P 3 Contents

1. How to Operate This PowerPoint Select slideshow and click on “From Beginning”. Click once and this box will disappear, then choose the section you wish to look at and click on next to it. P3 Contents Sparks Uses of Electrostatics Safe Electricals Ultrasound What is Radioactivity? Uses of Radioisotopes Radiation Treatment Fission and Fusion

2. P4: Radiation For Life Sparks Learning Objectives All: Be able to describe how items can become charged Most: Be able to explain how static electricity can be generated Some: Be able to recommend safety measures for dealing with static electricity Starter: Complete the true/false questions you have been given

3. What We Know: True or False ? • Good conductors let electricity pass through them • A good conductor is known as an insulator • Metals do not let electricity pass through them • Plastic is an example of an insulator • Charges can be positive, negative or neutral • Ions are neutral atoms • Gaining electrons makes something negative • Losing electrons makes something positive • Like charges attract (e.g. positive and positive) • Opposing charges repel (e.g. positive and negative) • Neutral charges attracts positives and negatives T F F T T F T T F F T

4. Charged by Friction • Some insulators can become charged through friction • When acetate is rubbed with a duster the electrons are transferred into the duster • The acetate loses electrons – it becomes positively charged • The duster gains electrons – it becomes negatively charged REMEMBER – it is just the electrons that move!

5. Shocks • Some dusters are designed to be charged so they attract bits of dust • Other objects can pick up a charge e.g. nylon, synthetic fibres, you • If the charged object touches something that is earthed there can be a shock • The electrons jump to the earthed object – it gives them a way out

6. Static Problems • Static electricity can be a issue in everyday life – sometimes it’s dangerous, sometimes it’s just annoying • Which of these are dangerous, which are annoying? Static electricity near flammable gases or high conc. of O2 Static electricity in clothes, e.g. after being tumble dried Touching something with a large electrostatic charge Static electricity in monitors – TV, computers

7. Static Safety • How can an electrostatic charge be removed safely? • An earth wire can allow a charge to escape • Using insulating mats/shoes • Anti-static cloths, liquids and sprays can prevent a charge being built up

8. P4: Radiation For Life Uses of Electrostatics Learning Objectives All: Be able recall examples of uses of static electricity Most: Be able to example how static electricity can be utilised Some: Be able to compare different uses of static electricity Starter: Which of the items use static electricity

9. Use Electrostatics?

10. Electrostatic Precipitators • These are used to clean the small solid smoke particles (e.g. carbon) from the waste gases produced by factories • If not removed the smoke can damage buildings and affect peoples health (breathing difficulties)

11. Electrostatic Precipitator 4. Smoke particles are attracted to the collecting plates 4 3. Collecting plate – either earthed or positively charged 3 5. Collecting plates are knocked and the particles fall into the collection trays 5 2. Smoke particles gain electrons and become negative 2 1. Metal grid with high voltage passing through – usually negatively charged 1

12. Spray Painting • Static electricity can be used in spraying liquids e.g. spraying pesticides, spray painting • The car gains electrons • The gun looses electrons so the paint looses electrons • The paint spreads out as each positive drop repels • No paint is wasted as the negative car attracts the positive paint Positive spray gun Negative car

13. Spraying • When spraying pesticides or herbicides the liquid can be given a charge and then sprayed either from a vehicle or a plane • The charged droplets repel each other so the distribution is even • The charged droplets are all attracted to the neutral earth and so do not drift away

14. Defibrillators • Defibrillators do not restart someone’s heart • A defibrillator is used to regulate an erratic heartbeat • The two paddles are charged by a high voltage power source and then placed on the patients chest • The charge makes the heart contract • Only the patient should be shocked • This is why they have insulated handles • This is why the user shouts “clear”

15. P4: Radiation For Life Safe Electricals Learning Objectives All: Be able to describe what is needed for electricity to flow Most: Be able to explain the difference between current and resistance Some: Be able to compare fuses and circuit breakers Starter: In which of the circuits will the light work and why?

