TAP 519- 2: Measuring the momentum of moving charged
particles
Analysing the motion of a charged particle in a magnetic field can lead to a determination of
its momentum.
Measuring the momentum of moving charged particles
velocity v





force F


circular path,
radius r

magnetic field B
into screen








charge q
velocity v
motion in circle
magnetic force
m v2
= force F
r
force F = qvB
m v2
= qvB
r
p = mv = qrB
at relativistic speed
p = qrB
is still true but
p > mv
Momentum of particle proportional to radius of curvature of path
Practical advice
This diagram is here so that you can discuss it with your class.
External reference
This activity is taken from Advancing Physics chapter 16, 140O