(nm02) Magnetic Field 磁場 (I)


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  1. Marks to date: Review and See Web

Review: Right Hand Rules

From electric to magnetic fields

ElectricMagnetic
magnetic fieldNO
Dipole with many electric lines Bar Magnet with Field Lines
For both, closeness of lines indicate strength of the field.
From +ve → -ve Complete circle -- outside: N→S inside: S→N
Draw Equipotential LinesMagnetic Potential is a Vector

Key Points

Fields: Electric & Magnetic
Point $$ \mathbf { \vec E }_{point} = {1 \over {4 \pi \epsilon_o}} \, \color{fuchsia} {q \over r^2} \, \mathbf {\hat r } $$ $$ \mathbf { \vec B }_{point} = {\mu_o \over {4 \pi}} \, \color{fuchsia} {q \over r^2} \, \mathbf {\color{fuchsia} {\vec v}} \times \mathbf {\hat r } $$
Moment $$ \mathbf {\vec p} = q \, \mathbf {\vec s} $$ $$ \mathbf {\vec \mu} = I \, \mathbf {\vec A} $$
Dipoles (Farfield) $$ \mathbf{ \vec E}_{on \,axis} = {1 \over {4 \pi \epsilon_o}} \, \color{fuchsia} {2 \mathbf {\vec p} \over z^3} \mathbf {\hat z} $$ $$ \mathbf{ \vec B}_{on \,axis} = {\mu_o \over {4 \pi}} \, \color{fuchsia} {2 \mathbf {\vec \mu} \over z^3} \mathbf {\hat z}$$
Cylinder $$ \lambda \, [C m^{-1}] $$ $$ I \, [C s^{-1} = A] $$
$$ \mathbf {\vec E}_{line,\infty} = {1 \over {4 \pi \epsilon_o}} \, \color{fuchsia}{2 \lambda \over r} \, { \mathbf {\hat r }} $$ $$ \mathbf {\vec B}_{wire,\infty} = {\mu_o \over {4 \pi}} \, \color{fuchsia}{2 I \over r} \, { \mathbf {\hat \theta }} $$
Gauss & Ampere $$ \iint \mathbf {\vec E} \, \cdot d \mathbf {\vec A} = {Q \over \epsilon} $$ $$ \oint \mathbf {\vec B} \, \cdot \, d \, \mathbf {\vec s} = {\mu_o I} $$
Lorentz$$ \mathbf a = { m_g \over m_e} \mathbf {\vec G} + { q \over m_e} \mathbf {\vec E} + { q \over m_e} \mathbf {\vec v} \times \mathbf {\vec B} $$
WorkYES!NO!

Lecture Power Points

Knight vs4 chapter 29 Knight vs3 chapter 32 (to Slide 44)

Further Study...

  1. Magnet making Current Explain result in pictures like writing scientific paper
  2. Electric and Magnetic Forces don't exist: It is Electro-Magnetic Force
  3. What forces are real? (break time)

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C G White (白愛恩), J D White (白小明)
baixiaoming AT gmail.com