18.2 磁场

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  磁场

  

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  Powerful electromagnets are commonly used for industrial lifting. Here, a is lifting  heavy steel pipes  and unloading them onto a warehouse floor . Other uses for lifting magnets include moving cars in a junk yard, lifting rolls of steel sheeting, and lifting large steel parts for various machines. Electromagnets are usually used for these jobs because they are magnets only when the electric current is on. The magnet will hold the iron object when the current is on and release it when the current is off.
  ::工业提升通常使用强大的电子磁铁。 这里, 一个将重钢管举起并卸到仓库地板上。 其他的磁铁提升用途包括: 在垃圾场内移动汽车, 抬起钢板卷, 为各种机器搬起大块钢块。 电磁铁通常用于这些工作, 因为它们只有在电流打开时才是磁铁 。 磁铁将在电流打开时屏住铁体, 当电流关闭时释放它 。

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  Electric Currents and Magnetic Fields
  ::电流和磁场

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  Electricity and magnetism are inextricably linked. Under certain conditions, electric current causes a magnetic field. Under other conditions, a magnetic field can cause an electric current. A moving charged particle creates a magnetic field around it. Additionally, when a moving charged particle moves through a different magnetic field, the two magnetic fields will interact. The result is a force exerted on the moving charged particle. 
  ::电流和磁力密不可分。 在某些条件下, 电流会引发磁场。 在其他条件下, 磁场会引发电流 。 移动带电的粒子会围绕电流产生磁场 。 此外, 当移动带电的粒子穿过不同的磁场时, 两个磁场会相互作用。 结果是对移动带电的粒子施加了压力 。

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  Magnetic Field Around a Current Carrying Wire
  ::环绕当前携带电线的磁场

  

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  In sketch (a) above, a current is being pushed through a straight wire. Small compasses placed around the wire point in a circle, instead of all towards the north pole. This demonstrates the presence of a magnetic field around the wire. If the current is turned off, the compass points return to pointing north. 
  ::在上文的草图(a)中,电流正在通过直线线推动。小指南针在一个圆圈中围绕电线点放置,而不是全部朝向北极。这表明电线周围存在磁场。如果电流被关闭,指南针指向北点。

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  The current moving in a straight wire produces a circular magnetic field around the wire. When using conventional current , the direction of the magnetic field is determined by using the  right hand rule . The rule says to curl your right hand around the wire such that your thumb points in the direction of the conventional current. Having done this, your fingers will curl around the wire in the direction of the magnetic field. Note that the right hand rule is for conventional current. Remember that electrons flow in the opposite direction of conventional current. If you want to determine the direction of the magnetic field based on the direction of electron flow, you will have to use your left hand instead of your right, with your thumb pointing in the direction of electron flow. If you try this you can see that both methods show the same direction for the magnetic field.
  ::直线线下移动的电流将产生一个圆形磁场。 当使用常规电流时, 磁场的方向会由右手规则来决定。 规则要求将右手围绕电线弯曲, 从而将拇指指指向常规电流的方向。 这样做后, 您的手指会围绕电线弯曲到磁场的方向。 请注意, 右手规则是常规电流的。 记住, 电子会向常规电流的相反方向流动。 如果您想要根据电流的方向确定磁场的方向, 您必须使用左手而不是右手, 您的拇指指向电子流的方向。 如果您尝试这样做, 您可以看到两种方法都显示磁场的同一方向 。

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  Charged Particles Moving Through a Magnetic Field
  ::通过磁场移动的充电粒子

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  When a charged particle moves through a magnetic field at right angles to the field, the field exerts a force on the charged particle in a different direction.
  ::当带电粒子从右角度从磁场向田地移动时,该场对带电粒子按不同方向施压。

  

