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Flashcards

Magnetism

Jio Jenassi Physics A-Level Inglês 55 flashcards

Magnetism

Flashcards do conjunto (55)

  1. 1What is electromagnetic induction?•Relative motion between a conductor and a magnetic field causes the magnetic flux to change.
    •The change in magnetic flux causes an emf to be induced across the conductor.
  2. 2In electromagnetic induction, what will occur two ends of the conductor are joined by a connecting wire?•An induced current will flow
  3. 3What are the two laws of electromagnetic induction?•Lenz's law and Faraday's Law
  4. 4What is Lenz's law of electromagnetic induction?•The direction of the induced emf is such as to oppose the change causing it.
  5. 5What is another name given to Lenz's law?•The law of Cussedness.
  6. 6What is Faraday's law of Electromagnetic induction?•The magnitude of the induced emf (current) is directly proportional to the rate of change of magnetic flux.
  7. 7How can the direction of the induced emf be reversed?•Reversing the moving direction
    •Reversing the polarity of the magnetic field.
  8. 8What is the Faraday - Lenz law of electromagnetic induction?What is the Faraday - Lenz law of electromagnetic induction?
  9. 9What occurs when a straight conductor moves through a magnetic field?•When a straight conductor moves through a magnetic field, the flux is cut.
    •The flux changes.
    •So an induced emf is across the conductor by electromagnetic induction.
  10. 10What can be said about the charges on the ends of the conductor when the emf is induced?•One side becomes positive
    •The other side becomes negative.
    •When two ends are connected by a conducting wire, an induced current will flow.
  11. 11Why is there a force on a moving conductor with induced current in a magnetic field?•The induced current creates a magnetic field for the conductor.
    •Motor effect occurs
  12. 12What occurs to the free or mobile electrons in the conductor?•The free or mobile electrons in the conductor move in the same direction as the moving direction.
    •The direction of this current is opposite to that of the electrons.
  13. 13What is the special name given to this type of current?•Virtual current
    •Virtual current cant be measured.
  14. 14Why is that one end becomes negatively charged and the other end is positively charged?•When the conductor moves through the magnetic field, a resultant force is exerted on the electrons.
    •The resultant force causes the electrons to move to one end, making it negative.
  15. 15How can the direction of the induced emf be found?•Using Fleming's right hand rule.
  16. 16What is Fleming's right hand rule?•Thumb, index and middle fingers of the right hand are kept mutually perpendicular.
  17. 17What does the thumb, index and middle finger represent?•Thumb - Resultant force
    •First finger - direction of magnetic field
    •Second finger - Direction of current
  18. 18What happens when a magnet moves towards a solenoid?•When a magnet moves towards a solenoid or moves away, the flux passing through the solenoid changes.
    •This causes a emf to be induced on the conductor.
  19. 19What are the applications of Electromagnetic induction?•Bicycle dynamo
    •AC generator (Alternator)
    •Transformer
  20. 20How does a bicycle dynamo work?•When a bicycle wheel rotates, the axel in the dynamo rotates.
    •The rotation causes the magnet to rotate.
    •The magnetic flux passing through the coil changes.
  21. 21What happens in the bicycle dynamo when the flux changes?•An emf is induced at the ends of the coil.
    •When the ends of the coil are connected to the bulb, the current induced in the circuit will cause the bulb to light up.
  22. 22What type of current is induced in a bicycle dynamo?•Direct current.
  23. 23How does an AC generator or Alternator work?•Mechanical energy is used input to turn the coil in the magnetic field.
    •When the axel rotates, the coil rotates and the cuts the magnetic flux.
    •This cutting causes an emf to be induced across the coil.
  24. 24How is alternating current made using an AC generator?•After half a revolution, the polarity of the induced emf will change.
    •Therefore, the direction of current will change, giving rise to AC.
  25. 25How can the strength of the induced emf increase?•Rotate the turbine or axel faster.
    •Increase the strength of the magnets.
    •Increase the number of turns in the coil.
  26. 26How can the strength of the magnets increase?•By replacing the current magnets with stronger magnets.
    •By keeping the magnets closer together.
  27. 27What is a transformer?•A device which can either increase or decrease an alternating voltage.
  28. 28What are the 2 types of transformers?•A step up transformer - increases the voltage.
    •A step down transformer - decreases the voltage.
  29. 29What is the significance of the secondary coil with respect to the primary coil in both types of transformers?•Step up - Secondary coil has more turns.
