04/2015 Structure of the atom A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it… I did an experiment (with my colleagues Geiger and Marsden) that proved this idea was wrong. I called it the “Scattering Experiment” Ernest Rutherford, British scientist:

6 13/04/2015 The Rutherford Scattering Experiment Alpha particles (positive charge, part of helium atom) Thin gold foil Most particles passed through, 1/8000 were deflected by more than 90 0 Conclusion – atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.

7 13/04/2015 The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron1/2000 (i.e. 0) MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously)

8 13/04/2015 Mass and atomic number revision How many protons, neutrons and electrons?

9 13/04/2015 Isotopes An isotope is an atom with a different number of neutrons: Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. Notice that the mass number is different. How many neutrons does each isotope have? A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.

10 13/04/2015 P2.5.2 – Atoms and Radiation

11 13/04/2015 Introduction to Radioactivity Some substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation at random intervals: Radiation The nucleus is more stable after emitting some radiation – this is called “radioactive decay”. This process is NOT affected by temperature or other physical conditions.

12 13/04/2015 Ionisation Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons: Alpha radiation is the most ionising (basically, because it’s the biggest). Ionisation causes cells in living tissue to mutate, usually causing cancer.

13 13/04/2015 Background Radiation Radon gas Food Cosmic rays Gamma rays Medical Nuclear power 13% are man-made

14 13/04/2015 Background Radiation by Location In 1986 an explosion occurred at the Chernobyl nuclear power plant. Here is a “radiation map” showing the background radiation immediately after the event: Other “risky” areas could be mining underground, being in a plane, working in an x-ray department etc

15 13/04/2015 Types of radiation 1) Alpha (  ) – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom) 2) Beta (  ) – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle. 3) Gamma – after  or  decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed. Unstable nucleus New nucleus Alpha particle Beta particle Gamma radiation Words – frequency, proton, energy, neutrons, helium, beta

16 13/04/2015 Changes in Mass and Proton Number Alpha decay: Am Np α Sr Y β + Beta decay:

17 13/04/2015 Blocking Radiation Each type of radiation can be blocked by different materials:    Sheet of paper (or 6cm of air will do) Few mm of aluminium Few cm of lead

18 13/04/2015 Summary PropertyAlphaBetaGamma Charge Mass Penetration ability Range in air What is it? Ionising ability

19 13/04/2015 Deflection by Electric Fields Alpha and beta particles have a charge: protons, 2 neutrons, therefore charge = +2 1 electron, therefore charge = -1 Because of this charge, they will be deflected by electric fields: ) Why did they move in opposite directions? 2) Which particle had the more curved path and why?

20 13/04/2015 Deflection by Magnetic Fields Recall: protons, 2 neutrons, therefore charge = +2 1 electron, therefore charge = -1 Because of this charge, they will also be deflected by magnetic fields: Region of magnetic field 1) Why did they move in opposite directions? 2) Which particle had the more curved path and why?

21 13/04/2015 Uses of radioactivity 1 Sterilising medical instruments Gamma rays can be used to kill and sterilise germs without the need for heating. The same technique can be used to kill microbes in food so that it lasts longer.

22 13/04/2015 Uses of radioactivity 2 - Tracers A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe: Gamma source Tracers can also be used in medicine to detect tumours: The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected. For medicinal tracers, you would probably use a beta source with a short half life – why?

23 13/04/2015 Uses of radioactivity 3 – Smoke Detectors Smoke detectors Alarm +ve electrode -ve electrode Alpha emitter Ionised air particles If smoke enters here a current no longer flows

24 13/04/2015 Uses of Radioactivity 4 - Treating Cancer High energy gamma radiation can be used to kill cancerous cells. However, care must be taken in order to enure that the gamma radiation does not affect normal tissue as well. Radioactive iodine can be used to treat thyroid cancer. Iodine is needed by the thyroid so it naturally collects there. Radioactive iodine will then give out beta radiation and kill cancerous cells.

