第20章磁性Magnetism原書 p.669–710
Section Summary節のまとめ
20.1 Magnetic Fields, Field Lines, and Force20.1 磁場、磁力線、力
• All magnets have two poles: a north pole and a south pole. If the magnet is free to move, its north pole orients itself toward the geographic North Pole of Earth, and the south pole orients itself toward the geographic South Pole of Earth.• A repulsive force occurs between the north poles of two magnets and likewise for two south poles. However, an attractive force occurs between the north pole of one magnet and the south pole of another magnet.• A charged particle moving through a magnetic field experiences a force whose direction is determined by the right-hand rule.• An electric current generates a magnetic field.• Electromagnets are magnets made by passing a current through a system of wires.
・どんな磁石も二極——N極とS極——を持つ。磁石が自由に動けるなら、そのN極は地球の地理上の北極のほうへ、S極は地球の地理上の南極のほうへ向く。・二つの磁石のN極どうしの間には斥力が起こり、S極どうしも同様である。しかし一方の磁石のN極ともう一方のS極の間には引力が起こる。・磁場の中を動く帯電した粒子は、右手の法則で向きの決まる力を受ける。・電流は磁場を作る。・電磁石とは、導線の仕掛けに電流を流して作る磁石である。
20.2 Motors, Generators, and Transformers20.2 電動機、発電機、変圧器
• Electric motors contain wire loops in a magnetic field. Current is passed through the wire loops, which forces them to rotate in the magnetic field. The current is reversed every half rotation so that the torque on the loop is always in the same
・電動機は磁場の中に導線の輪を含む。導線の輪に電流を流すと、輪は磁場の中で回らされる。輪にはたらくトルクがつねに同じ向きになるように、
magnetic flux component of the magnetic field perpendicular to the surface area through which it passes and multiplied by the area
磁束 磁場のうち、通り抜ける面積に垂直な成分に面積をかけたもの
magnetic pole part of a magnet that exerts the strongest force on other magnets or magnetic material
磁極 磁石が他の磁石や磁性の材料に最も強い力を及ぼす部分
magnetized material that is induced to be magnetic or that is made into a permanent magnet
磁化した 磁性を帯びさせられた、あるいは永久磁石にされた材料
north pole part of a magnet that orients itself toward the geographic North Pole of Earth
N極 地球の地理上の北極のほうへ向く磁石の部分
permanent magnet material that retains its magnetic behavior for a long time, even when exposed to demagnetizing influences
永久磁石 磁性を失わせる働きにさらされても長いあいだ磁石としてのふるまいを保つ材料
right-hand rule rule involving curling the right-hand fingers from one vector to another; the direction in which the right thumb points is the direction of the resulting vector
右手の法則 右手の指をあるベクトルから別のベクトルへ丸める法則。右手の親指が指す向きが、生じるベクトルの向きである
solenoid uniform cylindrical coil of wire through which electric current is passed to produce a magnetic field
ソレノイド 磁場を作るために電流を流す、一様な円筒形の導線のコイル
south pole part of a magnet that orients itself toward the geographic South Pole of Earth
S極 地球の地理上の南極のほうへ向く磁石の部分
transformer device that transforms voltages from one value to another
変圧器 電圧をある値から別の値へ変える装置
direction.• Electric generators contain wire loops in a magnetic field. An external agent provides mechanical energy to force the loops to rotate in the magnetic field, which produces an AC voltage that drives an AC current through the loops.• Transformers contain a ring made of magnetic material and, on opposite sides of the ring, two windings of wire wrap around the ring. A changing current in one wire winding creates a changing magnetic field, which is trapped in the ring and thus goes through the second winding and induces an emf in the second winding. The voltage in the second winding is proportional to the ratio of the number of loops in each winding.• Transformers are used to step up and step down the voltage for power transmission.• Over long distances, electric power is transmitted at high voltage to minimize the current and thereby minimize the Joule losses due to resistive heating.
半回転ごとに電流が反転される。・発電機は磁場の中に導線の輪を含む。外部の作用者が力学的エネルギーを与えて輪を磁場の中で回し、それが交流の電圧を作って輪に交流の電流を流す。・変圧器は磁性の材料でできた環を含み、環の反対側に導線の巻きが二つ環に巻かれている。一方の導線の巻きで電流が変わると変わる磁場ができ、それが環に閉じ込められて二つ目の巻きを通り、二つ目の巻きに起電力を誘導する。二つ目の巻きの電圧は、それぞれの巻きの巻き数の比に比例する。・変圧器は送電のために電圧を上げ下げするのに使われる。・長距離では、電流を最小にして抵抗の発熱によるジュール損を最小にするために、電力は高電圧で送られる。
20.3 Electromagnetic Induction20.3 電磁誘導
702• Faraday’s law of induction states that a changing magnetic flux that occurs within an
・ファラデーの誘導の法則は、導体の輪が囲む面積の中で
area enclosed by a conducting loop induces an electric current in the loop. • Lenz’ law states that an induced current flows in
磁束が変われば輪に電流が誘導されると述べる。 ・レンツの法則は、誘導電流が