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Chapter 30

Electromagnetic Induction

感应
感应
An emf is induced when the magnetic field in a coil is changed by pushing a bar magnet into or out of the coil. emfs of opposite signs are produced by ...
法拉第定律
法拉第定律
Faraday's law state that the induced emf is the negative change in the magnetic flux per unit of time. Any change in the magnetic field or change in ...
楞次定律
楞次定律
The direction in which the induced emf drives the current around a wire loop can be found through the negative sign. However, it is usually easier to ...
运动电动势
运动电动势
Magnetic flux depends on three factors: the strength of the magnetic field, the area through which the field lines pass, and the field's orientation ...
法拉第磁盘 Dynamo
法拉第磁盘 Dynamo
A Faraday disk dynamo is a DC generator, producing an emf that is constant in time. It consists of a conducting disk that rotates with a constant angular ...
感应电场
感应电场
The fact that emfs are induced in circuits implies that work is being done on the conduction electrons in the wires. What can possibly be the source of ...
感应电场:应用
感应电场:应用
An important distinction exists between the electric field induced by a changing magnetic field and the electrostatic field produced by a fixed charge ...
涡流
涡流
Since eddy currents occur only in conductors, magnets can separate metals from other materials. For example, in a recycling center, trash is dumped in ...
位移电流
位移电流
Ampère's law, in its usual form, does not work in places where the current changes with time and is not steady. Thus, Maxwell suggested including ...
位移电流的意义
位移电流的意义
A displacement current is analogous to a real current in Ampère's law, participating in Ampère's law the same way as the usual ...
电磁场
电磁场
Electric fields generated by static charges, often referred to as electrostatic fields, are characteristically different from electric fields created by ...
麦克斯韦电磁方程
麦克斯韦电磁方程
James Clerk Maxwell (1831–1879) was one of the major contributors to physics in the nineteenth century. Although he died young, he made major ...
麦克斯韦方程组中的对称性
麦克斯韦方程组中的对称性
Once the fields have been calculated using Maxwell's four equations, the Lorentz force equation gives the force that the fields exert on a charged ...
Ampere-Maxwell 定律:解决问题
Ampere-Maxwell 定律:解决问题
A parallel-plate capacitor with capacitance C, whose plates have area A and separation distance d, is connected to a resistor R and a battery of voltage ...
麦克斯韦方程组的微分形式
麦克斯韦方程组的微分形式
James Clerk Maxwell (1831–1879) was one of the significant contributors to physics in the nineteenth century. He is probably best known for having ...
发电机:交流发电机
发电机:交流发电机
Electric generators induce an emf by rotating a coil in a magnetic field. A simple alternator is an AC generator that creates electrical energy that ...
直流发电机
直流发电机
An alternator converts mechanical energy into electrical energy that varies sinusoidally, resulting in AC current. Meanwhile, a DC generator converts ...
反电动势
反电动势
Generators convert mechanical energy into electrical energy, whereas motors convert electrical energy into mechanical energy. A motor works by sending a ...
磁阻尼
磁阻尼
Eddy currents can produce significant drag on motion, called magnetic damping. For instance, when a metallic pendulum bob swings between the poles of a ...
超导体
超导体
A substance that reaches superconductivity, a state in which magnetic fields cannot penetrate, and there is no electrical resistance, is referred to as a ...
超导体的类型
超导体的类型
A superconductor is a substance that offers zero resistance to the electric current when it drops below a critical temperature. Zero resistance is not the ...
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