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Bill and Bev
Force on a Moving Charge
The force on a charge q, is
F = Bqv
where v is the velocity
B
q
F
v
Link to Circular Paths
The force causes the particle to travel in a circular path
Link to Circular Paths
F = Bqv
F=
2
mv
r
Bqv =
2
mv
r
r = mv
Bq
The radius of curvature depends on the strength of the
field, the mass of the particle, the charge of the
particle and the velocity.
Mass Spectrometer
Link to Circular Paths
T = 2pir
v
r = mv
Bq
T = 2 pi m
BQ
Questions
-31
A particle of mass 9.1 x 10 kg and with a charge of
1.6 x 10-19 C, is moving at 4.5 x 106 ms-1. It enters a
uniform magnetic field of flux density 0.15 mT at 90
degrees. What is the radius of its circular path.
Magnetic Flux
The magnetic flux density (B) x the area swept out (A)
= magnetic flux (theta)
Units Webber
Electromagnetic
Induction
A moving charge in a
magnetic field
experiences a force
Therefore moving a conductor in a
(to make it move).
field will cause a current to flow.
This is electromagnetic induction.
Or a varying magnetic field over a
conductor will also cause a current.
Electromagnetic Induction
Flux cutting.
The conductor has
to cut field lines for
an emf to be
induced.
Magnetic Flux Linkage
Through a coil of N turns
n theta = n BA
when the magnetic field is along the normal
(perpendicular) of the coil face the N theapta = NBA
- When the coil is turned 180 then N theta = -NBA
- When the magnetic field is parallel to the coil flux
linkage = 0
-
Faraday's Law
The induced emf in a conductor
is equal to the rate of change of
flux linkage through the circuit.
1. Write this out as an equation.
2. Derive the equation from V= W/Q