Using Magnetic Fields to Keep Things Moving

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  • Using Magnetic Fields to Keep Things Moving
    • Electromagnets
      • The forces 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.
      • Electromagnets are used in scrapyard cranes, circuit breakers, electric bells, and relays.
    • The Motor Effect
      • In the motor effect, the force:
        • is increased if the current of the strength of the magnetic field is increased.
        • is at 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.
    • Electromagnetic Induction
      • When an electromagnet is used, it needs to be switched on or off to induce a pd.
      • Electromagnetic induction is the process of creating a pd, using a magnetic field.
      • When a conductor cuts the lines of a magnetic field, a pd is induced across the ends of the conductor.
    • Transformers
      • A transformer has an iron core, unless it is a switch mode transformer, which has a ferrite core.
      • A transformer only works on AC because a changing magnetic field is necessary to induce AC in the secondary coil.
      • A switch mode transformer is lighter and smaller than an ordinary transformer.It operates at high frequency.
    • Transformers in Action
      • Transformers are used to step pd up or down.
      • For a step-down transformer, n(s) is less than n(p). For a step-up transformer, n(s) is greater than n(p).
      • The transformer equation is: V(p)/V(s) = n(p)/n(s)
        • V(p) is the primary pd
        • V(s) is the secondary pd
        • n(p) is the number of primary turns
        • n(s) is the number of secondary turns
      • For a 100% efficient transformer, V(p) x I(p) = V(s) x I(s)
        • I(p) is the current in the primary coil
        • I(s) is the  current in the secondary coil
    • A Physics Case Study
      • We measures blood pressure, ECG potential differences, and exposure to ionising radiation in hospitals.
      • We use physics in hospitals whenever:
        • blood pressure (or temperature) is measured.
        • an ECG recording is made.
        • an endoscope is used.
        • a scanner is used.
      • Untitled
  • Transformers
    • A transformer has an iron core, unless it is a switch mode transformer, which has a ferrite core.
    • A transformer only works on AC because a changing magnetic field is necessary to induce AC in the secondary coil.
    • A switch mode transformer is lighter and smaller than an ordinary transformer.It operates at high frequency.

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