    •Step down - Secondary coil has less turns.
  30. 30Which coil is the AC Power supply connected to?•The Primary coil
  31. 31What is the importance of the soft iron core within the transformer?•The core carries the whole magnetic flux through the secondary coil.
    •Consequently, there is a strong magnetic flux linkage through the secondary coil.
  32. 32What is the importance the alternating current in a transformer?•A magnetic field is induced in a current carrying wire.
    •When the direction of current changes, the magnetic field changes.
    •When the magnetic field changes, an emf is induced across the secondary coil.
  33. 33In terms of magnetic flux, how does a Step up transformer increase the magnitude od the induced emf?•Due to the greater number of turns in a secondary coil than a primary coil, the rate of change of magnetic flux linkage is greater.
    •Therefore, the induced emf is greater than the supply voltage.
  34. 34In terms of magnetic flux, how does a Step down transformer decrease the magnitude of the induced emf?In a step down transformer, the secondary coil has less turns compared to the primary coil.
    The rate of change of magnetic flux will be smaller.
    Hence, the induced emf will be smaller than the supply voltage.
  35. 35What will occur if a DC supply is used instead of an AC supply?•A magnetic field is induced across the wires in fraction of a second.
    •The flux linkage through the secondary coil changes as the magnetic flux density increases from zero to a steady value.
    •An emf is induced in the secondary coil for a fraction of a second.
  36. 36What are the applications of transformers?•Step down - mobile phone chargers, laptop charges.
    •Both step up and step down are used in the national grid.
  37. 37Where are step down and step up transformers used within the national grid?•Step up - Beginning of transmission.
    (near power station)
    •Step down - end of transmission line.
    (near our Houses)
  38. 38Why is electricity sent as a high voltage rather than a high current?If electricity is sent as high current:
    •Large amount of electrical energy is wasted as heat energy.
    •Thick wires should be used to withstand the high temperatures.
    •Hence, there is increased costs.
  39. 39What are 3 groups in which substances can be divided into based on magnetism?•Magnets
    •Magnetic materials
    •Non magnetic materials.
  40. 40What is a Magnet?•A substance which has its own magnetic field.
    •It can either attract or repel other magnetic poles or magnetic materials.
  41. 41What is a magnetic material?•A substance which does not have its magnetic field.
    •However, when placed next to a magnet, a magnetic field is induced around the magnetic material.
  42. 42What are the two groups which Magnetic materials can be divided into?•Soft Magnetic materials
    •Hard magnetic materials
  43. 43What is the difference soft magnetic materials and hard magnetic materials?•Soft - Temporary magnetic field (easy to magnetize). Ex: Iron
    •Hard - Permanent magnetic field (difficult to magnetize). Ex: Steel
  44. 44What are non magnetic materials?•Materials which do not have their own magnetic field or cant have an induced magnetic field.
  45. 45What are Magnetic poles?•The points where the magnetic field strength is maximum compared to other parts of the magnet.
  46. 46What is a Magnetic field?•The region in the space where the magnetic force acts upon a magnetic material or magnetic pole.
  47. 47What is a Magnetic field line?•A magnetic field shows the direction of the magnetic force.
  48. 48What are the properties of the magnetic field lines?•Directed from north to south
    •They never intersect.
    •There are no loose ends.
    •If the magnetic field is uniform, field lines are equally spaced and parallel.
  49. 49What can be deduced from the magnetic field if the field lines are close together?•The magnetic field is strong.
  50. 50What can be said the magnetic field within a neutral point?•The fields are in the opposite direction.
    •Therefore, the magnetic fields cancel each other out.
    •Therefore, there is no resultant magnetic field or force.
  51. 51What are the two methods in which magnetic field patterns can be investigated?•Iron fillings method.
    •Plotting compass method.
  52. 52What can be said about Earth's Magnetic field?•Geographical north - South pole
    •Geographical south - North pole
  53. 53Why are horizontal and vertical components of the Earth's magnetic field considered?•The Earth's magnetic field is at an angle.
  54. 54What are the applications of electromagnetism?•Relay switch
    •Electric bell
    •Circuit breaker
  55. 55How does electromagnetism work in a relay

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A-Level Physics FlashCards sobre Magnetism, criado por Jio Jenassi em 20-02-2016.
Criado por
Jio Jenassi
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