电磁学
Before someone study electricity and magnetism, some general questions arises, one of very important from those is how fluids flow, because there are many analogies between this and electrical circuits. We defined the flow rate of a fluid to be the amount of fluid that is delivered, divided by how long it took to deliver it. Fluids flow downhill because this lowers their potential energy: a height difference between two ends of a pipe gives rise to a pressure difference that makes the fluid go. The flow rate is also affected by the size of the pipe or tube carrying the fluid. The electrical equivalents to these are the electrical current (measured in amperes); the current flows because there is a potential difference (measured in volts); and the size of the current is affected by the resistance of the wire.
Electrical current stays inside conductors (such as wires). In order for an electrical device to work there has to be a path for the current: a circuit. Some electrical devices only work when the current flows the right way.
There are many electrical concepts have been studied in this aspect. Some important ones are:
•电线和导体。如果我们希望提供很多功率，我们必须使用非常好的导体的电线。
•电阻。这些是行为的元素，但不是很好。他们限制电流。电阻也是将电能转化为热量的机制。
•Incandescent light bulbs. These are really just resistors. But they deliver power to a tiny wire that gets so hot that it glows.
•开关。通过连接和断开电路的连接部分，我们可以影响哪些零件正在工作。
•电池。这些是将化学能转换为电能的设备。
•发光二极管。这是一种晶体管，它将电能直接转变为光线而无需使某些热点变热。因为它们比白炽灯灯泡更有效（且明亮），所以它们需要较少的电流才能运行。
•Capacitor. This is a device for storing electrical energy. They can't hold as much energy as a battery of similar size, but they are rechargeable indefinitely.
•Electromagnet. A current gives rise to a magnetic field, which we can make bigger by making a coil and by wrapping it around a steel or iron object.
•Buzzer. The kind we have in our kit combines an electromagnet with a circuit to turn the magnet on and off. It is one of several ways to make sound using an electrical signal.
•马达。通过打开和关闭磁铁，我们可以提供交替的力，使转子四处走动。
The above is the information on electricity now let us point out some views on magnetism. We found that there are materials that are themselves magnetic (permanent magnets), and materials that only become magnetic in the presence of other magnets. We can also produce a magnetic effect with a current carrying wire. A magnet gives rise to a field that surrounds them and which causes forces on other magnets, iron and steel objects, and current- carrying wires. The part of a magnet where the field emerges is called the N pole, and where the field enters the magnet is called the S pole. Magnets always have both N and S poles. It takes energy to make a magnetic field. We can use this idea to explain the magnetic force. When we turn off the current to an electromagnet, the magnetic energy will keep the current going briefly, and in the process may give rise to an unusually high voltage in the circuit or even a voltage in a different circuit.
电力在几种方面与磁性有关。电流产生磁场，磁场在电流上产生力。快速变化的磁场会产生电流流动的电效应。
它的一些主要主题是：
1.永久磁铁
2.法拉第的电磁诱导定律
3.Grouping of coils
4.Magnetic Flux
5.Self induction
6.产生诱导的e.m.f的各种方法
7.Electromagnetic Induction
8.Displacement current
9.Electromagnetic spectrum
10。History of electromagnetic waves
11. Main parts of electromagnetic spectrum
12.电磁波的事实
13.电磁波
14.Ammeter
15.电气和磁力的比较
16.回旋子
17.两个携带电流的平行导体之间的力
18.洛伦兹部队
19.运动的带电particle in a uniform magnetic field
20。Moving coil galvanometer
21。同步子
22。磁场上电流携带线圈上的扭矩
23.Velocity filter and mass spectrograph
24.Voltmeter
25.Aurora Boriolis
26.Forces in electric and magnetic field
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