The slow-motion capacitor
Watch a capacitor approach 5 V, then return toward zero.
Difficulty: Breadboard. Estimated build time: about 25 minutes. 4-line bill of materials. Compare supplier offers when available. Build a slow RC circuit that a voltmeter can follow.
Prepare the bench
Use an isolated, regulated 5 V source with a 20 mA current limit and a digital voltmeter with approximately 10 MΩ input resistance. These are bench tools, not included in the shopping list. Disconnect power before changing connections. Confirm breadboard rail continuity and check for supply shorts before powering up.
Wire a safe charge path
Connect the positive lead of a 100 µF, 16 V electrolytic to node VC and its negative lead to ground. Connect a 100 kΩ resistor from VC to node DRIVE. Initially connect DRIVE to ground. Measure VC in DC volts; keep capacitor polarity correct.
Charge and compare
Move only the free DRIVE connection from ground to +5 V, leaving R in series. Nominal τ is 10 s. Starting near 0 V, expect about 3.16 V after 10 s and 4.97 V after 50 s. A 10 MΩ meter and capacitor leakage slightly alter the result; ordinary electrolytic tolerance can be substantial.
Discharge through the resistor
Disconnect DRIVE from +5 V, then connect DRIVE to ground so the same resistor discharges the capacitor. From 5 V, expect about 1.84 V after 10 s. Leave the resistor connected until VC is below 0.1 V before dismantling. Never short the capacitor terminals.