Charged particles in a magnetic field

Question 1

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

Answer 1

• 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

Question 2

Derive the equation F = BQv from F = BIL

use data sheet

Answer 2

• 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

Question 3

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

Answer 3

• deflected in a circular path

Question 4

Why does the particle move with circular motion?

Answer 4

• 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

Question 5

How do you use FLH rule for charged particles?

Answer 5

• 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

Question 6

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

Answer 6

• 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

Question 7

Rearrange the equaiton to give r

use data sheet

what happens if the raidus increases or decreases?

Answer 7

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

Question 8

What are cyclotron?

Answer 8

• make use of circular delflection
• particle accelerators

Question 9

What are the uses of cyclotrons?

Answer 9

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

Question 10

What is a cyclotrons made up from~?>

Answer 10

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

Question 11

How does a cyclotron work?

Answer 11