07/07/2016 OCR Additional Science Credit to W Richards Radiation for Life

07/07/2016 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:

07/07/2016 Static Electricity

07/07/2016 Van de Graaf generators

07/07/2016 Use of static - Photocopiers 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 P ) ) 3+4)

07/07/2016 Uses of Static – Smoke Precipitators Chimney Negatively charged plates Positively charged grid

07/07/2016 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

07/07/2016 Wiring a plug Earth wire Neutral wire Insulation Live wire Fuse Cable grip The live wire of a plug alternates between positive and negative potential relative to the Earth The neutral wire of a plug stays at a potential close to zero relative to the Earth

07/07/2016Fuses 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

07/07/2016 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

07/07/2016 Circuit breakers Residual Current Circuit Breakers (RCCBs) are often used with fuses. They have some advantages over fuses: 1)They are safer – they don’t get hot 2)They react more quickly 3)They can be switched off for repairs 4)They are easy to reset 5)Each RCCB is attached to a certain circuit, so if one switches off you can see which circuit has a fault

07/07/2016 Georg Simon Ohm Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. The resistance of a component can be calculated using Ohm’s Law: Resistance = Voltage (in V) (in  )Current (in A) V RI

07/07/2016 An example question: V A 1)What is the resistance across this bulb? 2)Assuming all the bulbs are the same what is the total resistance in this circuit? Voltmeter reads 10V Ammeter reads 2A

07/07/2016 More examples… 12V 3A 6V 4V 2A 1A 2V What is the resistance of these bulbs?

07/07/2016Resistance Resistance is anything that opposes an electric current. Resistance (Ohms,  ) = Potential Difference (volts, V) Current (amps, A) What is the resistance of the following: 1)A bulb with a voltage of 3V and a current of 1A. 2)A resistor with a voltage of 12V and a current of 3A 3)A diode with a voltage of 240V and a current of 40A 4)A thermistor with a current of 0.5A and a voltage of 10V

07/07/2016 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)

07/07/2016 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…

07/07/2016Ultrasound 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 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?

07/07/2016 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

07/07/2016 The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

07/07/2016 The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron0 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously)

07/07/2016 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)”.

07/07/2016 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

07/07/2016 Changes in Mass and Proton Number Alpha decay: Am Np α Sr Y β 0 + Beta decay:

07/07/2016 Uses of radioactivity 1 Sterilising medical instruments Gamma rays can be used to kill and sterilise germs without the need for heating.

07/07/2016 Uses of radioactivity 2 Rollers Beta emitter Beta detector Paper

07/07/2016 Uses of radioactivity 3 Smoke detectors Alarm +ve electrode -ve electrode Alpha emitter Ionised air particles If smoke enters here a current no longer flows

07/07/2016 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.

07/07/2016 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

07/07/2016 A radioactive decay graph Time Count 1 half life

07/07/2016 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…

07/07/2016 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

07/07/2016 Background Radiation Radon gas Food Cosmic rays Gamma rays Medical Nuclear power 13% are man-made

07/07/2016 Uses of radioisotopes - 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 to develop better plant fertilisers and 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.

07/07/2016 Nuclear power stations These work by using nuclear fission reactions using uranium: Nuclear fuel is used to boil water in a “heat exchanger”

07/07/2016 Nuclear fission Uranium or plutonium nucleus Unstable nucleus New nuclei (e.g. barium and krypton) More neutrons Neutron

07/07/2016 Chain reactions Each fission reaction releases neutrons that are used in further reactions.