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Volume B Chapter 18        Electricity
What we will Learn…• What is a current?• How to draw electric circuit diagrams• What is potential difference, voltage and ...
What is Electricity???               Definition:Electricity is a form of energy that canbe easily changed to other forms.
Where does Electricity come from?Mainly 2 sources:1) Power Stations   - Supply a lot of electricity   - Used in many elect...
How does an Electrical   Appliance Work?• To make an electrical appliance work,  electricity must flow through it.• The fl...
What is an Electric          Current???                electric                  cell            connecting               ...
Electric Charges• Electric charges are made up of positive  charges (protons) and negative charges  (electrons).• When the...
How does electricity flow?• The battery in a circuit gives energy to  the electrons and pushes them around  a circuit, fro...
How to Measure Current?• The SI unit for electric current is ampere (A).• Smaller currents are measured in  milliamperes (...
Instrument to Measure Current• An ammeter is an instrument used for  measuring electric current.
Ammeter• It must be connected in series in the circuit.• Positive side of ammeter must be connected  nearest to the positi...
Electric Circuits• Electric circuits are                   connecting wires  made up of electrical  components            ...
Electric Circuits • Incomplete circuits are called open circuits.                   connecting wire is             no sour...
An electric current flows       only when there is:• a source of electrical energy and• a closed circuit                  ...
How to draw Circuit Diagrams  Component            Symbol   Component           Symbol                          +         ...
Examples of circuit diagrams:
SwitchesA switch is used to open or close a circuit.                 Main switch used                 in buildingsSwitches...
Circuit diagrams for open   and closed circuitsOpen circuit.   Close circuit.Bulb does not   Bulb will lightlight up when ...
Series and ParallelThere are 2 ways in which an  electric circuit can be  arranged:1. Series2. Parallel
Series Circuit• A series circuit connects the components one  after the other• A single loop is formed• A break in any par...
Parallel Circuit• A parallel circuit divides into two or more branches.• The current divides and flows through each parall...
Which of the following is aseries circuit?Which is a parallel circuit? Series Circuit Parallel Cir
Draw the circuit diagram forthe following set up and statewhether it is a series orparallel circuit.
Draw the circuit diagram forthe following set up and statewhether it is a series orparallel circuit.
Which is brighter?
Which of the following is aseries circuit?Which is a parallel circuit? Series Circuit     Parallel Circ
Voltage• An electric cell gives energy to the electrons and  pushes them round a circuit. Voltage is a measure  of how muc...
How to Measure        Voltage?• The SI unit for voltage is volt  (V).• A voltmeter is an instrument  used for measuring vo...
Voltmeter• Voltmeters must be connected  in parallel to the circuit.• The positive side of voltmeter  is connected to the ...
Recall: Ammeter!!!• It must be connected in series in the  circuit.• Positive side of ammeter must be  connected nearest t...
Electromotive Force        (e.m.f)• Electromotive force is the  same as voltage.• E.m.f refers to the amount of  energy su...
Electromotive Force       (e.m.f)
Potential Difference       (P.d.)
Potential Difference•                      (p.d)    Remember Diffusion?• High  Low                                     el...
Resistance• When an electric current flows  through a circuit, there will be  some resistance that opposes it. (similar to...
Resistance• Good conductors of electricity  have LOW RESISTANCE. (Eg. Metal  objects)  – Electricity is able to flow    th...
Resistance• The SI unit for resistance is ohm ()• Different electrical components  have different resistance• For example...
Example 1• An electric rice cooker  operates at 240 V and uses a  current of 8 A. What is the  Voltage (V) of the rice coo...
Resistors• An electrical component that is specially made to have a  certain resistance is called a resistor.• They can be...
Fixed Resistors and        Variable Resistors• Fixed resistors have only one resistance value• Variable resistors can be a...
S/E: Resistors• Resistors can be connected in  series or parallel                                    extra resistor in    ...
S/E: Resistors in             Series• When resistors  are connected in  series, the  resistance will                      ...
S/E: Resistors in           Parallel• When resistors are  connected in parallel, the  resistance will decrease• This is be...
