The magnetic field · 磁场
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| magnetic field/mæɡˈnetɪk fiːld/ | 磁场 | cí chǎng |
| current/ˈkʌrənt/ | 电流 | diànliú |
| permanent magnets/ˈpɜːmənənt ˈmæɡnɪts/ | 永磁体 | yǒng cí tǐ |
| iron filings/ˈaɪən ˈfaɪlɪŋz/ | 铁屑 | tiě xiè |
| field lines/fiːld laɪnz/ | 场线 | chǎng xiàn |
| right-hand grip rule/raɪt hænd ɡrɪp ruːl/ | 右手定则 | yòu shǒu dìng zé |
| solenoid/ˈsəʊlənɔɪd/ | 螺线管 | luó xiàn guǎn |
| iron core/ˈaɪən kɔː/ | 铁芯 | tiě xīn |
| electromagnets/ɪˌlektrəʊˈmæɡnɪts/ | 电磁铁 | diàn cí tiě |
A field that ignores anything standing still
- Hold a stationary charge next to a powerful magnet and absolutely nothing happens. No force, no push, nothing.
- Set the same charge moving and it is suddenly shoved sideways, at right angles both to its motion and to the field.
- That selectivity is what makes a magnetic field different from an electric one, and it is the first thing the examiner asks you to state.
- This lesson is what a magnetic field 磁场 is, what produces one, and the field-line patterns you must be able to draw.
对静止之物毫不理会的场
- 把一个静止的电荷放在强磁铁旁边,什么也不会发生。没有力,没有推动,什么都没有。
- 让同一个电荷动起来,它立刻被侧向推开,方向同时垂直于它的运动和磁场。
- 这种挑剔正是磁场与电场的不同之处,也是考官要你首先说出的东西。
- 这一课讲什么是磁场(magnetic field)、什么产生它,以及你必须会画的场线图样。
What a magnetic field is
- A magnetic field is a region in which a force acts on a moving charge, a current-carrying conductor or a magnetic material.
- The mark scheme wants the word force and one of those three objects. "A region around a magnet" on its own scores nothing.
- Note what is missing: a charge at rest feels no magnetic force at all. An electric field acts on any charge; a magnetic field is choosy.
什么是磁场
- 磁场是这样一个区域:在其中运动电荷、载流导体或磁性材料受到力。
- 评分标准要"力"这个词,再加上那三样东西之一。单说"磁铁周围的区域"不得分。
- 注意缺了什么:静止的电荷完全不受磁力。电场作用于任何电荷;磁场则很挑剔。
A magnetic field is a region where: · 磁场是一个这样的区域：
Magnetic forces act only on moving · 运动 charges (and currents) — a charge at rest feels nothing. · 磁力仅作用于运动的电荷（及电流）——静止的电荷不受磁力。
A magnetic field is a region in which a force acts on which of these? Select all · 所有 that apply. · 磁场是对以下哪些对象施加力的区域？选择 所有 适用项。
A stationary charge feels no magnetic force at all, which is exactly what distinguishes a magnetic field from an electric one. · 静止的电荷完全不受磁力，这正是磁场区别于电场的特征。
What produces one
- Moving charges, which in practice means a current 电流 in a wire.
- Permanent magnets 永磁体, where the field comes from tiny atomic currents inside the material.
- Those are the same cause underneath. A permanent magnet is moving charge too, just on an atomic scale.
Iron filings 铁屑 turn an invisible field into something you can photograph
什么产生磁场
- 运动电荷,实际上就是导线中的电流(current)。
- 永磁体(permanent magnets),其中的场来自材料内部微小的原子电流。
- 归根到底这是同一个原因。永磁体也是运动电荷,只不过在原子尺度上。
铁屑(iron filings)把看不见的场变成可以拍照的东西
Which of these produce a magnetic field? · 下列哪些能产生磁场？
Moving charges and currents make magnetic fields; a permanent magnet does so via atomic currents. A still charge makes only an electric field. · 运动电荷和电流产生磁场；永磁体通过原子电流产生磁场。静止电荷仅产生电场。
Field lines
- Outside a magnet, field lines 场线 run from N to S, and from S to N inside it, so they always form closed loops.
- Lines never cross, and closer lines mean a stronger field. Every line carries an arrow.
- The lines are strongest, that is closest together, near the poles.
Closed loops, crowded at the poles
场线
- 在磁铁外部,场线(field lines)从 N 指向 S,在磁铁内部从 S 到 N,所以它们总是构成闭合回路。
- 线绝不相交,而线越密场越强。每条线都带箭头。
- 场线在磁极附近最强,也就是最密。
闭合的回路,在磁极处拥挤
Magnetic field lab · 磁场实验
Move between magnetic arrangements and see how field patterns change. · 在不同磁体排列间切换，观察磁场图案的变化。
Outside a magnet, the field lines run: · 磁铁外部，磁感线走向为：
Lines leave the N pole and enter the S pole outside, forming closed loops through the magnet. · 磁感线在外部从 N 极出发进入 S 极，并在磁铁内部形成闭合回路。
Magnetic field lines never cross. · 磁感线永不相交。
If they crossed, the field would point two ways at once — impossible. Closer lines just mean a stronger field. · 若相交，则该点磁场将指向两个方向——这是不可能的。线条越密表示场越强。
Field lines drawn closer together mean a ____ field. · 画得越密集的磁感线意味着 ____ 的磁场。
Line spacing shows strength — closer lines, stronger field. · 线条间距显示强度——线条越密，场越强。
Worked example: drawing the field of a straight wire
- Draw four field lines around a long straight wire carrying current into the page.
- The lines are concentric circles centred on the wire. That is the first mark.
