2. What is the Hall effect? What is the Rogowski coil?
The Hall effect is a phenomenon in which a lateral potential difference occurs across a current-carrying conductor in a magnetic field.
Rogowski coil is a kind of electromagnetic induction principle and the use of the full current law, measuring large inrush current (tens of kA to several hundred KA) or the rate of change of impact of the current.
3, What is Poynting vector?
The Poynting vector is the cross product of the electric field strength and the magnetic field strength, and the direction represents the direction of energy flow, and the size represents the unit time
The energy per unit vertical area. The unit is watts per square meter.
Poynting's theorem is the energy conservation theorem in the electromagnetic field, which means that the energy transfer is equal to the reduction of energy stored and the algebraic sum of the power supplies.
4, What is the the difference between free charge and bound charge, dielectric polarization and electrostatic induction and types?
Free charge is a free electron in the conductor (metal), ion (gas or liquid) and so on when the electric field force let the free movement of the charge. Bounded charge is defined as a charged particle in a dielectric that is bound by an atomic force, an intra molecular force, or an inter molecular bond,
They can move a little under the force of an electric field, but can not leave the range of molecules.
Polarization of the dielectric refers to the electric field in the dielectric molecules or atoms to form electric dipoles, the surface of the dielectric appears positive
And the phenomenon of negative binding charge. After polarization, the electric field created by the bound charge in the dielectric can generally attenuate the applied electric field.
Electrostatic induction of a conductor refers to the free-charge movement of the conductor in an applied electric field, accumulating on the surface of the conductor and establishing an electric field until The surface charge of the electric field and the external electric field in the conductor everywhere is the phenomenon. Due to electrostatic induction, electrostatic field In the conductor is internally charged, the charge can only be distributed in the conductor surface; charge inside the conductor is zero; its just near the conductor surface field strength and the surface perpendicular to the conductor is an equipotential body, the conductor surface is equipotential surface.
5, What is the difference between electrostatic shielding electromagnetic shielding?
Electrostatic shielding is the use of electrostatic equilibrium of electric field within the field strength of the conductor is made zero for shielding device.
Electromagnetic shielding is the use of good conductors in the vortex that can prevent high-frequency electromagnetic waves into this conductor that can be made while shielding the electric field and Magnetic field shielding device. It can suppress radiated interference and high-frequency conducted interference.
Magnetostatic shielding is the use of magnetic field in the high magnetic flux law of ferromagnetic materials that can make most of the magnetic field concentrated in the ferromagnetic circuit. A shielded device is provided which can shield the magnetic field.
The effect of static shielding is similar to that of electrostatic shielding, but the effect is not good for static shielding, since the conductivity of the metal conductor is of several dozen orders of magnitude than the air conductivity , and ferromagnetic material and air permeability difference of only a few orders of magnitude.
6, given the second type of boundary conditions, why the potential value of uncertainty?
Only partial derivatives do not have a base value
7, E at the interface between the two media is changing?
Tangent direction E unchanged; normal direction D unchanged.
8, In a circular coil vertical through a current into the wire, there is no induced coil emf
This depends on whether or not there is a change in the incoming current, since the principle of the induced electromotive force is that the induced magnetic field produces an induced electric field,
If there is a change in the current coil is induced electromotive force, if the current does not change then it is not.
9, In a balloon, the surface covered with a uniform charge, with the balloon constantly blowing large balloons inside and outside the electric field are how to change?
External constant, the internal field strength is zero
10, For the stability of the electromagnetic field conditions, physical significance When the frequency of the alternating current is low?
it is much smaller in the vicinity of the current than the wavelength of the electromagnetic wave at that frequency in the vacuum, Of the region, you can ignore the delayed effect of electromagnetic fields, such areas of the electromagnetic field is a quasi-stable or quasi-stable field).
