Transcript Last four slide sets

10.1
Average=73
Average = 64
Which one of the following statements concerning permanent
magnets is false?
A) The north pole of a permanent magnet is attracted to a south
pole.
B) All permanent magnets are surrounded by a magnetic field.
C) The direction of a magnetic field is indicated by the north pole
of a compass.
D) Magnetic field lines outside a permanent magnet originate from
the north pole and end on the south pole.
E) When a permanent magnet is cut in half, one piece will be a
north pole and one piece will be a south pole.
Which one of the following statements concerning the magnetic
force on a charged particle in a magnetic field is true?
A) The magnetic force is a maximum if the particle is stationary.
B) The magnetic force is zero if the particle moves perpendicular
to the field.
C) The magnetic force is a maximum if the particle moves parallel
to the field.
D) The magnetic force acts in the direction of motion for a
positively charged particle.
E) The magnetic force depends on the component of the particle's
velocity that is perpendicular to the field.
Which one of the following statements best explains why a constant
magnetic field can do no work on a moving charged particle?
A) The magnetic field is conservative.
B) The magnetic force is a velocity dependent force.
C) The magnetic field is a vector and work is a scalar quantity.
D) The magnetic force is always perpendicular to the velocity of the
particle.
E) The electric field associated with the particle cancels the effect of
the magnetic field on the particle.
A charged particle enters a uniform magnetic field and
follows the circular path shown in the drawing.
The charge on the particle is:
A Positive
B Negative
C Neutral
D North
E South
Magnetism
8
RECALL
v2
Centripeta l Accelerati on 
r
mv 2
Centripeta l Force 
r
The magnetic force is qvB
mv 2
qvB 
r
mv
r
Bq
Recall : v  r or r  v/ 
v Bq

r m
This is called the cyclotron

angular frequency
Magnetism
9
Bq

  2f
m
mv T  period 
r
Bq
Magnetism
1
f
10
PITCH
P  v parallelT
P
Magnetism
11
Force on a Wire
Plates are optional
but you should try
them.
*More Magnetism
10.2
Detector Array
mv 2
 qvB
r
mv
 charge 
r

ratio

Bq
 mass 
FE  qE
qE  qvB
FB  Bqv
E
v
B
An electrical current is flowing out of the
page. Looking INTO the current, the
magnetic field is
A
B
C
Clockwise
Zero
Counterclockwise
A current carrying conductor is oriented as shown in the diagram.
The FORCE on the wire with respect to the diagram is:
A
B
C
D
E
Left
Right
In
Out
Up or Down
N
I
S
A current carrying conductor is oriented as shown in the diagram.
The FORCE on the wire with respect to the diagram is:
A
B
C
D
E
Left
Right
In
Out
Up or Down
N
I
S
v
B
Two parallel wires have electric currents that are
flowing in the same direction. The two wires will
A
B
C
Attract
Repel
Have no interaction
F  Bil
You will derive this in the unit.
Magnetism
• Placed over a compass,
the wire would cause the
compass needle to deflect.
This was the classic
demonstration done by
Oersted as he
demonstrated the effect.
22
0 I
B
2r
r
Tm
 0  4 10
(exact)
A
7
The permeability constant (μ0), also known as the magnetic constant or
the permeability of free space, is a measure of the amount of resistance
encountered when forming a magnetic field in a classical vacuum. The
magnetic constant has the exact (defined) value µ0 = 4π×10−7 ≈
1.2566370614...×10−6 H·m−1 or N·A−2).
Magnetism
23
Magnetism
First wire produces a magnetic field at the
second wire position.
The second wire therefore feels a force = Bil
24
B From First Wire
 0 I1
B
2r
 0 I1
F  BI 2l 
I 2l
2r
F  0 I1 I 2

l
2r
Magnetism
25
Plates are optional
but you should try
them.
How about a QUIZ???
L-10.3
c
0 I
I 
B
c 
2 r
r 
I3
a 2
2
r=a
1
c
c
I
a
I
a
Current
out
c(2)
I 2
I 2
2
2I
c

