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GRE Subject Test · GRE Physics 주제 29 5:59 영어 내레이션 · 영어 + 중국어 자막 burned-in
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Sliding a dielectric into a capacitor changes the field one way if the battery has been disconnected and another way if it is still connected.
把电介质推入电容器时，如果电池已断开，电场会以一种方式变化；如果电池仍然连着，则以另一种方式变化。
This topic relates free and bound charge to D, E and the polarisation, compares fixed charge with fixed voltage, and treats magnetisation and the boundary conditions.
本主题把自由电荷和束缚电荷与 D、E 和极化强度联系起来，比较电荷固定与电压固定的情形，并讨论磁化强度和边界条件。
Polarisation P is the dipole moment per unit volume.
极化强度 P 是单位体积的偶极矩。
D is defined as epsilon naught E plus P, so its divergence counts only free charge, while E still feels all charge, bound charge included.
D 定义为 ε0 E 加 P，因此它的散度只计入自由电荷，而 E 仍然感受到全部电荷，包括束缚电荷。
A uniform P leaves no bound charge inside, but puts opposite bound charges on the two faces.
均匀的 P 在内部不产生束缚电荷，但在两个表面上产生符号相反的束缚电荷。
A dielectric is not a metal: the field inside it is reduced, not zero.
电介质不是金属：其内部电场被减弱，而不是为零。
For a linear isotropic dielectric, P equals epsilon naught chi e E and D equals epsilon E with epsilon equals epsilon naught times 1 plus chi e which equals epsilon naught epsilon r.
对于线性各向同性电介质，P等于ε₀χₑE，D等于εE，其中ε等于ε₀乘以(1+χₑ)，即ε₀εᵣ。
These simple scalar relations assume the response is linear and ignore anisotropy, strong dispersion and nonlinear effects.
这些简单的标量关系假设响应是线性的，并忽略了各向异性、强色散和非线性效应。
In a fully filled, large parallel-plate capacitor with negligible edge effects, D normal to the plates equals the free surface-charge density.
在充满介质的、边缘效应可忽略的大平行板电容器中，垂直于极板的D等于自由面电荷密度。
If sigma free stays fixed, increasing epsilon reduces E equals sigma free divided by epsilon.
若σ_free保持不变，增大ε会降低E，即σ_free除以ε。
The bound charges oppose the applied field; their magnitude is not automatically equal to the free plate charge.
束缚电荷与外加电场方向相反；其大小并不自动等于极板上的自由电荷。
For plate area A and spacing d, C equals epsilon A divided by d.
对于极板面积A和间距d，电容C等于epsilon乘以A除以d。
Disconnecting the battery fixes free charge Q: V equals Q over C falls, and stored energy U equals Q squared divided by 2C falls when a dielectric increases C.
断开电池后自由电荷Q固定：电压V等于Q除以C会下降，储存能量U等于Q平方除以2C也会下降，这是因为电介质使电容C增大。
Leaving an ideal voltage source connected fixes V: Q equals C times V and stored energy U equals C times V squared divided by 2 both rise.
若保持理想电压源连接，则电压V固定：电荷量Q等于C乘以V，储存能量U等于C乘以V平方除以2均会上升。
The source supplies energy, and moving the dielectric can involve mechanical work; compare the stated electrical energy quantity rather than assuming the capacitor alone is an isolated system.
电源提供能量，且移动电介质可能涉及机械功；应比较所陈述的电能量数值，而非假设电容器本身是孤立系统。
At a material interface, n dot D sub 2 minus D sub 1 equals sigma sub free, whereas static tangential E is continuous.
在材料界面处，法向矢量n点乘D下标2减D下标1等于sigma下标free，而静态切向电场E连续。
Normal E generally changes when permittivity changes.
当介电常数变化时，法向电场E通常也会改变。
Magnetisation M is magnetic dipole moment per unit volume, measured in A slash m.
磁化强度 M 是单位体积内的磁偶极矩，单位为安培每米。
In SI, B equals mu naught times H plus M.