S/E: Resistors in            Parallel 1   1    1    1   =    +    + R   R1   R2   R3What is the                  6resista...
What we will Learn…• What is a current?• How to draw electric circuit  diagrams• What is potential difference, voltage  an...
Heating Effect of•         Electric Current    When an electric current flows through    a wire, the wire heats up. Electr...
A kettle uses both copper and nichrome wires.Copper has low resistance while nichrome has high resistance.Which material, ...
Heating Effect ofElectric Current   ARGON (inert/unreactive gas)    filament wire produces    heat and light  In a light b...
Chemical Effect of         Electric CurrentWhat is ELECTROLYSIS?Definition:• Electrolysis is the chemical change that occu...
ElectrolysisThere are 2 uses of  electrolysis:1) Electroplating2) Extraction of Metals
1. Electroplating• In electroplating, a key is  covered with a thin layer of  copper when electricity is                  ...
Uses of ElectroplatingMetal objects can beplated with athin layer of another
2. Extraction of metals• Some metals (eg. sodium, aluminium) are obtained  by electrolysis.• To extract the metal   – heat...
Magnetic Effect of a•               Current near a    A straight wire is placed    compass. When an electric current    fl...
Electromagnet• An electromagnet is a magnet that  is made by using electricity• It consist of a wire coiled around a  meta...
ElectromagnetThe magnetic effect of the electromagnet can be    increased by:1.   increasing the current (by using more ba...
Differences between anelectromagnet and a magnet:    Electromagnet            Magnet                      A permanent magn...
Uses of       Electromagnets•   Cranes that lift    iron/steel•   Iron/steel    separators                      crane•   E...
Electricity (ppt)
Electricity (ppt)
Electricity (ppt)
Electricity (ppt)
Electricity (ppt)
Electricity (ppt)
Electricity (ppt)
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Transcript of "Electricity (ppt)"

  1. 1. Volume B Chapter 18 Electricity
  2. 2. What we will Learn…• What is a current?• How to draw electric circuit diagrams• What is potential difference, voltage and E.M.F?• What is resistance?• S/E: Circuits arranged in series versus parallel• S/E: Fixed resistors versus variable resistors• Effects of electric current
  3. 3. What is Electricity??? Definition:Electricity is a form of energy that canbe easily changed to other forms.
  4. 4. Where does Electricity come from?Mainly 2 sources:1) Power Stations - Supply a lot of electricity - Used in many electrical appliances2) Electric Cells (batteries) - Supply a little electricity - Portable - Safe
  5. 5. How does an Electrical Appliance Work?• To make an electrical appliance work, electricity must flow through it.• The flow of electricity is called an electric current.• The path along which the electric current moves is called the electric circuit.
  6. 6. What is an Electric Current??? electric cell connecting wire filament flow of electronsDefinition:An electric current is the rate of flow of electriccharges in a circuit.
  7. 7. Electric Charges• Electric charges are made up of positive charges (protons) and negative charges (electrons).• When these charges flow in a circuit, a current is produced.
  8. 8. How does electricity flow?• The battery in a circuit gives energy to the electrons and pushes them around a circuit, from the negative terminal of the cell, round the circuit and back to the positive terminal of the cell.
  9. 9. How to Measure Current?• The SI unit for electric current is ampere (A).• Smaller currents are measured in milliamperes (mA). 1 A = 1,000 mA 1 mA = 0.001 A• Different electrical components and appliances require different sizes of current to turn them on.
  10. 10. Instrument to Measure Current• An ammeter is an instrument used for measuring electric current.
  11. 11. Ammeter• It must be connected in series in the circuit.• Positive side of ammeter must be connected nearest to the positive terminal of the battery (electric cell), and vice versa.
  12. 12. Electric Circuits• Electric circuits are connecting wires made up of electrical components electric cell• These components must be joined together without any gap in between to light bulb circuit board form a closed circuit. Note: Components refer to the light bulb, wires, battery
  13. 13. Electric Circuits • Incomplete circuits are called open circuits. connecting wire is no source of missing electrical energyBoth the circuits in the diagram are incomplete, hence they are knownas “open circuits”.
