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Lecture 4: Ohm's Law & Kirchhoff's Laws

ENGG 1500 — Intro to Electric Circuits — generated from the sample slides below.

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Ohm's law relates voltage, current and resistance: V = IR. A resistor of 1 kΩ carrying 5 mA drops 5 V.
Power dissipated by a resistor is P = VI = I²R = V²/R.
Kirchhoff's Current Law (KCL): the algebraic sum of currents entering a node is zero — charge is conserved.
Kirchhoff's Voltage Law (KVL): the algebraic sum of voltages around any closed loop is zero — energy is conserved.
Resistors in series add: R_eq = R1 + R2 + …. Resistors in parallel: 1/R_eq = 1/R1 + 1/R2 + ….
A voltage divider produces V_out = V_in · R2 / (R1 + R2). A current divider splits current inversely to resistance.

1. A 2 kΩ resistor carries 3 mA. What is the voltage across it?

2. Three currents enter a node: 2 A, 3 A and −1 A. What current leaves?

3. A 12 V source feeds R1 = 4 Ω and R2 = 8 Ω in series. Voltage across R2?

4. A 10 Ω resistor has 2 A through it. Power dissipated?

5. Two 10 Ω resistors in parallel have an equivalent resistance of:

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