在 SI 制中，B 等于 mu naught 乘以 H 加 M。
For a linear isotropic response, M equals chi sub m times H, and B equals mu naught times 1 plus chi sub m, times H.
对于线性各向同性响应，M 等于 chi sub m 乘以 H，且 B 等于 mu naught 乘以 1 加 chi sub m，再乘以 H。
B and H have different units and roles.
B 和 H 具有不同的单位和作用。
A long uniform solenoid has H approximately equal to n I when end and demagnetising effects are negligible; material response then changes B.
当端部和退磁效应可忽略时，长而均匀螺线管中的 H 约等于 n I；此时材料响应会改变 B。
Free surface current sets n cross H sub 2 minus H sub 1 equals K sub free, and normal B remains continuous.
自由面电流满足 n 叉乘 H sub 2 减 H sub 1 等于 K sub free，且法向 B 保持连续。
Ferromagnetic hysteresis and saturation cannot be represented by one constant chi sub m over every field.
铁磁滞回与饱和现象无法用一个常数 chi sub m 在所有场强下表示。
Disconnect the capacitor, then insert a dielectric of relative permittivity 4.
先断开电容器，再插入相对介电常数为 4 的电介质。
The free charge stays fixed and the capacitance becomes 4 C, so the voltage falls to V over 4 and the stored energy to U over 4.
自由电荷保持不变，电容变为 4C，所以电压降到 V 的四分之一，储存的能量降到 U 的四分之一。
With an ideal battery still connected, the voltage is fixed instead: the charge rises to 4 Q and the stored energy to 4 U.
如果理想电池仍然连接，电压就保持不变：电荷升到 4Q，储存的能量升到 4U。
The source supplies that energy, so this is a different experiment.
这部分能量由电源提供，因此这是一个不同的实验。
A slab fills half the thickness of a parallel-plate capacitor and has permittivity three epsilon naught.
一块介质板占据了平行板电容器一半的厚度，其介电常数为三倍的ε₀。
The remaining thickness is vacuum.
剩余厚度为真空。
Find C relative to the empty capacitor, and the two normal fields at fixed free charge Q.
求电容C相对于空电容器的比值，以及在固定自由电荷Q下的两个法向电场强度。
Ignore edge effects.
忽略边缘效应。
Layers are in series.
各层串联。
With no free interface charge, D equals Q divided by A is common.
若无自由界面电荷，D等于Q除以A为公共值。
E sub vac equals Q divided by epsilon naught times A, and E sub d equals Q divided by 3 epsilon naught times A.
E下标vac等于Q除以epsilon naught乘以A，E下标d等于Q除以3 epsilon naught乘以A。
V equals d over 2, times the sum of E sub vac plus E sub d, which equals 2 Q d divided by 3 epsilon naught A.
V等于d除以2，乘以E下标vac加E下标d之和，即2 Q d除以3 epsilon naught A。
Hence C equals 3 epsilon naught A divided by 2 d, which equals 3 C sub 0 divided by 2.
因此C等于3 epsilon naught A除以2 d，即3 C下标0除以2。
Award common D, each field, voltage sum and capacitance.
给分点包括：相同的D、各个电场、电压之和及电容。
Normal E is discontinuous; D is continuous.
法向E不连续；D连续。
Use free charge in the D equation and total charge in the E equation.
在D方程中使用自由电荷，在E方程中使用总电荷。
Do not confuse fixed Q with fixed V, or identify B numerically with H.
不要混淆固定Q与固定V，也不要将B的数值等同于H。
electric polarisation: Electric dipole moment per unit volume, P, contributing bound charge.
电极化强度P是单位体积内的电偶极矩，贡献束缚电荷。
magnetisation: Magnetic dipole moment per unit volume, M, entering B=μ₀(H+M).
磁化强度M是单位体积内的磁偶极矩，出现在公式B等于μ₀乘以H加M中。
Retrieve the meanings without reading the definitions, then change a parameter in the original transfer and test the limiting case.
在不阅读定义的情况下回忆这些术语的含义，然后改变原始传递中的一个参数，并检验极限情况。