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  In the case sketched above, an electron is moving downward through a magnetic field. The motion of the electron is perpendicular to the magnetic field. The force ( $\begin{align*}F\end{align*}$ ) exerted on the electron can be calculated by the equation,
  ::在上文所描绘的案例中,电子正在通过磁场向下移动。电子的动作与磁场垂直。对电子施加的力(F)可以通过方程式计算,

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  $\begin{align*}F=Bqv\end{align*}$
  ::F=Bqv =Bqv

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  where  $\begin{align*}v\end{align*}$  is the of the particle in meters per second and q is the charge on the particle in coulombs. The term  $\begin{align*}B\end{align*}$  represents the strength of the magnetic field in teslas. A tesla is equal to  $\begin{align*}1\frac{newton}{ampere\cdot meter}\end{align*}$ and is a unit named after the Serbian physicist Nikola Tesla. An ampere is equivalent to  $\begin{align*}1\frac{coulomb}{second}\end{align*}$  and you can see in the equations below that the units on the side of the equation cancel out to leave us with newtons, the unit of force.
  ::V 是每秒以米计的粒子, q 是 coulombs 中的粒子的充电。 B 表示 Teslas 中的磁场强度。 Tesla 等于 1 牛顿ampere 计, 以塞尔维亚物理学家 Nikola Tesla 命名 。 ampere 等于 1 coulomb 秒, 您可以在下面的方程式中看到, 方程式侧面的单位取消后, 给我们留下牛顿, 即力单位 。

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  $\begin{align*}F=Bqv\end{align*}$
  ::F=Bqv =Bqv

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  $\begin{align*}F=\frac{newton}{amp\cdot meter}\times coulomb\times \frac{meter}{second}\end{align*}$
  ::F=newtonamp 米xcoulombx 秒

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  Replacing amperes with  its unit definition:  
  ::以其单位定义取代氨:

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  $\begin{align*}F=\frac{newton\cdot second}{coulomb\cdot meter}\times coulomb\times \frac{meter}{second}\end{align*}$
  ::F=newton 秒库伦 公尺x公尺

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  Cancelling units:
  ::取消单位 :

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  $\begin{align*}F=\frac{newton\cdot \cancel{second}}{\cancel{coulomb}\cdot \cancel{meter}}\times \cancel{coulomb}\times \frac{\cancel{meter}}{\cancel{second}}\end{align*}$
  ::F=newton 秒库伦 公尺x公尺

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  $\begin{align*}F=newtons\end{align*}$
  ::F=新顿

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  Again, we can determine the direction of the force acting upon the electron using a hand rule. Since the electron has a negative charge, the left hand rule is used. The fingers of the left hand are pointed in the direction of the magnetic field and the thumb points in the direction of the initial electron movement. The direction of the force acting on the electron is the direction the palm of the left hand faces. The direction of the magnetic field, the direction of the moving charge, and the direction of the force on the particle are all perpendicular to each other.
  ::同样,我们可以用手法确定电磁对电动的动向。由于电子有负电荷,使用左手法则。左手法则。左手手指指向磁场的方向,拇指指向初始电子运动的方向。电磁力指向左手面的手掌方向。磁场的方向、移动电荷的方向和粒子的力向都是相互垂直的。

  

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  In most situations, a positive test charged is used, instead of an electron. In these circumstances, the right hand rule  is used. The right hand rule is the same as the left hand rule; the thumb is the direction of initial charge movement, the fingers are the direction of the field, and the palm is the direction of the acting force. 
  ::在多数情况下,使用正数测试而不是电子。在这种情况下,使用右手规则。右手规则与左手规则相同;拇指是初始电荷运动的方向,手指是田地的方向,手掌是动作力的方向。

  

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  In dealing with the relationships that exist between magnetic fields and electric charges, there are both left hand and right hand rules that we use to indicate various directions – directions of fields, directions of currents, directions of motion. To avoid errors, it is absolutely vital to know and express whether the system we are observing is using conventional current or electron current. This allows us to use the appropriate rule.
  ::在处理磁场和电费之间的关系时,我们用左手和右手规则来表示不同的方向 — — 字段方向、电流方向、运动方向。 为了避免错误,绝对必须知道和表达我们观察的系统是使用常规的电流还是电流。 这使我们能够使用适当的规则。

