1. OCR Additional Science
15/11/2018
OCR Additional Science
Radiation for Life
Revision PowerPoint! V

2. Static Electricity + + - - + - + + + - - - + + - + - -
15/11/2018
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
15/11/2018 + - - -

4. Van de Graaf generators
15/11/2018

5. Use of static - Photocopiers
15/11/2018 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. P + 2)
3+4) P +
Words – heated, leak, paper, image, charged, attract

6. Uses of Static – Smoke Precipitators
15/11/2018
Chimney
Negatively charged plates - - - - - -
Positively charged grid + + +

7. Uses and dangers of Static Electricity
15/11/2018
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. Earth wire 4. Live wire 5. Fuse 2. Neutral wire 6.
15/11/2018 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

9. Words – large, harm, safety, melt, live, circuit, fuse
Fuses
15/11/2018
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. Words – fuse, fault, metal, surges, touch
Earth wires
15/11/2018
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
15/11/2018
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 V R I Resistance = Voltage (in V) (in ) Current (in A)
Georg Simon Ohm
15/11/2018
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)

13. An example question: Ammeter reads 2A A V
15/11/2018
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

14. Resistance Resistance is anything that opposes an electric current.
15/11/2018
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

15. Waves- Some definitions…
15/11/2018
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…
15/11/2018
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. Words – depth, reflected, picture, medium
Ultrasound
15/11/2018
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
15/11/2018
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
15/11/2018
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
15/11/2018
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)

21. Introduction to Radioactivity
15/11/2018
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
15/11/2018
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

23. Changes in Mass and Proton Number
15/11/2018
Alpha decay: Am
241 95 Np
237 93 α 4 2 +
Beta decay: Sr 90 38 Y β -1 + 90 39

24. Uses of radioactivity 1 Sterilising medical instruments
15/11/2018
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 Rollers Paper Beta emitter
15/11/2018
Beta detector
Rollers
Paper
Beta emitter

26. If smoke enters here a current no longer flows
Uses of radioactivity 3
15/11/2018
Smoke detectors
Alpha emitter
+ve electrode
-ve electrode
Alarm
Ionised air particles
If smoke enters here a current no longer flows

27. Uses of Radioactivity 4 - Treating Cancer
15/11/2018
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
15/11/2018
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

29. A radioactive decay graph
15/11/2018
Count
1 half life
1 half life
1 half life
Time

30. Dating materials using half-lives
15/11/2018
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.

31. An exam question…
15/11/2018
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
15/11/2018
13% are man-made
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power

33. Uses of radioisotopes - tracers
15/11/2018
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.
Tracers can also be used to develop better plant fertilisers and in medicine to detect tumours:

34. Nuclear power stations
15/11/2018
These work by using nuclear fission reactions using uranium:
Nuclear fuel is used to boil water in a “heat exchanger”

35. Nuclear fission More neutrons Neutron Uranium or plutonium nucleus
15/11/2018
More neutrons
Neutron
Uranium or plutonium nucleus
Unstable nucleus
New nuclei (e.g. barium and krypton)

36. Chain reactions
15/11/2018
Each fission reaction releases neutrons that are used in further reactions.