A6 Capacitors and Inductors

Updated 4 Oct 2026

เราจะเรียนทั้งหมด 3 ตัว ก็คือ R, C, L
- R → Absorbed
- C, L → Energy Stored Elements (ไม่กินพลังงาน)
วงจรที่เราเรียนจะมีทั้งหมด 2 รูปแบบ
1. Energy stored elements 1 ตัว (L หรือ C) + R 1 ตัว → First-Order
2. Energy stored elements 2 ตัว (L และ C) + R 1 ตัว → Second-Order
Electric Circuits that do not contain capacitors or inductors are represented by algebraic equations

$\begin{aligned} 8i_1-3i_2=6 \\ -3i_1+5i_2=0 \end{aligned}$
— but contain capacitors and/or inductors are represented by differential equations (ธรรมชาติของ L กับ C มันจะอธิบายด้วย Differential equations)

$\frac{d_{i_L}}{dt}+10i_l=0$

Capacitors

Basic Properties

A capacitor is a passive element designed to store energy in its electric field. When a voltage source is connected to the capacitor, the source deposits a positive chargeq on one plate and a negative charge on the other.

An inductor is a passive element designed to store energy in its magnetic field. It consists of a coil of conducting wire.

\boxed{v(t)=L\frac{di(t)}{dt}}

\boxed{i=\frac{1}{L}\int_{t_0}^t v(t)dt+i(t_0)}

\boxed{p=iv=i\Big(L\frac{di(t)}{dt}\Big)}

w=\int_{-\infty}^t p dt=\frac{1}{2}Li^2