The three quantities every electrical circuit obeys. By the end of the week you can describe each in plain English, measure each with a multimeter, and predict each in a simple circuit using Ohm's law.
Reading (~30-45 min)
- Horowitz and Hill, The Art of Electronics, Ch 1 §1.1 (introduction to voltage, current, and resistance). Read carefully; this is the cleanest plain-English account of the three quantities in print
- The Arduino R4 Classroom Pack quick-start card; the multimeter quick-start card
Lecture (~1.5 hr)
- The water-pipe analogy. Voltage is the pressure difference; current is the flow rate; resistance is how narrow the pipe is. The analogy is imperfect (electricity is not water) but useful for first intuition
- Ohm's law: V = I × R. Three variables; given any two, you can find the third
- Power: P = V × I. Why over-current resistors get hot; the smell of an over-driven part
- Safety: at HW-101 voltages (≤ 9V battery; or USB-powered Arduino at 5V) you cannot shock yourself dangerously. You CAN damage parts through wrong wiring; a shorted battery or wrong-polarity LED is the most common failure mode. The course's first safety rule: when in doubt, measure before you connect
Lab exercises (~2 hr)
Lab 1.1: Multimeter Basics. Measure voltage on a 9V battery; measure resistance on three different resistors; measure current through a simple LED circuit. ~90 minutes.
Independent practice (~3 hr)
- Predict and measure five more resistor values using the color code (see the printable color-code card in your kit). Verify with the multimeter
- Build the kit's first sample circuit (LED + resistor + battery) without instructions. Photograph it. Annotate your photograph with voltage and current measurements at every node
- Read the resistor color-code Wikipedia article. Notice that the code is the same in every country and has been for ~60 years; once you learn it, you have it for life
Reflection prompts
- The water-pipe analogy made voltage feel like pressure. Where does the analogy break down? Name one phenomenon water cannot model
- The multimeter measures three different quantities through one set of probes. What does the meter do internally to switch between modes? You do not have to know the answer; the question is the point
- You measured current by breaking the circuit and inserting the meter in series. Why is that necessary? What would happen if you tried to measure current with the meter in parallel?
What's next
Week 2 takes Ohm's law from one resistor to combinations of resistors. Series and parallel. The voltage divider, which appears in every analog circuit you will ever read.