  14. 14. An electric current flows only when there is:• a source of electrical energy and• a closed circuit connecting wires electric cell light bulb circuit board
  15. 15. How to draw Circuit Diagrams Component Symbol Component Symbol + + An electric cell Battery Switch (open) Light bulb (lamp) Switch Switch (closed) Connecting wires Connecting wires (not joined) (joined)Symbols are used to represent the various electricalcomponents in circuits.
  16. 16. Examples of circuit diagrams:
  17. 17. SwitchesA switch is used to open or close a circuit. Main switch used in buildingsSwitches used on circuit
  18. 18. Circuit diagrams for open and closed circuitsOpen circuit. Close circuit.Bulb does not Bulb will lightlight up when up when thethe switch is switch is
  19. 19. Series and ParallelThere are 2 ways in which an electric circuit can be arranged:1. Series2. Parallel
  20. 20. Series Circuit• A series circuit connects the components one after the other• A single loop is formed• A break in any part of a series circuit stops the flow of current in the whole circuit.
  21. 21. Parallel Circuit• A parallel circuit divides into two or more branches.• The current divides and flows through each parallel branch.• If a component breaks or is removed, the other components remain on.
  22. 22. Which of the following is aseries circuit?Which is a parallel circuit? Series Circuit Parallel Cir
  23. 23. Draw the circuit diagram forthe following set up and statewhether it is a series orparallel circuit.
  24. 24. Draw the circuit diagram forthe following set up and statewhether it is a series orparallel circuit.
  25. 25. Which is brighter?
  26. 26. Which of the following is aseries circuit?Which is a parallel circuit? Series Circuit Parallel Circ
  27. 27. Voltage• An electric cell gives energy to the electrons and pushes them round a circuit. Voltage is a measure of how much energy the electrons receive.• Different voltages are supplied by different cells and batteries. 1.5 V Dry Cell 12 V Car Battery 9 V Dry Cell
  28. 28. How to Measure Voltage?• The SI unit for voltage is volt (V).• A voltmeter is an instrument used for measuring voltages.
  29. 29. Voltmeter• Voltmeters must be connected in parallel to the circuit.• The positive side of voltmeter is connected to the positive terminal of the cell, and vice versa.
  30. 30. Recall: Ammeter!!!• It must be connected in series in the circuit.• Positive side of ammeter must be connected nearest to the positive terminal of the battery (electric cell), and vice versa.
  31. 31. Electromotive Force (e.m.f)• Electromotive force is the same as voltage.• E.m.f refers to the amount of energy supplied by the electric source (eg. battery) to each unit of electric charge.
  32. 32. Electromotive Force (e.m.f)
  33. 33. Potential Difference (P.d.)
  34. 34. Potential Difference• (p.d) Remember Diffusion?• High  Low electric• Similarly, electric charges cell connecting wire will flow from a point of filament higher potential (energy) to lower potential flow of electrons•This difference in electric potential between 2 points in acircuit is known as the potential difference. It is the sameas VOLTAGE also.
  35. 35. Resistance• When an electric current flows through a circuit, there will be some resistance that opposes it. (similar to friction)• It can be measuredRbyResistance V = dividing R= voltage by the current. I V = Voltage I = Current
  36. 36. Resistance• Good conductors of electricity have LOW RESISTANCE. (Eg. Metal objects) – Electricity is able to flow through them very easily• Poor conductors of electricity have HIGH RESISTANCE. (Eg. Wood, cloth) – Electricity is not able to
  37. 37. Resistance• The SI unit for resistance is ohm ()• Different electrical components have different resistance• For example, nichrome wires have a higher resistance than copper wires. So should we use nichrome or copper to make wires?
  38. 38. Example 1• An electric rice cooker operates at 240 V and uses a current of 8 A. What is the Voltage (V) of the rice cooker? resistance 240 = 240 V R= 8 Current (I) = 30  =8A V R= I
  39. 39. Resistors• An electrical component that is specially made to have a certain resistance is called a resistor.• They can be connected in a circuit to resist the current flow.
