Your first lab: work out how much power a resistor can safely take, learn the two modes of the Keysight E36312A power supply (constant voltage and constant current), measure a resistor’s I–V line, and find out why an LED does not obey Ohm’s law. Every panel below is a live simulation, so you can predict each reading before you take it.
A resistor turns electrical energy into heat. Our resistors are rated for ¼ W, but we derate them by a factor of 2 and never go above ⅛ W. That keeps them cool enough to touch and keeps their resistance stable. Before touching the power supply you calculate the largest current and voltage that stay under that limit.
Try the pre-lab example: 20 Ω, 5 W, derate by 2 gives Pmax = 2.5 W and Vmax = √(2.5 × 20) = 7.071 V.
Each channel of the E36312A has two settings: a voltage setpoint and a current setpoint (a limit). It obeys whichever one it hits first. While the circuit draws less than the current limit, the supply holds the voltage steady: CV, constant voltage. If holding that voltage would need more current than the limit, it holds the current at the limit instead and lets the voltage drop: CC, constant current. The display always tells you which mode you are in.
Load: the 1 Ω resistor (plus about 0.07 Ω of clip and lead resistance).
The current limit is your safety net. Set it to Imax from the pre-lab (0.354 A for 1 Ω at ⅛ W). Then no matter how far you turn the voltage knob, the resistor can never get more than ⅛ W.
Once I = V/R reaches the limit, the supply switches to CC. Turning the voltage setpoint higher changes nothing: the measured voltage stays at Ilimit × R. That is how you know the sweep is over (step 16).
Keypad: highlight the field, type .05, then press Enter; nothing changes until Enter. Knob: 1 mV per click when turned slowly, bigger jumps when turned fast (it is velocity-sensitive).
The supply reports current flowing out of its + terminal (active sign convention). The resistor uses current flowing into its + terminal (passive). Connected together they describe the same current, so Isupply = Iresistor and Vsupply = Vresistor.
You raise the voltage in 0.05 V steps, record V, I and the mode at each step, then let Google Sheets fit a straight line. The slope of the I-vs-V line is the conductance G (in siemens, S), and the resistance is its reciprocal: R = 1/G. Watch the data come in.
The supply measures voltage at its own terminals, so the alligator clips, test leads and contact points are measured as part of “the resistor”. For a 1 Ω part, 0.05–0.1 Ω of wiring is already 5–10%. Untick the box above to see the pure resistor.
The supply’s readings have small offsets and limited resolution (the last digit flickers). A tiny b like 0.001 is normal. A large b means a reading was copied wrong.
An LED is polar: current only flows easily one way, from the long lead (anode, +) to the short lead (cathode, −). Below about 2.5 V almost no current flows; above it, a tiny voltage increase makes the current shoot up. So there is no single “resistance” for an LED. Set the voltage limit to 3.3 V first, then sweep in CC mode and in CV mode.
Near its turn-on voltage, a few tens of millivolts change the LED current a lot. In CV mode a small knob turn can push far too much current. In CC mode you choose the current directly, and the 3.3 V limit stops anything silly.
From 0 to 2.5 V the LED is still below its turn-on point, so the current is microamps or less, often below what the supply can display. That is the “off” part of the curve.
Δr = ΔV/ΔI between two neighbouring points is the slope of the curve at that spot. At high current it is around 15 Ω; at low voltage ΔI is almost zero, so Δr is enormous. Same device, wildly different “resistance”: that is what non-ohmic means.
Sheets will happily fit a line, but the points bend sharply, so the line misses most of them and its slope means nothing physical. That is your answer to “does this device follow Ohm’s law?”
Attach both plots as screenshots, put everything in one PDF and upload it to Brightspace. Sign out of the lab computer when you leave.