Physics part 1 static electricity new.ppt
- 1. © Boardworks Ltd 2005 1 of 45 Electric charge or Static Electricity
- 2. © Boardworks Ltd 2005 2 of 45 Static Electricity Static charge Forces between charges Electrolysis Summary activities Uses of static electricity Contents
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- 9. © Boardworks Ltd 2005 9 of 45 Where does static charge come from? All materials are made of atoms, which contain electric charges. Around the outside of an atom are electrons, which have a negative charge. The nucleus at the centre of an atom contains protons which have a positive charge. An atom has equal amounts of negative and positive charges which cancel each other out. This means an atom has no overall charge. Electrons do not always stay attached to atoms and can sometimes be removed by rubbing. electron (negative charge) proton (positive charge)
- 10. © Boardworks Ltd 2005 10 of 45 How does static charge build up? Static charge can build up when two materials are rubbed together, such as a plastic comb moving through hair. When this happens electrons are transferred from one material to the other: One material ends up with more electrons, so it now has an overall negative charge. One material ends up with fewer electrons, so it now has an overall positive charge.
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- 14. © Boardworks Ltd 2005 14 of 45 If an insulator made of polythene is rubbed with a cloth, electrons move from the cloth to the insulator. The cloth is positively charged. The insulator is negatively charged. What charge does the cloth now have? What charge does the polythene insulator now have? Charging polythene
- 15. © Boardworks Ltd 2005 15 of 45 If an insulator made of acetate is rubbed with a cloth, electrons move from the insulator to the cloth. Charging acetate The cloth is negatively charged. The insulator is positively charged. What charge does the cloth now have? What charge does the polythene insulator now have?
- 16. © Boardworks Ltd 2005 16 of 45 Static charge – true or false?
- 17. © Boardworks Ltd 2005 17 of 45 CLASS WORK Answer the following questions: 1.Describe the structure of an atom. 2.Differentiate between electrical conductors and insulators with examples. 3.Draw diagrams to show the charge distribution for charged(positively & negatively)and uncharged objects. 4.Explain in detail, how insulating materials can be charged by friction with the help of a diagram.
- 18. © Boardworks Ltd 2005 18 of 45 Static Electricity Static charge Forces between charges Electrolysis Summary activities Uses of static electricity Contents
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- 21. © Boardworks Ltd 2005 21 of 45 Pairs of charges – attract or repel?
- 22. © Boardworks Ltd 2005 22 of 45 Identifying an unknown charge If the unknown charge is brought near to a positively charged rod and it is attracted to this rod, then the unknown charge must be ________. If the unknown charge is brought near to a positively charged rod and it is repelled by this rod, then the unknown charge must be ________. negative positive ? If a rod has an unknown charge, how can the unknown charge be identified using a positively charged rod?
- 23. © Boardworks Ltd 2005 23 of 45 Identifying an unknown charge If the unknown charge is brought near to a negatively charged rod and it is attracted to this rod, then the unknown charge must be ________. If the unknown charge is brought near to a negatively charged rod and it is repelled by this rod, then the unknown charge must be ________. positive negative ? If a rod has an unknown charge, how can the unknown charge be identified using a negatively charged rod?
- 24. © Boardworks Ltd 2005 24 of 45 + - + - + - + - + - + - + - + - + - If a negatively charged rod is brought near to a piece of paper, the paper sticks to the rod. The paper is uncharged (equal amounts of + and -), so why does it stick to the rod? As the negatively charged rod approaches the paper, the electrons in the paper are repelled away from the rod. This makes one side of the paper positive and one side negative. A charge has been induced on the paper and the positive side of the paper is attracted to the negative rod. Inducing a temporary charge
- 25. © Boardworks Ltd 2005 25 of 45 + - + - + - + - + - + - + - + - + - If a positively charged rod is brought near to a piece of paper, the paper sticks to the rod. The paper is uncharged (equal amounts of + and -), so why does it stick to the rod? As the positively charged rod approaches the paper, a charge has been induced on the paper the electrons and the negative side of the paper is attracted to the positive rod. This makes one side of the paper negative and one side positive as like charges repel and unlike charges attract.The force of attraction between the positive charges on the rod and the negative charges on the paper is greater than the force of repusion between the positive charges on the rod and the positive charges on the paper.So the paper gets attracted to the charged rod. Inducing a temporary charge
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- 27. © Boardworks Ltd 2005 27 of 45 The gold leaf electroscope
