Charged particles in a magnetic field Flashcards Preview

A2 Physics F > Charged particles in a magnetic field > Flashcards

Flashcards in Charged particles in a magnetic field Deck (11):

What happens when a charged particle is moving in a magnetic field?

  • force is exerted
  • this is why a current-carrying wire experiences a force in a magnetic field
    • electric current is the flow of -vely charged electrons



Derive the equation F = BQv from F = BIL


use data sheet

  • electric current, I = Q / t
  • chargged particle which move a distance l in time t has a velocity, v = l / t
  • so l = vt
  • therefore  F = BIL = BQvt / t = BQv


Describe the deflection of a charged particle in a magnetic field?

  • deflected in a circular path




Why does the particle move with circular motion?

  • FLH rule says that the force n a moving charge in a magnetic field is always perpendicular ot its direction
  • mathematically, that is a condition for circular motion 




How do you use FLH rule for charged particles?

  • use your second finger (normally current) as the direction of motion for a positive charge
  • if particle carries a -ve charge, point second finger in opposite direction to its motion


why is force due to magnetic field independant of mass but the centripetal acceleration does?

  • F = BQv
    • no mass in equation
  • Newtons 2nd law
    • particles acceleration will be a = v2 / r
    • combining with newtons second law F = mv2 / r
      • this is force on a particle in circular orbit


Rearrange the equaiton to give r 

use data sheet

what happens if the raidus increases or decreases?

  • radius increase
    • particle deflected less
    • m or v increase
  • radius decreases
    • particle deflected more
    • B increase or Q increase


What are cyclotron?

  • make use of circular delflection
  • particle accelerators



What are the uses of cyclotrons?

  • medicine
  • radioactive tracers
  • high=energy beams of radioation for use in radiotherapy




What is a cyclotrons made up from~?>

  • two hollow semicircular electrode with a uniform magnetic field applied perpendicular to the plane of the electrons and an alternating potenttial difference between electrodes


How does a cyclotron work?

A image thumb