c
a 2
a
2
a 2
I3  2I
Klicquer Question
PHYSICS
Points A, B and C form an equilateral
triangle. Two parallel wires at B and C carry
equal currents into the page. As a result
of these two currents, what is the DIRECTION
of the magnetic field at point A?
A
B
C
D
E
To the right
To the Left
Down
Up
In or out of the plane of ABC

x
B
A
x
C
Discussion
PHYSICS

A
A - Right
x
B
x
C
Kratos Profile HV-3 Gas Chromatograph & Direct Probe Mass
Spectrometer
Description
Medium resolution double focusing (E/B) magnetic sector mass spectrometer with gas chromatograph and direct
probe inlets; electron impact and chemical ionization sources.
EXAMPLE: Molecular structure and mass spectrum
of 1-acetyl-4-(2-pyridyl)piperazine. The mass
spectrum was obtained with a Perkin-Elmer ion trap
detector.
Consider a section of wire.
In time t, a charge Q
passes through the wire.
F=Bqv=BQv
In time t, a charge I t passes
through the first surface.
I=
Q
; So Q=It
t
Force
Q
F  BQv  B
tv  BIL
t
Current Loops in Magnetic Fie
What is force
on the ends??
Loop will tend to rotate due to the torque the field applies to the loop.
Magnetism
39
OBSERVATION
Force on Side 2 is out
of the paper and that on
the opposite side is into
the paper. No net force
tending to rotate the loop
due to either of these forces.
The net force on the loop is
also zero,
pivot
Magnetism
40
t1=F1 (b/2)Sin(q)
=(B i a) x
(b/2)Sin(q)
total torque on
the loop is: 2t1
Total torque:
t=(iaB) bSin(q)
=iABSin(q)
(A=Area)
Magnetism
41
t=N(iaB) bSin(q)
=NiABSin(q)
DEFINE Magnetic Moment :
  NiA
t   B sin(q )
This is a very sensitive instrument and is easily damaged.
If the conductor is a loop, the torque can
create an electric motor.

Last Unit:
The Old and the New
Magnetism 11.1
1
We will complete the chapter
2
We will look at Evil Lentz
3
We will complete the current and the next
unit!
4
There will be a Friday Quiz
Transition
s
BN
 I
B 0
2 r
0 I
2R
B  Huh ??
Company Logo
www.themegallery.com
The Magnetic Field in a Coil
S
N
Yikes … it’s a magnet!!!
A.
B.
C.
D.
The field inside the coil is just
N times the field from a single
coil.
The field obtained by adding
the fields from each coil
separately. Don’t know how,
though.
The field cannot be calculated
with the tools we currently
have.
The field is just another way
to reduce our grades!!
Ampere to the Rescue! (1775-1836)
Notice
Ampere’s Law
 Bs  Bl   NI
B=0
0
B  s
Bl  0 NI
N
B  0 I  0 nI
l
l
Gauss 1777-1955



The movement of
the magnet closer
to the coil
increases the
“amount of
magnetic field”
going through the
coil.
This causes a
current to develop
in the coil.
This process is
called INDUCTION.

GENERAL EXPRESSION FOR MAGNETIC FLUX
  BA cos 
  BA cos 
  BA
0
GRAPHICAL INTERPRETATION OF MAGNETIC FLUX
The magnetic flux is proportional
to the number of field lines that pass
through a surface.
Induction
4/1/2016
64
   Bi cos(i )Ai
i
Add up all of these pieces
that are INSIDE the loop.
65
66
When you change the flux through a conducting loop, the
CURRENT induced into the loop by this change will
flow in such a way to create a flux change that opposes
the changing flux that is causing the current in the first pla
   Bi cos(i )Ai
i

Change any or all of the
◦
◦
◦
◦
◦

Bi
Ai
i
Change the SHAPE of the loop
Change the ANGLE that the loop makes
with the magnetic field (subset of
above)
And the Flux will change!
68
EXAMPLE OF NASTY LENZ
+ Handout
Don’t calculate the current … just the direction of the
current and explain to the class!