  40. 40. Fixed Resistors and Variable Resistors• Fixed resistors have only one resistance value• Variable resistors can be adjusted to change the resistance. fixed resistor symbol variable resistor symbol •Variable resistors are useful in light dimmers and
  41. 41. S/E: Resistors• Resistors can be connected in series or parallel extra resistor in Resistors connected series results in dimmer bulb in SERIES extra resistor in Resistors connected parallel results in brighter bulb single resistor in PARALLEL
  42. 42. S/E: Resistors in Series• When resistors are connected in series, the resistance will 2 3 add up and increase.• R = RThe totalR3… 1 + R2 + resistance for this circuit is: 2+3=5
  43. 43. S/E: Resistors in Parallel• When resistors are connected in parallel, the resistance will decrease• This is because they will provide alternate routes for the current to flow.
  44. 44. S/E: Resistors in Parallel 1 1 1 1 = + + R R1 R2 R3What is the 6resistance of thecircuit? + 1 1 1 6 = R 6 6 1 = 2 = 1 R = 3 The final 6 R 3 resistance is
  45. 45. What we will Learn…• What is a current?• How to draw electric circuit diagrams• What is potential difference, voltage and E.M.F?• What is resistance?• S/E: Circuits arranged in series versus parallel
  46. 46. Heating Effect of• Electric Current When an electric current flows through a wire, the wire heats up. Electrical energy has been converted into heat energy.• The greater the resistance of the wire, the greater the amount of heat produced. This heating effect is used in common electrical appliances. Iron Kettle Hair Dryer
  47. 47. A kettle uses both copper and nichrome wires.Copper has low resistance while nichrome has high resistance.Which material, copper or nichrome, should be used for the heatingelement, and for the external wire? Use copper wire for the external wire as it has low resistance & produces less heat Use nichrome wire for the heating element as it has high resistance& produces a lot of heat
  48. 48. Heating Effect ofElectric Current ARGON (inert/unreactive gas) filament wire produces heat and light In a light bulb, the heated filament which is also a resistance wire, becomes so hot that light is also emitted.
  49. 49. Chemical Effect of Electric CurrentWhat is ELECTROLYSIS?Definition:• Electrolysis is the chemical change that occurs when an electric current passes through solutions or molten compounds.
  50. 50. ElectrolysisThere are 2 uses of electrolysis:1) Electroplating2) Extraction of Metals
  51. 51. 1. Electroplating• In electroplating, a key is covered with a thin layer of copper when electricity is - + passed through the solution. key copper copper on wire the key copper sulphate solution start after a few minutes
  52. 52. Uses of ElectroplatingMetal objects can beplated with athin layer of another
  53. 53. 2. Extraction of metals• Some metals (eg. sodium, aluminium) are obtained by electrolysis.• To extract the metal – heat the solid compound of the metal until it melts – pass an electric current through the molten compound
  54. 54. Magnetic Effect of a• Current near a A straight wire is placed compass. When an electric current flows through the wire, the compass needle is deflected. This shows that an electric current has a magnetic effect. current in wire compass needle is deflected
  55. 55. Electromagnet• An electromagnet is a magnet that is made by using electricity• It consist of a wire coiled around a metal rod (eg. of wire coil Iron) iron core to battery compass needle is strongly attracted to iron core
  56. 56. ElectromagnetThe magnetic effect of the electromagnet can be increased by:1. increasing the current (by using more batteries)2. increasing the number of turns of wire in the coil3. Using an iron rod
  57. 57. Differences between anelectromagnet and a magnet: Electromagnet Magnet A permanent magnetA temporary magnet which retainswhich can be turned magnetism until it is on and off using purposely electric current. demagnetised (spoilt).Magnet can be made Magnet remains thestronger or weaker same strength
  58. 58. Uses of Electromagnets• Cranes that lift iron/steel• Iron/steel separators crane• Electric bells• Magnetically levitated trains• Electric motors Electric bell Electric motor in fans
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