Physics, topic 7, electromagnetism

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  • electromagnetism
    • electromagnets and magnets
      • magnets
      • wires
        • charge going through a wire creates a magnetic field
        • solenoid: coil of wire
        • increase strength of solenoid by increasing coils, increasing current
      • electromagnet
        • put an iron bar in a solenoid
        • an be switched on and off
        • can be used in alarms
    • the motor effect
      • when a current in a wire is perpendicular to a magnetic field there is another perpendicular force.
      • F=BIL
        • F=force (newtons, N)
        • B=magnetic flux density (tesla, T)
        • I=current (amps, A)
        • L=length (metres, m)
      • uses
        • electric motors
          • an entire coil goes through a magnetic field
            • one side goes up, one goes down
              • the two ends of the wire alternate between split rings and keep it going
        • loud speakers
          • the magnet and wire do motor effect and the solenoid pushes outward
            • this moves the paper cone, creating vibrations and sound
    • generator effect
      • creating a PD in a wire which is moving in relation to a magnetic field
      • backwards motor effect
      • pass a magnet through a solenoid, to produce a PD
      • spin magnet in solenoid to produce AC
      • increase PD by increasing speed or strength of magnet
      • uses
        • generator
        • microphone
          • backwards speaker
          • set up speaker with no PD
            • sound waves push paper cone, causing magnet to move
              • creates PD, linked to speaker
    • transformers
      • step up transformer
        • increase PD
        • decrease current
        • more turns in secondary coil
      • step down transformer
        • decrease PD
        • increase current
        • more turns in primary coil
      • VsIs=VpIp
        • Is= secondary current
        • Untitled
      • Vp/Vs=Np/Ns
        • Np=turns in primary coil
        • Ns=turns in secondary coil
        • Vp= PD in primary coil
          • VsIs=VpIp
            • Is= secondary current
            • Untitled
        • Vs=PD in secondary coil


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