- 28. © Boardworks Ltd 2005 28 of 45 Static Electricity Static charge Forces between charges Electrolysis Summary activities Uses of static electricity Contents
- 29. © Boardworks Ltd 2005 29 of 45 Static electricity can be dangerous but it can also be useful, as long as it is used carefully. Examples of uses of static electricity are: 1. ___________________ 2. ___________________ 3. ___________________ 4. Electrostatic precipitators or___________________ Photocopiers Inkjet Printers Spray painting Pollutant removers Uses of static electricity
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- 31. © Boardworks Ltd 2005 31 of 45 Photocopier activity
- 32. © Boardworks Ltd 2005 32 of 45 Inkjet Printers
- 33. © Boardworks Ltd 2005 33 of 45 An electrostatic paint spray The nozzle of the paint gun is connected to one terminal of an electrostatic generator. The other terminal is connected to the metal panel, which is earthed. - - - - - - - - - Paint gun nozzle has a positive charge. Car is negatively charged. + electrostatic generator Static electricity can be used to spray a car with paint: - - - - - -
- 34. © Boardworks Ltd 2005 34 of 45 An electrostatic paint spray The spray gun is designed to produce tiny charged droplets of paint.The drops of paint that emerge from the spray gun are charged.As the drops all carry the same charge they repel and spread out forming a thin spray. The car panel has a wire attached to an electrical supply giving the panel positive charge. As unlike charges attract, the charged droplets are attracted to the car body panel. This gives a uniform coating of paint. Also, the droplets travel along the lines of force of the electrostatic field to reach hidden parts of the panel. - - Paint gun nozzle has a positive charge. Car is negatively charged. electrostatic generator - - - - - - - - - - - - - - + + + + +
- 35. © Boardworks Ltd 2005 35 of 45 Electrostatic Precipitators: Many heavy industrial plants, such as steel-making furnaces and coal-fired power stations, produce large quantities of smoke. This smoke carries small particles of ash and dust into the environment, causing health problems and damage to buildings. One way of removing these pollutants from the smoke is to use electrostatic precipitators. Fig: Electrostatic precipitators help to cut down the amount of pollution released into the atmosphere. As the smoke initially rises up the chimney, it passes through a mesh of wires that are highly charged. (The wires are at a voltage of approximately- 50 000 V.) As they pass through the mesh, the ash and dust particles become negatively charged. Higher up the chimney, these charged particles are attracted by and stick to, large metal earthed plates. The cleaner smoke is then released into the atmosphere. When the earthed plates are completely covered with dust and ash, they are tapped hard. The dust and ash fall into collection boxes, which are later emptied. In a large coal-fired power station,50--60 tonnes of dust and ash may be removed from the smoke each hour!
- 36. © Boardworks Ltd 2005 36 of 45 What are the dangers of static electricity?
- 37. © Boardworks Ltd 2005 37 of 45 Dangers of static charge Filling fuel, rollers for paper and grain shoots are situations where charge can be a problem.
- 38. © Boardworks Ltd 2005 38 of 45 The relationship between charge, current and time is shown by the equation: Charge is measured in coulombs (C). Current is measured in amps (A). Time is measured in seconds (s). Charge, current and time charge = current x time Q = I x t What are the units of charge, current and time?
- 39. © Boardworks Ltd 2005 39 of 45 Q I t x A formula triangle helps you to rearrange a formula. The formula triangle for Q = It is shown below. Whatever quantity you are trying to find, cover it up and this will leave the formula required. So if you are trying to find current (I)... …cover up I… …which gives the formula… Q = It formula triangle I = Q t
- 40. © Boardworks Ltd 2005 40 of 45 charge = current x time = 6A x (3 x 60)s = 1080C TOP TIP: Always remember to convert time into seconds! A current of 6A flows for 3 minutes. How much charge flows in that time? Using Q = It
- 41. © Boardworks Ltd 2005 41 of 45 Energy, charge and voltage The relationship between energy, charge and potential difference (or voltage) is shown by the equation: energy = charge x voltage E = Q x V What are the units of energy, charge and voltage? Energy is measured in joules (J). Charge is measured in coulombs (C). Voltage measured in volts (V).
- 42. © Boardworks Ltd 2005 42 of 45 E Q V x A formula triangle helps you to rearrange a formula. The formula triangle for E = QV is shown below. Whatever quantity you are trying to find, cover it up and this will leave the formula required. So if you are trying to find charge (Q)... …cover up Q… …which gives the formula… E = QV formula triangle Q = E V
- 43. © Boardworks Ltd 2005 43 of 45 Using the E = QV formula triangle
- 44. © Boardworks Ltd 2005 44 of 45 energy = charge x voltage = 100C x 5V = 500J TOP TIP: In exams, you must always give the units. If you do not, you will lose a mark! What is 500J in kJ? 0.5 kJ A charge of 100C is delivered at a potential difference of 5V. How much energy is delivered? Using E = QV
- 45. © Boardworks Ltd 2005 45 of 45 Charge calculations