brandon.horn
brandon.horn 2d ago • 0 views

Printable practice problems: Deriving the series RLC circuit differential equation.

Hey everyone! 👋 I'm trying to wrap my head around deriving the differential equation for series RLC circuits. It's kinda confusing! Anyone have a good practice sheet to help me out? 🤔
🧮 Mathematics
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christina.hanna Jan 7, 2026

📚 Topic Summary

An RLC circuit, consisting of a resistor (R), an inductor (L), and a capacitor (C) connected in series, exhibits fascinating behavior due to the interplay of these components. The differential equation that describes this circuit arises from Kirchhoff's Voltage Law (KVL), which states that the sum of the voltage drops across each element must equal the source voltage. By applying KVL and using the constitutive relationships for each component (Ohm's Law for the resistor, Faraday's Law for the inductor, and the capacitor equation), we can derive a second-order linear differential equation that governs the circuit's behavior. Solving this equation allows us to understand how the current and voltage in the circuit change over time, revealing phenomena such as oscillations and damping.

The derivation involves expressing the voltage across each component in terms of the current $i(t)$ and its derivatives. For the resistor, $v_R(t) = Ri(t)$. For the inductor, $v_L(t) = L\frac{di(t)}{dt}$. For the capacitor, $v_C(t) = \frac{1}{C}\int i(t) dt$. Applying KVL, we sum these voltages and set them equal to the source voltage $v(t)$, resulting in an integro-differential equation. Differentiating this equation with respect to time eliminates the integral term, yielding the desired second-order differential equation.

🧮 Part A: Vocabulary

Match the terms with their definitions:

Term Definition
1. Inductor A. The opposition to the flow of alternating current.
2. Capacitor B. A passive two-terminal electrical component that stores energy in an electric field.
3. Impedance C. A passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it.
4. Resistance D. A measure of the opposition to current flow in an electrical circuit.
5. Kirchhoff's Voltage Law (KVL) E. The sum of the voltage drops around any closed loop in a circuit must equal zero.

✍️ Part B: Fill in the Blanks

An RLC circuit consists of a ________, an ________, and a ________ connected in series. The differential equation is derived using ________ Voltage Law. The voltage across the inductor is proportional to the ________ of the current, while the voltage across the capacitor is related to the ________ of the current.

🤔 Part C: Critical Thinking

Explain how the damping factor in the RLC circuit differential equation affects the circuit's response to a step input. What happens when the damping factor is zero, positive, and negative?

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