Your first lab. ~90 min. Measure voltage, current, and resistance with the multimeter; verify Ohm's law on a real circuit.
Goal: become fluent with the multimeter's voltage, current, and resistance modes; verify Ohm's law on a simple LED + resistor circuit.
Estimated time: 90 minutes
Prerequisites: kit unboxed; multimeter and battery accessible
Steps
Step 1: Identify the multimeter probes (5 min)
The multimeter has two probes (black and red). Plug black into "COM"; plug red into "VΩmA" (voltage / resistance / current-milliamp). Most multimeters have a separate "10A" socket for high-current measurements; you will not use it in HW-101
Step 2: Measure the 9V battery voltage (15 min)
Turn the multimeter dial to "20 V DC" (or "DCV 20" or just "V" if auto-ranging). Touch the red probe to the battery's + terminal and black to the - terminal. The display shows the battery voltage (typically 8.5-9.5 V for a fresh 9 V; lower if used). Write the reading in your notebook. Reverse the probes; note that the reading inverts (negative). This polarity matters
Step 3: Measure resistor values (20 min)
Pick three different resistors from the kit. Read the color bands; predict each resistor's value. Set the multimeter to "20k Ω" (or auto-range Ω). Touch the probes to the two leads of each resistor. Compare measured to predicted. Note tolerances: most resistors are ±5%, so 1 kΩ might read 950-1050. Tabulate
Step 4: Build a simple LED circuit (20 min)
On the breadboard: connect the 9V battery (+) through a 470 Ω resistor through an LED (anode = longer lead) to ground. The LED lights. If not: check polarity of LED; check resistor value (don't use anything below 220 Ω for safety); check battery is good
Step 5: Measure voltage and current in the circuit (20 min)
With the circuit running: set the meter to DC voltage. Measure voltage across the resistor; record. Measure voltage across the LED; record. The two should add up to ~9V (battery voltage)
For current: set the meter to "20 mA" (or DC milliamps). Break the circuit at any point; insert the meter in series (red probe on the side of the break closer to +; black probe on the other side). The current is typically 10-15 mA for this resistor + LED combo. Record
Step 6: Verify Ohm's law (10 min)
V across the resistor / R = predicted current. Compare to measured current. They should match within a few percent (mostly bounded by resistor tolerance and meter accuracy)
Expected output
- Tabulated values: battery voltage; three resistor values (predicted vs measured); voltage across resistor and LED in your circuit; current in your circuit; predicted vs measured current
Common pitfalls
- Measuring current without breaking the circuit: putting the ammeter in parallel with the resistor will short the resistor and likely blow the meter's internal fuse. Always break the circuit and insert the meter in series for current measurements
- Wrong range selection: starting on a too-small range (e.g., 200 mV when measuring 9 V) gives a "1." display (overrange). Start on a larger range and step down
Stretch (optional)
- Predict the current if you replace the 470 Ω resistor with a 1 kΩ. Build it. Measure. Compare
- Measure the LED's forward voltage with a different supply (5 V from a USB power bank). Notice the voltage is approximately the same (~2 V for red); only the resistor's voltage drop changes
Lab 1.1 v0.1. The first lab. The multimeter is your most-used tool for the whole course.