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# OCR Additional Science

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OCR Additional Science
11/04/2017 OCR Additional Science P4 Radiation for Life AGAC

Equations for this unit (Foundation)
11/04/2017 Equations for this unit (Foundation) unit 5 unit6

the equations needed for this
11/04/2017 unit 5 This slide shows the equations needed for this Unit (Higher) unit6

Static Electricity + + - - + - + + + - - - + + - + - -
11/04/2017 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: Rod becomes negatively charged Rod becomes positively charged + + - - + - + + + - - - + + - + - - It is only the negative charges -the electrons which move

F 11/04/2017 attracted to duster positive negative

H 11/04/2017 Any three from: Duster has gained electrons
Dust is positively charged Dust has lost electrons Opposite charges attract

Unlike charges attract
Static Electricity 11/04/2017 + - Unlike charges attract - - Like charges repel

Van de Graaf generators
11/04/2017

Use of static - Photocopiers
11/04/2017 P + 1) 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. image charged leak P + 2) attract 3+4) P + paper heated Words – heated, leak, paper, image, charged, attract

Uses of Static – Smoke Precipitators
11/04/2017 Chimney Negatively charged plates - - - - - - Positively charged grid + + +

Uses and dangers of Static Electricity
11/04/2017 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

H 11/04/2017 These need to be opposites positive/negative
negative/positive attracted knocked

11/04/2017 F shock or sparks

Wiring a plug 1. Earth wire 4. Live wire 5. Fuse 2. Neutral wire 6.
11/04/2017 1. 2. 3. 4. 5. 6. 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

Words – large, harm, safety, melt, live, circuit, fuse
Fuses 11/04/2017 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 _____. safety live large fuse melt circuit harm Words – large, harm, safety, melt, live, circuit, fuse

Words – fuse, fault, metal, surges, touch
Earth wires 11/04/2017 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. metal fault touch surges fuse Words – fuse, fault, metal, surges, touch

Circuit breakers 11/04/2017 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

Resistance V R I Resistance = Voltage (in V) (in ) Current (in A)
Georg Simon Ohm 11/04/2017 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: V R I Resistance = Voltage (in V) (in ) Current (in A)

An example question: Ammeter reads 2A A V
11/04/2017 Ammeter reads 2A V A What is the resistance across this bulb? Assuming all the bulbs are the same what is the total resistance in this circuit? Voltmeter reads 10V

What is the resistance of these bulbs?
More examples… 11/04/2017 3A 6V 12V 4V 2A 1A 2V 3A What is the resistance of these bulbs?

Resistance Resistance is anything that opposes an electric current.
11/04/2017 Resistance is anything that opposes an electric current. Resistance (Ohms, ) = Potential Difference (volts, V) Current (amps, A) 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

11/04/2017 F

H 11/04/2017 Break in the circuit 12/1.5 (1) =8

Waves- Some definitions…
11/04/2017 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)

Some definitions… 11/04/2017 Transverse waves are when the displacement is at right angles to the direction of the wave… Just pick out one particle and follow its motion Longitudinal waves are when the displacement is parallel to the direction of the wave… Just pick out one particle and follow its motion

Words – depth, reflected, picture, medium
Ultrasound 11/04/2017 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. reflected medium depth picture Words – depth, reflected, picture, medium

Other uses of ultrasound
11/04/2017 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

F 11/04/2017 scans to monitor pregnancy break down kidney stones
by vibrating particles measure blood flow by measuring frequency change cleaning instruments makes dirt particles shake off treat cancer using an intense beam aimed at tumour

H 11/04/2017 frequency vibrate break up

The structure of the atom
11/04/2017 ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

The structure of the atom
11/04/2017 Particle Relative Mass Relative Charge Proton 1 +1 Neutron Electron -1 MASS NUMBER = number of protons + number of neutrons He 2 4 SYMBOL PROTON NUMBER = number of protons (obviously)

Introduction to Radioactivity
11/04/2017 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)”.

Types of radiation 11/04/2017 1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom) neutrons Unstable nucleus New nucleus Alpha particle helium 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. proton beta Beta particle New nucleus 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. energy frequency Words – frequency, proton, energy, neutrons, helium, beta Unstable nucleus New nucleus Gamma radiation

Changes in Mass and Proton Number
11/04/2017 Alpha decay: Am 241 95 Np α 4 2 + 237 93 Beta decay: Sr 90 38 Y β -1 + 90 39

Uses of radioactivity 1 Sterilising medical instruments
11/04/2017 Sterilising medical instruments Gamma rays can be used to kill and sterilise germs without the need for heating.

Uses of radioactivity 2 Beta detector Rollers Paper Beta emitter
11/04/2017 Beta detector Rollers Paper Beta emitter This is used to make sure the paper/steel is the correct thickness. The pressure on the rollers is adjusted depending on how much of the beta is received by the detector

Uses of radioactivity 3 Smoke detectors Alpha emitter +ve electrode
11/04/2017 Smoke detectors Alpha emitter +ve electrode -ve electrode Alarm Ionised air particles If smoke enters here a current no longer flows This sets off an alarm This involves `a NOT gate See Unit 6

Uses of Radioactivity 4 - Treating Cancer
11/04/2017 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.

11/04/2017 F / / / /

11/04/2017 F tracer decreases nucleus

H 11/04/2017 all of tumour receives the full dose
focussed/directed at/concentrated all of tumour receives the full dose Healthy tissue does not receive the full dose

H 11/04/2017 so gamma can reach the surface
low count rate after the blockage

Half life 11/04/2017 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… = radioisotope = new atom formed 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

A radioactive decay graph
11/04/2017 Count 1 half life 1 half life 1 half life Time

Dating materials using half-lives
11/04/2017 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… 1 half life later… 1 half life later… 1 half life later… 8 4 8 2 8 1 8 …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.

An exam question… 11/04/2017 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

Background Radiation 13% are man-made Radon gas Food Cosmic rays
11/04/2017 13% are man-made Radon gas Food Cosmic rays Gamma rays Medical Nuclear power

Uses of radioisotopes - tracers
11/04/2017 A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe: If there is a blockage we know where it is because there will be no gamma reading beyond it Gamma source 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:

Nuclear power stations
11/04/2017 These work by using nuclear fission reactions using uranium: Nuclear fuel (uranium) is used to boil water in a “heat exchanger”. The steam drives a turbine.

11/04/2017 F uranium produce steam

Nuclear fission More neutrons Neutron Uranium or plutonium nucleus
11/04/2017 More neutrons Neutron Uranium or plutonium nucleus Unstable nucleus New nuclei (e.g. barium and krypton)

Chain reactions 11/04/2017 Each fission reaction releases neutrons that are used in further reactions.

H 11/04/2017 atom/nucleus nucleus neutron absorb neutrons fission

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