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Electrostatics and Current Electricity

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GCSE Physics Double Award notes

GCSE Physics Double Award notes

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  • 1. Electricity 1 Electrostatics and Current Electricity
  • 2. Aim of the lesson Static charge  3.6.26 recall that insulating materials can be charged by friction and explain this in terms of transfer of charge.  3.6.27 identify that positively charged objects have a deficiency of electrons and negatively charged objects have a surplus of electrons.  3.6.28 describe the dangers and use of electrostatic charge generated in everyday contexts.
  • 3. Text Book Reference  Physics CCEA pg 109-113  Electrostatics is the study of charges at rest
  • 4. Sir Ben Frank  Fly that kite…
  • 5. Electrostatics  The organisation of the parts of an atom has electrons orbiting a large central nucleus of nucleons (neutrons and protons) neutral atom positive ion negative ion These models are NOT to scale
  • 6.  If there is an unbalanced number of protons (positive carriers) compared to electrons (negative carriers) then the ion is called a charged particle - - - ++ ++ ++ - + - + - - + - - 3 electrons, 3 protons- 2 electrons, 3 protons- 4 electrons, 3 protons- no charge positive charge negative charge (deficiency of (surplus of electrons) electrons)
  • 7. Charging by friction In this diagram: The wool and polythene are each ‘uncharged’. What does this mean?
  • 8. Charging by friction The wool is ‘uncharged’, + because… + − − + …it has equal amounts + − + −+− of positive and negative − − charge. + + − −− Equal numbers of + + + and − On the wool On the polythene
  • 9. Charging by friction Equal numbers of + + and − on the wool: + − − + (Count them!) + − + −+− 7+ 7− − − + + − Equal numbers of + −− and − on the polythene: + + (Count them!) 3+ 3−
  • 10. Charging by friction If you rub the wool on +− the polythene, some + − − electrons (−) move from + + +− the wool to the polythene. −+ − − There are now more + + + −− than − on the wool: − + + (Count them!) So now the wool is charged positively, with a surplus of 3 +
  • 11. Charging by friction What has happened to the +− polythene? + − − + + +− There are now more − −+ than + on the polythene: − − (Count them!) + + −− − + + So now the polythene is charged negatively, with a surplus of 3 −
  • 12. Charging by friction This is summed up in the diagram- Both objects are equally charged, with opposite charges because electrons − (only) have moved from the wool to the polythene.
  • 13.  The overall effect of these charged particles produces a force  If the electrical charge is ‘held’ on the surface of a material it is referred to as static electricity.  This type of charge cannot move through out the material (an insulator)  Charged objects exert an electrical force- similar charges repel each other and opposite charges attract.
  • 14.  The electrical static charge can be produced in two ways- by friction and by induction.  The attractive forces which keep the electrons (negative) close to the nucleus (positive) can be easily overcome.  The electrons have relatively low mass compared to the nucleons and therefore it is only ever the electrons which can be transferred throughout a material or from one material to another.
  • 15. Everyday examples of electrostatic Page 111 and 112 Lightning- the bottom of a cloud can be charged by friction of other air particles to produce a large negative + + + + electrostatic charge. This can be discharged on the positively charged - - - - - - - upper surface of another cloud or the positively + + + + + charged ground.
  • 16.  Electrically conductive truck tyres- These tyres drain any charge built up by passing air particles. This safety feature stops any sparks occurring which might prove explosive for any trucks carrying large amounts of fuel.
  • 17. Air Purification- Industries release a huge amount of air pollutants into the atmosphere. Some of the fine dust can be + Positives fixed eliminated by + passing the + + exhaust through + + + charged + Electrons electrostatic plates repelled which attract the Dust particle charged smoke 25000 V 0V particles
  • 18. Aims of the lesson Charge flow  3.6.29 understand that an electric current is a flow of electrons and that it is in the opposite direction to that of a conventional current.  3.6.30 recall that charge is measured in coulombs.  3.6.31 recall and use the quantitative relationship between current, charge and time.
  • 19. Factoids  The charge on one Electron is 1.60 x 10-19 C 0.000 000 000 000 000 000 160 Coulombs  There are roughly 1 x 1021 electrons in a 1 m length of metal wire ~1 000 000 000 000 000 000 000 electrons
  • 20. Current flow within a circuit  The flow of electricity in a circuit is due to the charge, Q, moving within the material (copper wires). The speed of the flow is known as the current (symbol I) This is similar to the flow of water in a river being called a current- when it flows fast there is a strong current.
  • 21. Current Definition How fast or the time it takes…  Electrical Current is the rate of flow of charge past a given point in a circuit The number of charged particles Current = Charge / Time Symbol Equation I =Q / t Units Equation Amps = Coulombs / Seconds
  • 22. Electrical Current  Reference Page 114
  • 23. Circuit Diagrams  Page 115  3.6.34 describe and record diagrammatically simple electric circuits. - Draw a circuit diagram of the circuit which is set up by Mr McClelland - A simpler way of representing a circuit visually is using the set of electrical circuit symbols to represent each component. (make sure you know them!)
  • 24. Draw the circuit Voltmeter in Switch parallel over a bulb Two Bulbs in parallel
  • 25. V A
  • 26. Conventional Flow v Electron Flow  Page 114- Electrical current is conventionally known as flowing from the positive terminal to the negative terminal.  However, we refer to the electrons as flowing from the negative to the positive due to the attraction that the negative charge has to the positive terminal.
  • 27. The Movement of Electrons  Conductors- The electrons are free to move within these materials, very little energy is required to free the electrons from their atoms. (Metals, carbon)  Insulators- Charge cannot move through these materials as they have very few free electrons. (Plastics, ceramics, rubber)
  • 28. Experiment- Electrical Current  Set up the following circuits and find the electrical current flowing at each point indicated. Parallel Series +
  • 29. Results  Table Point on the circuit Current (A) 0.25 0.25 0.5 0.25 0.25
  • 30. Conclusion  The ammeter measures the current flowing in the circuit as the electrons pass through it.  For a series circuit the electrical current will be the same at every point  For a parallel circuit the current entering the parallel section will be equal to the sum of the current of the branches of the parallel section (current splits)
  • 31. Extra Syllabus Reference-  3.6.36 recall that in a series circuit the current is the same everywhere.  3.6.38 recall that in a parallel circuit the sum of the currents in the branches is equal to the current entering the parallel section.
  • 32. So eh, what’s the current? Series- Parallel- + Current the same everywhere!! Current into the junction is equal to the current out
  • 33. Examples of current in a circuit  What is the reading on each of the following ammeters- A3 3A A1 A2
  • 34. Bad Parents…