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  Example 1  
  ::例1

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  An electron traveling at  $\begin{align*}3.0 \times 10^6 \ m/s\end{align*}$ passes through a  $\begin{align*}0.0400 \ N/amp \cdot m\end{align*}$ uniform magnetic field. The electron is moving at right angles to the magnetic field. What force acts on the electron?
  ::以3.0×106 mm/s/s进行移动的电子通过0.0400 N/ampm统一的磁场。电子正从右角度移动到磁场。电子上有什么作用?

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  $\begin{align*}F=Bqv=(0.0400 \ N/amp \cdot m)(1.6 \times 10^{-19} \ C)(3.0 \times 10^6 \ m/s) \end{align*}$
  ::F=Bqv=(0.00400 N/ampm)(1.6×10-19 C)(3.0×106 m/s)

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  $\begin{align*}=1.9 \times 10^{-14} \ N\end{align*}$
  ::=1.9×10-14 N

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  When the current is traveling through a magnetic field while inside a wire, the magnetic force is still exerted but now it is calculated as the force on the wire rather than on the individual charges in the current.
  ::当电流在电线内穿过磁场时,磁力仍然在施加,但现在计算为电线上的力量,而不是电流中的个别电荷。

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  The equation for the force on the wire is given as $\begin{align*}F = BIL\end{align*}$ , where B  is the strength of the magnetic field, I  is the current in amps and L  is the length of the wire in and perpendicular to the field.
  ::线上力的方程式是F=BIL,B是磁场的强度,I是Amps的电流,L是与田间相连的电线的长度。

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  Example 2  
  ::例2

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  A wire 0.10 m long carries a current of 5.0 A. The wire is at right angles to a uniform magnetic field. The force the field exerts on the wire is 0.20 N. What is the magnitude of the magnetic field?
  ::一条0.10米长的电线带有5.0A的电流。 电线位于一个统一的磁场的正确角度。 电线的电力是0. 20 N。 磁场的大小是多少?

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  $\begin{align*}B=\frac{F}{IL}=\frac{0.20 \ N}{\left(5.0 \ A \right) \left(0.10 \ m\right)}=0.40 \ \frac{N}{A \cdot m}\end{align*}$
  ::B=FIL=0.20 N(5.0 A)(0.10米)=0.40 NAm

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  In a particle accelerator, a strong magnetic field is used to exert a force on moving particles in a direction perpendicular to their motion. As a result, the particles begin to travel in a circle. Scientists can measure the radius of these circles and use them to distinguish the type of particle (electron, proton , neutrino, muon, etc). Different particles will have different masses and charges, and so will interact with the magnetic field in different ways. Use the Particle Tracks simulation below to learn more:
  ::在粒子加速器中,一个强大的磁场被用来对将粒子移动到与其运动相垂直的方向施加一种力力。 因此,粒子开始在圆圈中移动。 科学家可以测量这些圆圈的半径, 并用它们来区分粒子的类型( 电子、 质子、 中微子、 介子等 )。 不同的粒子将具有不同的质量和电荷, 从而以不同的方式与磁场发生相互作用。 使用下面的粒子轨迹模拟来学习更多 :

   

   