- Their spacing increases with distance, because the field weakens as you move away. That is the second.
- Every line carries an arrow, and for current into the page the direction is clockwise, by the right-hand grip rule 右手定则: thumb along the current, fingers curl the way the field points.
例题:画直导线的磁场
- 画出通有流入纸面电流的长直导线周围的四条场线。
- 这些线是以导线为圆心的同心圆。这是第一分。
- 它们的间距随距离增大,因为场随着远离而减弱。这是第二分。
- 每条线都带箭头,而对流入纸面的电流,方向由右手定则(right-hand grip rule)给出是顺时针:拇指沿电流,四指弯曲的方向就是场的方向。
The patterns to know
- Bar magnet: curved lines from N to S outside, closest near the poles.
- Long straight wire: concentric circles, spacing widening with distance.
- Flat circular coil: the loops around the two sides reinforce through the centre, so the field there is at right angles to the plane of the coil and strongest at the centre. Seen from one face the coil is a north pole, from the other a south pole.
- Long solenoid 螺线管: many such coils in a row, so the field inside is nearly uniform and parallel to the axis, like a stretched bar magnet, and it falls off fast outside.
Uniform down the middle, and a bar magnet's field at the ends
要会的图样
- 条形磁铁:外部从 N 到 S 的弯曲线条,在磁极附近最密。
- 长直导线:同心圆,间距随距离变宽。
- 平面圆线圈:线圈两侧的回路在中心处相互加强,所以那里的场垂直于线圈平面,并在中心最强。从一面看线圈是北极,从另一面看是南极。
- 长螺线管(solenoid):许多这样的线圈排成一列,所以内部的场几乎均匀、平行于轴线,像一根拉长的条形磁铁,而在外部迅速减弱。
中间均匀,两端是条形磁铁的场
Drawing field lines round a straight wire is marked on which points? Select all · 所有 that apply. · 绘制直导线周围的磁感线涉及哪些要点？选择 所有 适用项。
Circles, widening spacing, arrows. For current into the page the direction is clockwise, by the right-hand grip rule. · 圆形、间距变宽、带箭头。对于流入纸面的电流，方向为顺时针，依据右手螺旋定则。
The iron core
- Putting an iron core 铁芯, or any ferrous material, inside a solenoid greatly increases the field.
- The reason, and this is the marked answer: the core becomes magnetised by the solenoid's field, and its own field adds to the field of the current.
- This is why electromagnets 电磁铁 and transformers are built around iron cores rather than air.
铁芯
- 在螺线管里放一个铁芯(iron core)或任何含铁材料,会大大增强磁场。
- 原因——这也是要评分的答案——是:铁芯被螺线管的场磁化,而它自己的场叠加到电流的场上。
- 这就是电磁铁(electromagnets)和变压器围绕铁芯而不是空气来制造的原因。
What is the magnetic field like inside a long solenoid? · 长螺线管内部的磁场是怎样的？
A solenoid is many coils in a row, so the field inside is uniform like a stretched bar magnet's, and it falls off fast outside. · 螺线管是一系列线圈，因此内部磁场如同拉长的条形磁铁般均匀，且在外部迅速衰减。
Match each arrangement to the shape of its magnetic field. · 将每种排列与其磁场形状匹配。
All four are worth being able to draw from memory, with arrows and with spacing that shows where the field is strong. · 这四种情况都值得能够凭记忆画出，并带有箭头和间距，以显示磁场强弱的位置。
Marks that slip away
- The definition needs the word force and one of: moving charge, current-carrying conductor, magnetic material. A stationary charge feels nothing.
- Field lines form closed loops: N to S outside, S to N inside. They never simply stop.
- A wire's field lines are concentric circles whose spacing widens, and each needs an arrow.
- An iron core works because it is magnetised and adds its own field, not because it "concentrates" or "attracts" the field.
容易丢掉的分
- 定义需要"力"这个词,加上以下之一:运动电荷、载流导体、磁性材料。静止的电荷什么也感受不到。
- 场线构成闭合回路:外部 N 到 S,内部 S 到 N。它们绝不会凭空中断。
- 导线的场线是间距变宽的同心圆,而且每条都需要箭头。
- 铁芯起作用是因为它被磁化并叠加自己的场,不是因为它"聚集"或"吸引"了磁场。
Why does an iron core greatly increase the field of a solenoid? · 为什么铁芯会极大地增强螺线管的磁场？
The core's atomic magnets line up and contribute their own field. That is the marked wording, and it is why electromagnets and transformers use iron cores. · 铁芯内的原子磁矩排列整齐并贡献自身磁场。这是标准表述，也是电磁铁和变压器使用铁芯的原因。
You've got it
- a magnetic field is a region where a force acts on a moving charge, a current-carrying conductor or a magnetic material; a stationary charge feels nothing
- it is produced by moving charges or by permanent magnets, which are atomic currents
- field lines run N to S outside and S to N inside, forming closed loops; they never cross, and closer means stronger
- patterns: bar magnet, concentric circles round a wire by the right-hand grip rule, a coil acting as a small magnet, and a solenoid uniform inside; an iron core is magnetised and adds its own field
你掌握了
- 磁场是运动电荷、载流导体或磁性材料受力的区域;静止电荷什么也感受不到
- 它由运动电荷或永磁体产生,而永磁体就是原子电流
- 场线外部从 N 到 S、内部从 S 到 N,构成闭合回路;它们绝不相交,越密越强
- 图样:条形磁铁、由右手定则确定的导线周围同心圆、像小磁铁一样的线圈,以及内部均匀的螺线管;铁芯被磁化并叠加自己的场