Radiation for Life OCR Additional Science

Transcription

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

2 P4a: Sparks

3 Static Electricity An introduction click here

4 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:

5 Short Static Experiments Try the following quick static electricity experiments: 1) Rubbing a balloon on your jumper and sticking it to the wall 2) Charging a plastic rod by rubbing it with a cloth and then holding it near the water from a smooth-running tap 3) Charging a plastic rod and trying to pick up small pieces of paper (or someone else s hair!) with it 4) 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

7 Static Electricity in Lightning e - e - e - e -

8 Van de Graaf generators 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

10 P4b: Uses of Electrostatics

11 Using Static in Paint Sprayers Connected to negative voltage Connected to positive voltage 1) Why is the paint sprayer given a negative charge? 2) Why is the car given a positive charge?

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

13 Uses of Static - Defibrillators How do defibrillators work?

14 P4c: Safe Electricals

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

16 Resistance 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: Resistance = Voltage (in V) (in ) Current (in A) I Georg Simon Ohm V R

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

18 More examples 3A 6V 12V 3A 4V 2A 1A 2V What is the resistance of these bulbs?

19 Resistance 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

20 Wiring a plug 1. Earth wire 4. Live wire 2. Neutral wire 5. Fuse 3. Insulation 6. Cable grip 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 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

22 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

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

24 Power and fuses Power is the rate of doing work. The amount of power being used in an electrical circuit is given by: P Power = voltage x current in W in V in A V I 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 Power rating (W) Voltage (V) Toaster Fire Hairdryer Hoover Computer Stereo Current needed (A) Fuse needed (3, 5 or 13A)

26 Power and fuses Copy and complete the following table: Appliance Power rating (W) Voltage (V) Current needed (A) Fuse needed (3, 5 or 13A) Toaster Fire Hairdryer Hoover Computer or 1 Stereo or 1

27 P4d: Ultrasound

28 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)

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

30 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

31 Other uses of ultrasound 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?

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

34 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).

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

36 Changes in Mass and Proton Number Alpha decay: Am Np α Beta decay: Sr Y + β

37 Ionisation 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 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 At start there are 16 radioisotopes After 1 half life half have decayed (that s 8) After 2 half lives another half have decayed (12 altogether) After 3 half lives another 2 have decayed (14 altogether)

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

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

41 P4f: Uses of Radioisotopes

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

43 Background Radiation by Location 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 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 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 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 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 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 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 P4g: Treatment

50 X-Rays and Gamma Rays 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 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 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 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 Exposure to Radiation 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 P4h: Fission and Fusion

56 How Power Stations Work 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 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 Unstable nucleus New nuclei (e.g. barium and krypton)

59 Chain reactions 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 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 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 10,000,000 O C and very high pressures.

62 Cold Fusion 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.