• 沒有找到結果。

# 8 磁場

N/A
N/A
Protected

Share "8 磁場"

Copied!
38
0
0

(1)

8 磁場

How is an aurora so thin yet so tall and wide?

(2)

### Introduction

How does magnetic resonance imaging (MRI) allow us to see details in soft nonmagnetic tissue?

How can magnetic forces, which act only on moving charges,

explain the behavior of a compass needle?

(3)

### The magnetic field

The electric field and the magnetic field

Electromagnets and permanent magnets

(4)

B

(N/C) (V m)

0

q E F

(5)

(6)

Figure 27.21

(7)

4

### gauss

108 T 1.5 T 10-2 T 10-4 T 10-10 T 10-14 T

(8)

### Magnetic Field Lines

Magnetic vs. electric dipoles

(9)

(10)

### 例 1 A 5.3 MeV proton

7

15

12 2

2 / 3.2 10 m/s sin 6.1 10 N / 3.7 10 m/s

B

B

v K m

F qvB a F m

  

  

  

B = 1.2 mT

(11)

### Discovery of the Electron

A cathode ray tube

Thomson’s procedure:

(12)

2 2

2 2

2 ,

/ ,

2

y qEL qE qvB mv

m B L v E B

q yE

### Calculation

2 2 2

2 2 , 1

x

x y

y

mv y QEL

t v L

t a y

m QE m

a F

the charge-to-mass ratio of the electron ：

1.75881961011 C·kg-1

(13)

### 8-3 Crossed Fields: The Hall Effect

By the conduction electrons in copper:

) (

d

l A Vle

n Bi

neA i ne

v J

B ev

eE

Ed V

d

d

(14)

### 例 2 A cube generator

mV 0

.

3

V

dvB V

Ed V

evB eE

d = 1.5 cm, v = 4.0m/s, B = 0.05T

(15)

qB m

v r

T

qB mv

r

r mv

qvB

r mv

ma F

/ 2

/ 2

/

/

/

2

2

### 

(16)

Figure 27.17a

(17)

Figure 27.17b

(18)

The frequency and angular frequency

2 2

1

m f qB

m qB

f T

### 頻率與軌跡

The magnetic bottle machine

(19)

### Helical Paths

cos 2 m p v T v

qB

The pitch (螺距) of the helical path cos sin

vv

vv

V and V

(20)

(21)

### 例 3 The Mass Spectrometer (質 譜儀)

2

2 1

/ 2

2

1 2

r x

q mV B

qB r mv

m qV

v

qV mv

(22)

u 93 .

8 203 2 2 2

2

2

V qx m B

q mV r B

x

Isotope Separation

Centrifuge and diffusion chamber

### 質譜儀

x = 1.6254m, V = 1000.0V, B = 80.000mT

(23)

### 8-5 Cyclotrons and Synchrotrons

Fermilab: 6.3km ring

### (迴旋加速器與同步加速器)

Tevatron Collider

Main Injector

(24)

The resonance condition:

When proton energy > 50Mev:

Out of resonance (relativistic effect)

A huge magnet (4×106 m2) is needed for high energy (500Gev) protons

The proton sychrotron at Fermilab can produces 1Tev proton

fosc

f

(25)

### CERN LHC

The LHC is 27km long and sits 100m below the surface.

(26)

Baryon fermion

Meson boson

(27)

(28)

B L

i F

iLB B

qv F

v iL

it q

B

d B

d

  

sin /

B

(29)

(30)

) (

2 2

cos

sin sin

) (

3 2

1

0

0 0

2

3 1

R L

iB F

F F

F

iBR iBR

d iBR

dF F

Rd iB

iBdL dF

iLB F

F

(31)

(32)

2

4

1

3

sin )

( sin

) 2 sin

( )

2 sin (

cos )

90

2 sin(

B NiA

N

iabB

iaB b iaB b

ibB ibB

F

 

 

N turns coil

(33)

### 例 5 A galvanometer for analog meters

-6 -4 2

8

sin sin

[(250)(100 10 A)(2.52 10 m ) (0.23T)(sin 90 )] / 28

5.2 10 N m / degree NiAB

NiAB

 

(34)

(35)

Figure 27.40

(36)

) :

cf (

sin

E p

B

B

NiA    

    

) (

)

( p E U B

U

     

 

  

(37)

B

B B

U

2

) (

) (

### 磁能

(38)

The student with the open book will choose one of the questions listed in Activity 7 and write notes related to answering the question.. The student who does not have a book will

Play the audio track for Activity 6, and have students match the given questions with one of the responses they hear.. These questions and responses are meant to provide

Play the audio track for Activity 6, and have students match the given questions with one of the responses they hear.. These questions and responses are meant to provide

Set a time limit for students to complete the reading and work through the Reading Comprehension and Language Practice activities.. At the end of the allotted time, have students

Set a time limit for students to complete the reading and work through the Reading Comprehension and Language Practice activities.. At the end of the allotted time, have students

A limited section of a reading text (usually a short paragraph) is used for students to practice stress and intonation of a previously read passage.. With limited use, students

Functional brain mapping by blood oxygenation level-dependent contrast magnetic resonance imaging. Functional MRI A Introduction to

How would this task help students see how to adjust their learning practices in order to improve?..