10.1 average = 64 average=73 which one of the following statements concerning permanent magnets is...

10.1

Average = 64

Average=73

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 PositiveB NegativeC NeutralD NorthE South

Magnetism 8

Magnetism 9frequencyangular

cyclotron thecalled is This

v/ror r v:Recall

r

mv qvB

qvB is force magnetic Ther

mv Force lCentripeta

r

v on Accelerati lCentripeta

RECALL

2

2

2

m

Bq

r

v

Bq

mvr

Magnetism 10

Bq

mvr

m

Bq

fperiodT

f

1

2

Magnetism 11

TvP

PITCH

parallel

P

Force on a Wire

Plates are optionalbut you should trythem.

*More Magnetism

10.2

Detector Array

E

B

F qE

F Bqv

qE qvB

Ev

B

2

charge ratio

mass

mvqvB

r

mvr

Bq

An electrical current is flowing out of the page. Looking INTO the current, the magnetic field is

A ClockwiseB ZeroC Counterclockwise

A current carrying conductor is oriented as shown in the diagram.The FORCE on the wire with respect to the diagram is:

A LeftB RightC InD OutE Up or Down

IN S

A current carrying conductor is oriented as shown in the diagram.The FORCE on the wire with respect to the diagram is:

A LeftB RightC InD OutE Up or Down

IN S

B

v

Two parallel wires have electric currents that areflowing in the same direction. The two wires will

A AttractB RepelC Have no interaction

You will derive this in the unit.

F Bil

Mag

netism

22

• 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.

Magnetism 23

r(exact) 104

2

70

0

A

Tm

r

IB

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).

Mag

netism

24

First wire produces a magnetic field at the second wire position.

The second wire therefore feels a force = Bil

Magnetism 25

r

II

l

F

lIr

IlBIF

r

I

2

2

2B

First Wire From B

210

210

2

10

Plates are optionalbut you should trythem.

How about a QUIZ???

L-10.3

0

2

I IB c

r r

2

1

Ic

a

Ic

a

2 2 2 2(2)

2 2 2

I I Ic c c

a a a

r=a

Current out

3

2

Ic

a

3 2I I

PHYSICS

x x

A

CB

Points A, B and C form an equilateraltriangle. Two parallel wires at B and C carryequal currents into the page. As a resultof these two currents, what is the DIRECTIONof the magnetic field at point A?

A To the rightB To the LeftC DownD UpE In or out of the plane of ABC

Klicquer Question

PHYSICS

x x

A

CB

Discussion

A - Right

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.

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= ; So Q=I tQ

t

Force

QF B Qv B tv BIL

t

Current Loops in Magnetic FieldsCurrent Loops in Magnetic Fields

Magnetism 39

Loop will tend to rotate due to the torque the field applies to the loop.

What is forceon the ends??

Magnetism 40

pivot

OBSERVATION

Force on Side 2 is outof the paper and that onthe opposite side is into the paper. No net forcetending to rotate the loopdue to either of these forces.

The net force on the loop is also zero,

Magnetism 41

1=F1 (b/2)Sin() =(B i a) x (b/2)Sin()

total torque on the loop is: 21

Total torque:

=(iaB) bSin() =iABSin()

(A=Area)

=N(iaB) bSin() =NiABSin(

sin( )

NiA

B

DEFINE Magnetic Moment

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:

Magnetism 11.1The Old and the New

We will complete the chapter

1

We will look at Evil Lentz2

We will complete the current and the next unit!

3

There will be a Friday Quiz4

Transitions

0

2

IB

r

0

2

IB N

R

www.themegallery.comCompany Logo

??HuhB

The Magnetic Field in a Coil

NS

Yikes … it’s a magnet!!!

A. The field inside the coil is just N times the field from a single coil.

B. The field obtained by adding the fields from each coil separately. Don’t know how, though.

C. The field cannot be calculated with the tools we currently have.

D. The field is just another way to reduce our grades!!

Ampere to the Rescue! (1775-1836)

Notice

Ampere’s Law

B=0

B s

l

0

0

0 0

B s Bl NI

Bl NI

NB I nI

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

cosBA

cosBA

BA 0

GRAPHICAL INTERPRETATION OF MAGNETIC FLUX

The magnetic flux is proportionalto the number of field lines that passthrough a surface.

04/19/23Induction 64

65

iii

i AB )cos(

Add up all of these piecesthat are INSIDE the loop.

66

When you change the flux through a conducting loop, theCURRENT induced into the loop by this change willflow in such a way to create a flux change that opposesthe changing flux that is causing the current in the first place!

Change any or all of the◦ Bi

◦

◦ 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

iii

i AB )cos(

Don’t calculate the current … just the direction of the current and explain to the class!

+ Handout