1. OCR Additional Science
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Radiation for Life
OCR Additional Science
W Richards
The Weald School

2. 13/11/2018
P4a: Sparks

3. An introduction – click here
Static Electricity
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An introduction – click here

4. Static Electricity + + - - + - + + + - - - + + - + - -
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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: + + - - + - + + + - - - + + - + - -

5. Short Static Experiments
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Try the following quick static electricity experiments:
Rubbing a balloon on your jumper and “sticking” it to the wall
Charging a plastic rod by rubbing it with a cloth and then holding it near the water from a smooth-running tap
Charging a plastic rod and trying to pick up small pieces of paper (or someone else’s hair!) with it
Rubbing a balloon on someone else’s head – you might want to ask their permission first…
Can you explain what you saw in each of these experiments?

6. Static Electricity
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7. Static Electricity in Lightning
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8. Van de Graaf generators
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When a charge is neutralised by the movement of electrons either from the Earth or to the Earth we call this “earthing”

9. Dangers of Static – fuelling lines
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Dangers of Static – fuelling lines

10. P4b: Uses of Electrostatics
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P4b: Uses of Electrostatics

11. Using Static in Paint Sprayers
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Connected to negative voltage
Connected to positive voltage
Why is the paint sprayer given a negative charge?
Why is the car given a positive charge?

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

13. Uses of Static - Defibrillators
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How do defibrillators work?

14. 13/11/2018
P4c: Safe Electricals

15. Electric Current
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Electric current is a flow of negatively charged particles (i.e. electrons).
Note that electrons go from negative to positive - + e-
By definition, current is “the rate of flow of charge” and it is larger through shorter, wider wires e-

16. Resistance V R I Resistance = Voltage (in V) (in ) Current (in A)
Georg Simon Ohm
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Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. Basically, longer wires have more resistance and wider wires have less resistance.
The resistance of a component can be calculated using Ohm’s Law: V R I
Resistance = Voltage (in V)
(in ) Current (in A)

17. An example question: Ammeter reads 2A A V
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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

18. What is the resistance of these bulbs?
More examples…
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12V 4V 2A 1A 2V 3A
What is the resistance of these bulbs?

19. Resistance Resistance is anything that opposes an electric current.
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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 3 4 6
20

20. The neutral wire of a plug is used to complete the circuit.
Wiring a plug
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Earth wire
Live wire
Fuse
Neutral wire
Cable grip
Insulation
The neutral wire of a plug is used to complete the circuit.
The Earth wire of a plug keeps the device safe by stopping the appliance becoming “live”

21. Words – large, harm, safety, melt, live, circuit, fuse
Fuses
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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

22. Circuit breakers
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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

23. Words – fuse, fault, metal, surges, touch
Earth wires
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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. Earth wires are not needed if a device is “double insulated”.
Words – fuse, fault, metal, surges, touch

24. Power and fuses
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Power is “the rate of doing work”. The amount of power being used in an electrical circuit is given by: P I V
Power = voltage x current
in W in V in A
Using this equation we can work out the fuse rating for any appliance. For example, a 3kW (3000W) fire plugged into a 240V supply would need a current of _______ A, so a _______ amp fuse would be used (fuse values are usually 3, 5 or 13A).

25. Power and fuses Copy and complete the following table: Appliance
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Copy and complete the following table:
Appliance
Power rating (W)
Voltage (V)
Current needed (A)
Fuse needed (3, 5 or 13A)
Toaster
920
230
Fire
2000
Hairdryer
300
Hoover
1000
Computer
100
Stereo 80

26. Power and fuses Copy and complete the following table: Appliance
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Copy and complete the following table:
Appliance
Power rating (W)
Voltage (V)
Current needed (A)
Fuse needed (3, 5 or 13A)
Toaster
920
230 4 5
Fire
2000
8.7 13
Hairdryer
300
1.3 3
Hoover
1000
4.3
Computer
100
0.43
3 or 1
Stereo 80
0.3

27. 13/11/2018
P4d: Ultrasound

28. Waves- Some definitions…
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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)

29. Transverse vs. longitudinal waves
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Transverse waves are when the displacement is at right angles to the direction of the wave (e.g. light and other electromagnetic waves)…
Displacement
Direction
Displacement
Longitudinal waves are when the displacement is parallel to the direction of the wave (e.g. sound waves)…
Direction
Where are the compressions and rarefactions?

