Physic Unit 3 Chapter 2

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  • Created on: 17-04-13 17:27
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  • Physics Unit 3 Chapter 3
    • Electromagnets
      • The force between two magnets:  like poles repel; unlike poles attract.
      • A magnetic field line is the line along which a plotting compass points.
      • An electromagnet consists of a coil of insulated wire wrapped round an iron core.
        • The magnetic field of the wire magnetises the iron bar strongly and when the current is switched off the iron loses most of its magnetism.
          • Iron easily loses it magnetism whereas steel is unsuitable because it keeps it magnetism when the current is switched off.
      • Electromagnets are used in scrapyard cranes, circuit breakers, electric bells and relays.
    • Untitled
      • The Motor Effect
        • In the motor effect, the force:
          • Is increased if the current or the strength of the magnetic field is increased.
          • It is right angles to the direction of the magnetic field and to the wire.
          • Is reversed if the direction of the current or the magnetic field is reversed.
        • An electric motor has a coil which turns when a current is passed through it.
        • Fleming's LH Rule
          • First finger - field. Second finger - Current. ThuMb - Movement.
    • Electromagnetic Induction
      • Electromagnetic induction is the process of creating a potential difference using a magnetic field.
      • When a conductor cuts the lines of a magnetic field, a potential difference is induced across the ends of the conductor.
      • When an electromagnet is used, it needs to be switched on or off to induce a pd.
    • Transformers
      • A transformer only works on ac because a changing magnetic field is necessary to induce ac in the secondary coil.
      • A transformer has an iron switch mode transformer which has a ferrite core.
      • A switch mode transformer is lighter and smaller than an ordinary transformer. It operates at high frequency.
      • A step up transformer must have more turns (coils) around the secondary coil than the primary coil.
    • Transformers in Action
      • Transformers are used to step potential differences up or down.
      • The transformer equation is primary pd/secondry pd.= number of primary turns/number of secondry turns.
      • For a step down transformer, the number of secondary turns is less than the number of primary turns and vice versa.
      • For a 100& efficient transformer, power supplied to the transformer = power delivered by the transformer which is primary current x voltage = secondary current x voltage.
      • The higher the grid pd, the greater the efficiency of transferring electrical power through the grid.
      • Pd = number of turns.
    • A Physics Case Study
      • We use physics in hospital whenever: -blood pressure (or temperature) is measured - an ECG recording is made - an endoscope is used - a scanner is used.
      • We measure blood pressure, ECG potential differences and exposure to ionising radiation in hospitals.
      • A CT scanner uses X-rays, which are ionising radiation and therefore can damage living tissue.
  • We use physics in hospital whenever: -blood pressure (or temperature) is measured - an ECG recording is made - an endoscope is used - a scanner is used.


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