b fields

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  • Created by: Anwen
  • Created on: 22-05-14 22:35
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  • B-fields
    • Magnetic field lines
      • always move N -> S
      • When two oppose there is a neutral point usually denoted by X
    • Flemming L.H.R
      • thumb=Motion First=Field second=Current
    • Flux Linkage = If the coil in the magnetic flux consists of N turns the flux linkage is given by N@ (@=thi) unit=WB(webber)
    • F=BIlsinO
      • Force on a straight wire carrying a current. If a current I flows in a length l of a wire at right angles to a magnetic field of flux density B(it's magnetic field strength)
        • F=BIl     B=F/Il
    • Flux density = the distance between two lines of the field (shorter distance greater density)
      • Equations used to calculate flux density
        • B=       (UoI)    ________   2(pie)a
    • Mgnetic Flux = BAsinO unit=webber D= if a single turn coil of wire encloses an area A and a magnetic Field B makes an angle O with the normal to the plane of the coil, the magnetic flux through the coil is given by @=ABcosO or  @=ABsinO
    • Relative permeability Ur = B/Bo usually from 1->300 for ferromagnetic material Ur is large and positive
    • The Ampere
      • To derive an expression for the force, two long straight parallel conductors at a distance 'a' apart in air carrying current I1 and I2 respectively as shown in the diagram -------->
        • B1=                  (Uo*I*1) _____________    2*(pie)*a
          • F=B1*I2*L
            • F=    Uo*I1*I2*l ______________ 2*(pie)*a
              • Wire 1 exerts a force on wire 2 and wire 2 exerts an equal and opposite force on wire 1
                • I1=I2=1A l=a=1m    subin F= Uo*I1*I2*l ___________ 2*(pie)*a
                  • Uo  =               4(pie)x10-7       Hm^-1
      • D= the ampere is that current which when flowing through 2 infinite thin wires one metre apart in vacuum produces a force between the wires of exactly 2x10-7N per m of length (A)
    • Force in a changing magnetic field
      • V=L/t
        • I=nq/t
          • t=L/v
            • I=nqv/L
              • F=BIL         =B{nq/L}*L =Bnqv singlecharge = F=Bqv Forelectrons = F=Bev
    • How to increase the field strength within a solenoid
      • filling the core with a ferrous metal e.g iron cobalt and nickel
        • B=UrUonI
        • The magnetic field outside the solenoid and the self inductance of the solenoid are increased in the same proportion.
    • Hall Voltage
      • DWhen a magnetic field B is applied to a conductor carrying current I at right angles to the field direction a so-called Hall volatage appears across the specimen at right angles to the B and I directions (L.H.R.)
      • Vh.prop.B  Vh=BI/nxq
        • B=magnetic field strength I=cuurent n=numberof charge carryers
          • Vh =Bvd d=distance between bottom and top.
      • The electrons move into the hall probe, and move in the opposite direction to thwe motion ~(LHR)~ when bottom layer is fullyaturated the electrons pass straight through the probe un deflected
    • Cyclotrons, Synchrotrons and Linear accelerators
      • Cyclotron
        • The charged particles are accelerated in a circular path where the magnetic field is constant. Whilst the radius of the curved path changes (in a swirly pattern) the particles are accelerated by applying a PD across the gap.
      • Synchrotrons
        • The charged particles are also accelerated in a circular path. However the radius of the path followed by the particle remains constant whilst the applied magnetic field changes.
          • Most of the worlds famous particle accelerators e.g CERN in switzerland use the synchrotron technique they reach about 99% the speed of light.
            • Advantages = It's possible to accelerate the particles to higher speeds. Higher energy means more energy and smaller waves and therefore the discovery of v. small particles e.g quarks
            • Disadvantages it's not possible to accelerate a continuous stream of particles. The particles are accelerated in small bunches then clear the machine before inserting the next bunch. (short burst of particles)
          • Advantages = It's possible to accelerate the particles to higher speeds. Higher energy means more energy and smaller waves and therefore the discovery of v. small particles e.g quarks
          • Disadvantages it's not possible to accelerate a continuous stream of particles. The particles are accelerated in small bunches then clear the machine before inserting the next bunch. (short burst of particles)
      • Linear accelerators
        • The future lies in the linear accelerators which accelerate particles in a straight line. The advantage being that they need less energy to operate because the particle don't expierience centripedal force / accleleration
    • Centrapedal Force +acceleration
      • F=            mv^2    __________ r
        • F=Bqv
          • F=ma
            • a=w^2r
              • v=rw
                • v^2=w^2r^2
                  • a=               v^2/r
                    • Bqv= mv^2/r
                      • Bq = mv/r
                        • for electrons Be=mv/r
    • Force between two wires carrying current
      • current in the same direction attract each other (pushed together by a stronger outer field)
      • If currents are in opposite direction then the wires repel each other (the strong central magnetic field pushes the wires apart)
    • Deflection of charged particles
      • Beta goes toward the positive in an electric field and alpha moves towards the negative(muchslower wvelocity than beta)
        • Ina magnetic field the alpha particle moves up

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