Lesson 9: Electricity & Circuits
Electric circuits are the backbone of every electronic device. Understanding voltage, current, resistance, and how components connect in series and parallel is essential for engineering, computer science, and everyday technology.
Key Concepts
Voltage, Current, Resistance
Voltage (V, volts) is the electric potential difference — the 'push'. Current (I, amperes) is the flow of charge. Resistance (R, ohms Ω) opposes current flow. Ohm's Law: V = IR.
Series Circuits
Components connected end-to-end in a single loop. Same current flows through all. Voltages add. Total resistance = R₁ + R₂ + R₃ + ... If one component fails, the whole circuit breaks.
Parallel Circuits
Components connected across the same two nodes. Same voltage across all. Currents add. 1/R_total = 1/R₁ + 1/R₂ + ... If one component fails, others keep working. (Why homes are wired in parallel.)
Power in Circuits
P = IV = I²R = V²/R. Measured in watts. A 60W bulb at 120V draws I = P/V = 0.5 amps. Appliances rated for higher wattage draw more current.
Kirchhoff's Laws
KVL: The sum of all voltages around any closed loop = 0. KCL: The sum of currents into any node = sum out. These laws are the foundation for analyzing any circuit.
🔬 Virtual Lab: Series vs. Parallel Circuit Builder
Add resistors to the series or parallel circuit. Watch resistance, current, and power update live. Compare the two configurations.
✅ Check Your Understanding
1. Ohm's Law states that V = :
2. In a parallel circuit, if one bulb burns out:
3. Total resistance in a series circuit with R₁=100Ω and R₂=150Ω is: