📚 Energy Stored in a Capacitor | 电容器储存的能量
Capacitors are passive components used in almost every electronic circuit. In CIE A-Level Physics, understanding the energy stored in a capacitor is not only about remembering a formula; it is about applying energy conservation, interpreting V-Q graphs, and linking circuit behaviour to electric fields. This article covers the required theory, derivations, experiments, applications, and common exam pitfalls.
电容器是几乎每个电子电路中都会用到的无源元件。在 CIE A-Level 物理中，理解电容器储存的能量不仅仅是记住公式，还要学会应用能量守恒、解读 V-Q 图，并把电路行为与电场联系起来。本文涵盖所需的理论、推导、实验、应用和常见考试陷阱。
1. Capacitor Energy Basics | 电容器储能基础
A capacitor is a device that stores charge Q on two conductors separated by an insulator. When a potential difference V is applied, positive charge builds up on one plate and negative charge on the other. The stored charge is proportional to the applied voltage, giving the defining equation for capacitance.
电容器是一种在两个被绝缘体隔开的导体上储存电荷 Q 的器件。当施加电势差 V 时，一块极板上积累正电荷，另一块积累负电荷。储存的电荷与外加电压成正比，由此得到电容的定义式。
Q = CV
Here C is the capacitance in farads (F), Q is the charge in coulombs (C), and V is the potential difference in volts (V). In many practical capacitors, capacitance is given in microfarads (µF) or picofarads (pF), so careful unit conversion is essential.
式中 C 是电容，单位为法拉 (F)；Q 是电荷，单位为库仑 (C)；V 是电势差，单位为伏特 (V)。在许多实际电容器中，电容以微法 (µF) 或皮法 (pF) 给出，因此单位换算是必不可少的。
Because the plates carry equal and opposite charges, an electric field exists between them. Energy is not stored in the charges themselves but in this electric field. When the capacitor discharges through a circuit, this field energy is released and converted into other forms, such as heat or light.
由于两极板带有等量异种电荷，它们之间存在电场。能量并非储存在电荷本身，而是储存在这个电场中。当电容器通过电路放电时，这部分电场能量被释放并转化为其他形式，例如热或光。
2. Work Done in Charging a Capacitor | 给电容器充电时所做的功
ds up, the voltage V increases, so later charge transfers require more work per unit charge.
为了使电容器充电，电源必须把电子从一块极板移到另一块极板。每移动少量电荷 dQ 经过电势差 V，需要做功 dW = V dQ。随着电荷积累，电压 V 增大，因此后来转移的电荷需要做更多的功。
, the total work is the integral of Q/C with respect to Q from zero to the final charge Q.
总功可以通过积分
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