30. Words – depth, reflected, picture, medium
Ultrasound
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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

31. Other uses of ultrasound
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1) Breaking down kidney stones
Ultrasonic waves break kidney stones into much smaller pieces
2) Cleaning (including teeth)
Ultrasound causes dirt to vibrate dirt off without damaging the object
Why is ultrasound better than X-rays?
Ultrasound can be used instead of X-rays because they are able to produce images of soft tissue and they do not damage living cells.

32. P4e: What is Radioactivity?
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P4e: What is Radioactivity?

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

34. Introduction to Radioactivity
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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)”.

35. Types of radiation
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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
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.
Words – frequency, proton, energy, neutrons, helium, beta
Unstable nucleus
New nucleus
Gamma radiation

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

37. Ionisation
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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.

38. Half life
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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

39. A radioactive decay graph
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Activity (Bq)
“1 Becquerel” means “1 radioactive count per second”
Time

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

41. P4f: Uses of Radioisotopes
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P4f: Uses of Radioisotopes

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

43. Background Radiation by Location
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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

44. Uses of radioisotopes - tracers
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A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe:
Gamma source
The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected.

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

46. Uses of radioactivity – dating rocks
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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.

47. An exam question…
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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

48. Carbon Dating
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The amount of the isotope Carbon-14 present in the air has not changed for thousands of years. Therefore scientists can use it to help calculate how old something is. Consider, for example, a fossilised tree:
1) When the tree died it stopped exchanging carbon-14 with the atmosphere
2) As time went on the amount of carbon-14 decreased as it decayed
3) The amount of current activity can then be compared to a living tree to work out how old it is

49. 13/11/2018
P4g: Treatment

50. X-Rays and Gamma Rays
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X-rays and gamma rays are similar in that they have similar wavelengths and they are both ionising but they are produced in different ways.
Gamma rays are given out from the nucleus of radioactive materials whereas X-rays are made by firing high-speed electrons at metal targets and are therefore easier to control.
X-ray images are possible because the absorption of X-rays depends on the material’s thickness and density.

51. Uses of Radioactivity - sterilisation
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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.

52. Uses of Radioactivity - Treating Cancer
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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.
During radiotherapy gamma rays are focused on the tumour and rotated around the patient with the tumour at the centre, thereby limiting damage to non-canerous tissue.

53. Uses of radioactivity – medical tracers
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As well as using tracers to find leaks in pipes, tracers can also be used in medicine to highlight problem areas within a body by using a radiation detector:
What sort of half life would you want a medical tracer to have?
Medical radioisotopes are produced by placing materials in a nuclear reactor and they become radioactive by absorbing extra neutrons.

54. Radiation dose is measured in units called “sieverts” (Sv).
Exposure to Radiation
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People like me work with radiation a lot so we need to wear a “dosimeter” to record our exposure to radiation:
Radiation dose is measured in units called “sieverts” (Sv).

55. 13/11/2018
P4h: Fission and Fusion

56. How Power Stations Work
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1) A fossil fuel is burned in the boiler
2) Water turns to steam and the steam drives a turbine (in some gas poer stations the air is heated directly)
3) The turbine turns a generator
4) The output of the generator is connected to a transformer
5) The steam is cooled down in a cooling tower and reused

57. Nuclear power stations
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Notice that the heat from these reactions is used to heat water and turn it into steam, which then drives turbines.

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

59. Chain reactions
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Each fission reaction releases neutrons that are used in further reactions. A nuclear bomb is basically a chain reaction that has gone out of control!!

60. Fission in Nuclear power stations
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These fission reactions occur in the fuel rods and they become very hot. Water (a coolant) cools the rods (which then turns to steam) and the control rods are moved in and out to control the amount of fission reactions taking place.

61. Nuclear Fusion in stars
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Proton
Neutron
Nuclear fusion happens in stars but it’s not possible to use it in power stations yet as it needs temperatures of around 10,000,000OC and very high pressures.

62. Stanley Pons and Martin Fleishmann
Cold Fusion
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Stanley Pons and Martin Fleishmann
In 1989 we claimed that we had enabled “cold fusion”, i.e. we had created fusion reactions in lab temperatures. However, no one else could verify our findings so our theories have not been accepted.