Magnetism

• When a magnetic field is perpendicular to a current-carrying wire, does the wire feel a force?

  Yes

  F=BIL
• Fleming's left hand rule

  Thumb - Force

  First Finger - Field

  Second Finger - Current
• Magnetic Flux Density (B)

  Flux density measured in Tesla (T) or Weber/meters^2 (Wbm^-2), is the flux per metre squared
• When does a charged particle moving through a field feel a force?

  When it is travelling Perpendicular to the field lines
• Force on a moving charge

  F=BQv
• Is the force applied to the particles applied perpendicular to the particles motion or in one direction?

  Perpendicular to its motion, causing it to movie in a circular motion.
• Which fields do cyclotrons use?

  Electric and Magnetic Fields
• How does a Cyclotron work and what is the purpose of the fields?

  • A cyclotron is made up of 2 Dees with a magnetic field applied perpendicular to the Dees and an AC current applied between them
  • Each Dee is a metal electrodes with opposite charges, this creates an electric field in the gap between the two Dees, which accelerates the particles
  • The magnetic field causes the particles to move in a circular motion, which allows it to gain speed while minimising space. As they speed up the radius of their motion increases, until it breaks free tangential to one of the Dees
• Magnetic Flux

  $\phi=$$BA$

  Flux = Flux Density x Area
• Flux Linkage


  $N\phi$ = The number of turns cutting the flux at one time
• Flux Linkage of a coil rotating through a magnetic field

  $N\phi=$$BAN\cos\theta$
• Faraday's Law

  The induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage
• Lenz's Law

  The direction of the induced e.m.f. is such as to oppose the change that induces it
• Lenz's Law equation

  $\epsilon=$$-N\frac{\Delta\phi}{\Delta t}$
• What happens when you move a straight conductor through a magnetic field?

  The electrons experience a force pushing them to one end of the conductor creating an e.m.f across the conductor. The rod obeys Faraday's law, it is changing flux as it moves through the field hence an e.m.f is induced
• EMF produced when rotating a coil at a constant rate in a magnetic field

  $\epsilon=$$BAN\omega\sin\left(\omega t\right)$
• When a magnetic field is perpendicular to a current-carrying wire, does the wire feel a force?

  Yes, it feels a force.
• What is the equation for the magnitude of the force on a current-carrying wire in a magnetic field?

  F = BIl
• What does 'l' represent in the equation F = BIl?

  Length of the wire
• What does 'B' represent in the equation F = BIl?

  Magnetic flux density
• What does 'I' represent in the equation F = BIl?

  Current in the wire
• What does Fleming's left hand rule represent?

  It represents force, field, and current.
• What does the thumb represent in Fleming's left hand rule?

  Thrust/Force
• What does the first finger represent in Fleming's left hand rule?

  Field (Magnetic)
• What does the second finger represent in Fleming's left hand rule?

  Current
• What is magnetic flux density (B)?

  Flux density measured in Tesla (T).
• How is magnetic flux density defined?

  It is the flux per meter squared.
• When does a charged particle feel a force in a magnetic field?

  When it is perpendicular to the field.
• What is the equation for the force felt by a moving charge in a magnetic field?

  F = BQv
• How is the force applied to particles in a magnetic field?

  Perpendicular to its motion.
• What motion does the force cause a charged particle to undergo?

  Circular motion.
• Which fields do cyclotrons use?

  Electric and magnetic fields.
• What is the purpose of the electric field in a cyclotron?

  To accelerate the particles.
• What is the purpose of the magnetic field in a cyclotron?

  To cause circular motion of particles.
• How does a cyclotron work?

  Particles move in circular paths, gaining speed.
• What is the equation for magnetic flux?

  Φ = BA
• What does Φ represent in the equation Φ = BA?

  Magnetic flux.
• What is flux linkage?

  NΦ = number of turns cutting the flux.
• What is the flux linkage of a rectangular coil rotating through a magnetic field?

  NΦ = BANcosΘ
• What is Faraday's Law?

  Induced e.m.f. is proportional to rate of change of flux.