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OCR Additional Science

OCR Additional Science. Radiation for Life Revision PowerPoint! V. Static Electricity. +. -. -. +. Static electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used:. +. +. -. -. +. +. +. -. -. -. +.

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OCR Additional Science

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  1. OCR Additional Science Radiation for Life Revision PowerPoint! V

  2. Static Electricity + - - + Static electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used: + + - - + + + - - - + + - + - -

  3. Static Electricity - - + - - + + - - - - -

  4. Van de Graaf generators

  5. Use of static - Photocopiers 1) + + + + + + + + + + P P P + + 2) + + + 3+4) P + + + + + P Photocopiers use static electricity. They work by: 1) Copying an ______ of the page onto a ______ plate, 2) Light then causes the charge to ____ away, leaving an “electrostatic impression” of the page, 3) The charges left on the plate ______ small drops of black powder, 4) The powder is transferred from the plate onto the _____, 5) The paper is _____ to “fix” the powder. Words – heated, leak, paper, image, charged, attract

  6. Uses of Static – Smoke Precipitators Chimney Negatively charged plates - - - - - - Positively charged grid + + +

  7. Uses and dangers of Static Electricity Find out how static electricity is used in the following: 1) Laser printers 2) Paint sprayer 3) Defibrillators Find out how static electricity is dangerous in the following situations: 1) Fuel pipes 2) Hospitals

  8. Wiring a plug 1. 4. 5. 2. 6. 3. Earth wire Live wire Fuse Neutral wire Cable grip Insulation The neutral wire of a plug stays at a potential close to zero relative to the Earth The live wire of a plug alternates between positive and negative potential relative to the Earth

  9. Fuses Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____. Words – large, harm, safety, melt, live, circuit, fuse

  10. Earth wires Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows. Words – fuse, fault, metal, surges, touch

  11. Circuit breakers Residual Current Circuit Breakers (RCCBs) are often used with fuses. They have some advantages over fuses: • They are safer – they don’t get hot • They react more quickly • They can be switched off for repairs • They are easy to reset • Each RCCB is attached to a certain circuit, so if one switches off you can see which circuit has a fault

  12. Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. Georg Simon Ohm 1789-1854 V Resistance = Voltage (in V) (in ) Current (in A) I R The resistance of a component can be calculated using Ohm’s Law:

  13. An example question: Ammeter reads 2A A V Voltmeter reads 10V • What is the resistance across this bulb? • Assuming all the bulbs are the same what is the total resistance in this circuit?

  14. Resistance Resistance (Ohms, ) = Potential Difference (volts, V) Current (amps, A) Resistance is anything that opposes an electric current. • What is the resistance of the following: • A bulb with a voltage of 3V and a current of 1A. • A resistor with a voltage of 12V and a current of 3A • A diode with a voltage of 240V and a current of 40A • A thermistor with a current of 0.5A and a voltage of 10V

  15. Waves- Some definitions… 1) Amplitude – this is “how high” the wave is: 2)Wavelength ()– this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)

  16. Some definitions… Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave…

  17. Ultrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. It can be used in pre-natal scanning: How does it work? Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object. Words – depth, reflected, picture, medium

  18. Other uses of ultrasound 1) Echo sounding The ultrasound is reflected from the sea floor. 2) Breaking down kidney stones Ultrasonic waves break kidney stones into much smaller pieces 3) Cleaning (including teeth) Ultrasound causes dirt to vibrate dirt off without damaging the object

  19. The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

  20. The structure of the atom MASS NUMBER = number of protons + number of neutrons 4 He SYMBOL 2 PROTON NUMBER = number of protons (obviously)

  21. Introduction to Radioactivity Some substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation: Radiation The nucleus is more stable after emitting some radiation – this is called “radioactice decay” and the activity is measured in “Becquerels (Bq)”.

  22. Types of radiation New nucleus 1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom) Unstable nucleus New nucleus Alpha particle 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. Beta particle Unstable nucleus 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. Words – frequency, proton, energy, neutrons, helium, beta Unstable nucleus New nucleus Gamma radiation

  23. Changes in Mass and Proton Number 241 237 4 α Am Np + 95 93 2 90 90 0 β Sr Y + -1 38 39 Alpha decay: Beta decay:

  24. Uses of radioactivity 1 Sterilising medical instruments Gamma rays can be used to kill and sterilise germs without the need for heating.

  25. Uses of radioactivity 2 Beta detector Paper Rollers Beta emitter

  26. Uses of radioactivity 3 Alpha emitter +ve electrode -ve electrode If smoke enters here a current no longer flows Ionised air particles Smoke detectors Alarm

  27. 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.

  28. Half life = radioisotope = new atom formed 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… After 2 half lives another half have decayed (12 altogether) After 3 half lives another 2 have decayed (14 altogether) After 1 half life half have decayed (that’s 8) At start there are 16 radioisotopes

  29. A radioactive decay graph 1 half life 1 half life 1 half life Count Time

  30. Dating materials using half-lives 1 half life later… 1 half life later… 1 half life later… 2 1 8 4 8 8 8 8 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. 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.

  31. 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

  32. Background Radiation 13% are man-made Radon gas Food Cosmic rays Gamma rays Medical Nuclear power

  33. Uses of radioisotopes - tracers Gamma source A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe: The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected. Tracers can also be used to develop better plant fertilisers and in medicine to detect tumours:

  34. Nuclear power stations Nuclear fuel is used to boil water in a “heat exchanger” These work by using nuclear fission reactions using uranium:

  35. Nuclear fission More neutrons Neutron Unstable nucleus Uranium or plutonium nucleus New nuclei (e.g. barium and krypton)

  36. Chain reactions Each fission reaction releases neutrons that are used in further reactions.

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