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  Summary
  ::摘要

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  • A moving charged particle creates a magnetic field around it.
    ::一个移动的加热粒子围绕它产生磁场。
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  • Charge through a wire creates a magnetic field around it, the properties of which can be determined using a right hand rule.
    ::电线通过电线充电,围绕电线产生磁场,其特性可通过右手规则确定。
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  • When a moving charged particle moves through another magnetic field, that field will exert a force on the moving charged particle that can be expressed using  $\begin{align*}F = Bqv\end{align*}$ .
    ::当移动中带电粒子穿过另一个磁场时,该字段将对移动中带电粒子施加一种力,可以用 F=Bqv 表示。
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  • The relationships between the moving charged particle, magnetic field, and the force exerted can be determined using the right hand rule if the particle is positive, or the left hand rule if it is negative.
    ::移动带电粒子、磁场和所施力之间的关系,如果粒子呈阳性,可使用右手规则确定,如果呈阴性,可使用左手规则确定。
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  • When the current is traveling through a magnetic field while inside a wire, the magnetic force is still exerted but now it is calculated as the force on the wire rather than on the individual charges in the current, calculated using  $\begin{align*}F = BIL\end{align*}$ .
    ::当电流在铁丝网内穿过磁场时,磁力仍然有效,但现在用F=BIL计算,用电线的力量而不是电流中的个别电荷计算。

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  Review
  ::回顾

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  1. Find the force on a 115 m long wire at right angles to a  $\begin{align*}5.0 \times 10^{-5} \ N/A \cdot m\end{align*}$ magnetic field, if the current through the wire is 400. A.
     ::如果通过电线的电流为400,则从右角度在115米长的电线上找到力到5.0×10-5 N/Am磁场。
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  2. Find the force on an electron passing through a 0.50 T magnetic field if the velocity of the electron is $\begin{align*}4.0 \times 10^6 \ m/s \end{align*}$ .
     ::如果电子速度为4.0×106 m/s,则在通过0.50 T磁场的电子上发现强度。
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  3. A stream of doubly ionized particles  $\begin{align*}(\text{charge}= 2+)\end{align*}$ moves at a velocity of  $\begin{align*}3.0 \times 10^4 \ m/s\end{align*}$ perpendicularly to a magnetic field of 0.0900 T. What is the magnitude of the force on the particles?
     ::以3.0×104 m/s/s 垂直速度移动到 0.0900 T 的磁场上。 粒子的强度是多少?
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  4. A wire 0.50 m long carrying a current of 8.0 A is at right angles to a 1.0 T magnetic field. What force acts on the wire?
     ::一条长0.50米长的电线,载有8.0A的电流,在1.0T磁场的右角度。
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  5. Suppose a magnetic field exists with the north pole at the top of the computer monitor and the south pole at the bottom of the monitor screen. If a positively charged particle entered the field moving from your face to the other side of the monitor screen, which way would the path of the particle bend?
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     1. left
        ::左左
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     2. right
        ::右右右右右
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     3. up
        ::上上
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     4. down
        ::向下下下
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     5. none of these
        ::没有任何这些
     
     ::假设在计算机显示器顶部的北极和显示器屏幕底部的南极极存在磁场。如果一个正充电的粒子从你的脸部进入显示器另一侧的田地,那么粒子弯曲的路径会走哪条路呢?
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  6. Suppose the surface of your dining room table is a magnetic field with the north pole at the north edge and the south pole at the south edge. If an electron passes through this field from ceiling to floor, which way will the path of the electron bend?
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     1. west
        ::西 西
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     2. east
        ::东东
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     3. north
        ::北北部
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     4. south
        ::南南
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     5. toward the ceiling
        ::最高至最高
     
     ::假设你的餐桌表面是磁场,北边是北极,南边是南边是南边是南边。如果电子从天花板穿过这个田地,电子弯道会走哪条路呢?往南以西向南,向北。

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  Explore More
  ::探索更多

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  Use this resource to answer the questions that follow.
  ::使用此资源回答下面的问题 。

   

   

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  1. What happens to the wire when the current begins to flow?
     ::当电流开始流动时电线会怎样?
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  2. What difference would it make if the magnetic field were stronger?
     ::如果磁场更强又有什么区别呢?
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  3. What difference would it make if the battery were 3.0 V instead of 1.5 V?
     ::如果电池是3.0V而不是1.5V,有什么区别?