Spinning Around Again
Forces on Charges
Here we are again:Today we will have a discussion about charge
motion in magnetic fields and so some observations of wires in magnetic fields.
There is A new WebAssign (Aren’t you excited??) posted.
I am still working on the gradebook so you can see your grades all together.
Friday will be a Quiz on this week’s work. Maybe last week’s too!
Next week more of the same.
Last Session:F=Bqv Sin(B,V)Right hand rule for direction.
A LONG, STRAIGHT WIRE
rIB o
2
AmT104 7 o
permeability of free space
VECTOR!
Current OUT of Paper
450
1 Ampere
1 MeterX
What is magnetic field at X??
rIB o
2
7
7
(4 10 T m A) (1 )2 (1 )
2 10
AmpBmeter
B T
DIRECTION? “NW”
B
REMEMBER:The effect of the sign of a moving
Positive and negative charges will feel opposite effects from a magnetic field.
The Velocity Selector
Magnetism7
Magnetism8
Let’s Look at the effect of crossedcrossed E and B Fields:
xx xx
xx
•q , m
B
v
E
Magnetism9
What is the relation between the intensities of the electric and magnetic fields for the particle to move in a straight line ?.
•FEFB
FE = q E and FB = q v B
If FE = FB the particle will movefollowing a straight line trajectory
q E = q v B
v = E / B
xx xx
xx
•q m
B
v
EB
E
A charged particle is injected into a Magnetic Field.Can the field do WORK on the particle?
A YESB NOC It depends on the direction
the particle is moving inwith respect to the field.
D I want to go back on SpringBreak!
The Motion of a Charged Particle in a Magnetic Field
The electrical force can do work on acharged particle.
The magnetic force cannot do work on acharged particle.
Parabola
The Motion of a Charged Particle in a Magnetic Field
The magnetic force always remainsperpendicular to the velocity and is directed toward the center of the circular path.
rvmFc
2
rvmqvB
2
qBmvr
21.4 The Mass Spectrometer
eBmv
qBmvr
212
212
mv qV
mv eV
magnitude ofelectron charge
KE=PE
22
2B
Verm
Mass Spectrometer
Magnetism14
Smaller Mass
Kratos Profile HV-3 Gas Chromatograph & Direct Probe Mass SpectrometerDescriptionMedium resolution double focusing (E/B) magnetic sector mass spectrometer with gas chromatograph and direct probe inlets; electron impact and chemical ionization sources.
Magnetism17
Figure 3.5.1 Chromatogram at target concentration. 1 = benzalazine, 2
AcPP.
EXAMPLLE: Molecular structure and mass spectrum of 1-acetyl-4-(2-pyridyl)piperazine. The mass spectrum was obtained with a Perkin-Elmer ion trap detector.
An Example
Magnetism20
A beam of electrons whose kinetic energy is K emerges from a thin-foil “window” at the end of an accelerator tube. There is a metal plate a distance d from this window and perpendicular to the direction of the emerging beam. Show that we can prevent the beam from hitting the plate if we apply a uniform magnetic field B such that
22
2demKB
Problem Continued
Magnetism21
r
22
22
2
e2mKB
:Bfor Solvee22
eBm
2 so 21
qBmvr
Before From
d
dBmK
mKr
mKvmvK