Electricity and Magnetism Demonstrations

电磁学演示

Moving a magnet into a coil of wire will generate a voltage in that coil according to Faraday's Law. The magnitude of the voltage is proportional to the rate of change of magnetic flux in the coil, so that moving the magnet in faster will produce a greater voltage. The polarity of the voltage is such that it opposes the change that produces it, so pulling the magnet out will produce a voltage of the opposite polarity.

将磁体插入线圈时，根据法拉第定律，线圈中会产生电压。电压的大小与线圈中磁通量的变化率成正比，因此将磁体插入得更快会产生更大的电压。电压的极性是这样的，它会抵消产生该变化的磁体运动，因此将磁体拉出时会产生相反极性的电压。

A copper rod is placed in the magnetic field of a permanent magnet. If a battery is used to drive an electric current through the rod, it will experience a force perpendicular to the magnetic field in the direction given by the right-hand rule. A double-pole switch is used to switch the current to the opposite direction to show that the force on the wire reverses.

一根铜棒被放置在永磁体的磁场中。如果用电池使电流通过棒，它将受到一个垂直于磁场的力，方向由右手法则确定。双极开关用于将电流方向切换为相反方向，以显示作用在导线上的力也会反转。

When ordinary AC voltage is applied to a large coil of wire with an iron core, a strong alternating magnetic field is produced. If an aluminum ring is placed over the core and 120 volts AC is connected, a large current is induced in the ring according to Faraday's Law and it is tossed into the air. Note that if the magnetic field on the aluminum ring were perfectly vertical, the magnetic force by the right-hand rule would be radially inward and outward on the ring - and if you hold the ring down, you can hear it hum at 60Hz from that alternating force. But at the location where the magnetic field exits the coil, it diverges and will have radially outward and inward components.The force resulting from those components are upward and downward on the ring. The first upward force pulse will launch the ring into the air. At the end of the video is the contrast with a ring with a slot cut into it so that no circulating induced current is produced.

当普通交流电压加到一个带有铁芯的大线圈上时，会产生一个强的交变磁场。如果将一个铝环放在铁芯上，并连接120伏交流电，根据法拉第定律，环中会产生一个大的电流，并会被抛起。注意，如果铝环上的磁场完全垂直，根据右手定则，磁场力将向环内和向外作用——如果你把环压住，可以听到由于这种交变力而发出的60Hz的嗡嗡声。但在磁场从线圈退出的地点，磁场会发散，并具有径向向外和向内的分量。这些分量产生的力将向上和向下作用于环上。第一个向上的力脉冲将把环抛入空中。视频结尾展示了与一个被切去槽的环的对比，后者没有产生环形感应电流。

A large coil of wire with an iron core can produce a large alternating magnetic field in the air, particularly around the iron core because of its ferromagnetic nature. This alternating magnetic field is sufficient to light a lightbulb attached to another coil of wire when that alternating magnetic field is allowed to pass through the coil. This is another example of Faraday's Law and includes the principles used in transformers. Moving the coil and bulb around the end of the iron core allows you to visualize the geometry of the alternating magnetic field from the coil.

一个带有铁芯的线圈可以在空气中产生较强的交变磁场，特别是在铁芯周围，这是因为铁的铁磁性。这种交变磁场足以使连接到另一个线圈的灯泡发光，当该交变磁场通过另一个线圈时。这也是法拉第电磁感应定律的一个例子，包含了变压器所用的原理。将线圈和灯泡移动到铁芯末端，可以更直观地观察线圈产生的交变磁场的几何形状。