16. Working Circuits Incomplete circuit Short circuit Working circuit Incomplete circuit

17. Current • Water current What is it? • So, what is Electric current?

18. Electric Current • This is caused by the movement of delocalised electrons • They flow from the negative side of the cell, through the circuit, towards the positive side

19. 1 Coulomb = 6.2415 x1018 electrons What is Current? Welcome to Chaucer = a lump of charge (a Coulomb)

20. Current What is current? What is potential difference (aka voltage)? Rate of flow of charge Symbolised by I Measured in amps (A), often use mA Measured by an ammeter

21. What is Potential Difference? Welcome to Chaucer = Energy

22. Current and Potential Difference What is current? What is potential difference (aka voltage)? Rate of flow of charge Symbolised by I Measured in amps (A), often use mA Measured by an ammeter The difference in energy per unit of charge across a component Symbolised by V Measured in volts (V), Measured by a voltmeter

23. What is it? • You have been given some circuit symbols – some you should know, some you might not • Below are the names of the symbols but not in the same order Ammeter Battery Chemical Cell Diode Fuse Heater Lamp Light Dependent Resistor Light Emitting Diode Open Switch Resistor Thermistor Variable Resistor Voltmeter

24. What is it? + - A chemical cell The long thin line is positive The short thick line is negative More than one is called a battery Just to be confusing: Current is shown as flowing from + to -

25. What is it? An open switch A closed switch

26. What is it? A fuse Note the line through the middle, just like a real fuse

27. What is it? A heater

28. What is it? A Light Dependent Resistor (LDR) Note the light rays heading towards the resistor

29. What is it? Lamp

30. What is it? A variable resistor Note the arrow showing that the resistance can alter

31. What is it? An ammeter

32. What is it? A diode Controls the DIrection of current.

33. What is it? A resistor

34. What is it? A thermistor (heat dependent resistor) Note the line (similar to that on a graph) showing increasing current (decreasing resistance) with increasing temperature

35. What is it? An voltmeter

36. What is it? A Light Emitting Diode (LED) Note the light rays heading away from the diode

37. Current and Potential Difference What is current? What is potential difference (aka voltage)? Rate of flow of charge Symbolised by I Measured in amps (A), often use mA Measured by an ammeter The difference in energy per unit of charge across a component Symbolised by V Measured in volts (V), Measured by a voltmeter

38. Resistance • What is resistance? • A thicker wire will have more/less resistance • A longer wire will have more/less resistance How difficult it is for the charge (the electrons) to pass through Symbolised by R Measured in ohms (Ω) Is found using Ohms Law

39. Measuring Resistance • For a specific resistance increasing the potential difference will increase the current • For a specific potential difference increasing the resistance will decrease the current • This relationship is known as Ohms Law • By using resistors and variable resistors (rheostats) it is possible to control the amount of current in a circuit

40. Ohm’s Law Potential Difference OHMS LAW: The voltage is directly proportional to current across a resistor at a constant temperature • By using resistors and variable resistors (rheostats) it is possible to control the amount of current in a circuit Resistance Current Resistance = Potential Difference (V) (Ω) Current (A) • Now try and rearrange this to work out the equations for potential difference and current

41. Ohm’s Law V Potential Difference I R Resistance Current Resistance = Potential Difference (V) (Ω) Current (A) Potential Difference = Resistance x Current (V) (Ω) (A) Current = Potential Difference (V) (A) Resistance (Ω)

42. Ohms Law V Potential Difference I R Example: The current through a wire is 2.0A when the potential difference across it is 12V. What is the resistance? Resistance Current What we know: I = 2.0 V = 12 Resistance = Potential Difference = V Current I Resistance = 12 2 = 6.0 Ω

43. Ohms Law V Potential Difference I R 1. Current: 6A Potential Difference: 18V What is the resistance? 2. Resistance: 32Ω Potential Difference: 8V What is the current? 3. Current: 0.4A Resistance: 15Ω What is the potential difference? Resistance Current R = V = 18 = 3Ω I 6 I = V = 8 = 0.25A R 32 V = I x R = 0.4 x 15 = 6v

44. Fill in the Blank • Current is the rate of flow of charge per second • Current is measured in amps and is symbolised by I • Potential Difference is the difference in the size of charge at two points in the circuit • Potential Difference is measured in volts and is symbolised by V • Resistance is how difficult it is for the charge to pass through a component • Resistance is measured in ohms • Resistance = A B C D E F Potential Difference Current G

45. What is it? An ammeter A voltmeter A resistor

46. What is it? A diode A cell A battery

47. What is it? A fuse A switch A variable resistor

48. What is it? A switch A LED A LDR

49. What is it? A fuse A thermistor A resistor

50. What is it? A lamp A diode A cell