25 13/04/2015 Dangers of radioactivity OUTSIDE the body  and  are more dangerous as  radiation is blocked by the skin. INSIDE the body an  source causes the most damage because it is the most ionising. Alpha Beta Radiation will ionise atoms in living cells – this can damage them and cause cancer or leukaemia. Gamma

26 13/04/2015 Half life The decay of radioisotopes can be used to measure the material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay… At start there are 16 radioisotopes After 1 half life half have decayed (that’s 8) After 3 half lives another 2 have decayed (14 altogether) After 2 half lives another half have decayed (12 altogether) = radioisotope= new atom formed

27 13/04/2015 A radioactive decay graph Time Count 1 half life

28 13/04/2015 Dating materials using half-lives Question: Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. 8 8 Answer: The sample was originally completely uranium… …of the sample was uranium Now only 4/8 of the uranium remains – the other 4/8 is lead Now only 2/8 of uranium remains – the other 6/8 is lead Now only 1/8 of uranium remains – the other 7/8 is lead So it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,000,000,000 years so the sample is 12,000,000,000 years old. 1 half life later…

29 13/04/2015 An exam question… Potassium decays into argon. The half life of potassium is 1.3 billion years. A sample of rock from Mars is found to contain three argon atoms for every atom of potassium. How old is the rock? (3 marks) The rock must be 2 half lives old – 2.6 billion years

30 13/04/2015 P2.6.1 – Nuclear Fission

31 13/04/2015 Nuclear fission Uranium or plutonium nucleus Unstable nucleus New nuclei (e.g. barium and krypton) More neutrons Neutron

32 13/04/2015 Chain reactions Each fission reaction releases neutrons that are used in further reactions.

33 13/04/2015 Nuclear power stations Nuclear power stations use the energy from each reaction to heat water and use the steam to drive turbines:

34 13/04/2015 P2.6.2 – Nuclear Fusion

35 13/04/2015 Nuclear Fusion in stars ProtonNeutron Nuclear fusion happens in stars but it’s not possible to use it in power stations yet as it needs temperatures of around 10,000,000 O C

36 13/04/2015 The Life Cycle of a Star

37 13/04/2015 Stage 1: Nebulae A nebulae is a collection of dust, gas and rock. Some examples of nebulae…

38 13/04/2015 Dark nebula

39 13/04/2015 Emission nebula

40 13/04/2015 Reflection nebula

41 13/04/2015 Planetary nebula (This nebula is smaller and will only form a planet)

42 13/04/2015 Gravity will slowly pull these particles together… As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed Stage 2: Protostar

43 13/04/2015 Stage 3: Main Sequence Our sun is an example of a main sequence star – it’s in the middle of a 10 billion year life span In a main sequence star the forces of attraction pulling the particles inwards are _________ by forces acting outwards due to the huge __________ inside the star. Stars are basically ________ reactors that use _______ as a fuel. During its main sequence a star will release energy by converting hydrogen and helium (light elements) into _________ elements and this is why the universe now contains a number of heavier elements. Words – heavier, balanced, hydrogen, nuclear, temperatures

44 13/04/2015 Eventually the hydrogen and helium will run out. When this happens the star will become colder and redder and start to swell… If the star is relatively small (like our sun) the star will become a RED GIANT If the star is big (at least 4 times the size of our sun) it will become a RED SUPERGIANT Stage 4: Red Giant

45 13/04/2015 What happens at this point depends on the size of the star… 1) For SMALL stars the red giant will collapse under its own gravity and form a very dense white dwarf: Stage 5: The Death White dwarfBlack dwarf Red giant

46 13/04/2015 2) If the star was a RED SUPERGIANT it will shrink and then EXPLODE, releasing massive amounts of energy, dust and gas. AfterBefore This explosion is called a SUPERNOVA

47 13/04/2015 The dust and gas on the outside of the supernova are thrown away by the explosion and the remaining core turns into a NEUTRON STAR. If the star is big enough it could become a BLACK HOLE instead.

48 13/04/2015 The dust and gas thrown out by a supernova can be used to form a new star… Stage 6: Second generation stars Our sun is believed to be a “______ ______ star” – this is because it contains some __________ elements along with hydrogen and ________. These heavier elements would have been the products of a previous star that have been thrown out by a ________. These heavier elements are also found on planets, indicating that they might have been made from remains of previous _______ as well. Words – helium, heavier, second generation, stars, supernova

49 13/04/2015 The Life Cycle of a Star summary Protostar Main sequence Red super giant Supernova Red giant White dwarf Black dwarfNeutron starBlack hole Basically, it all depends on the size of the star! SMALL stars BIG stars

50 13/04/2015 This slideshow has been made freely available on the TES Resources website. More Science PowerPoints like this can be found at the website This site contains slideshows that cover the 2011 AQA, EdExcel, OCR Gateway and OCR 21st Century courses (with more material being added every year) and A Level Physics and KS3 Some slideshows are free, others require a small subscription fee to be taken out (currently only £50 for a year). Further details can be found at Education Using PowerPoint.Education Using PowerPoint

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