RC time constant refers to the voltage curve from charging or discharging a capacitor through a resistor. The voltage shoots up quickly at first (2/3 of the voltage change) and the slowly rises to the final voltage, creating a distinct curve when graphed. It takes about 4 times as long as the initial 2/3 charge to reach 99.9% of the final voltage. So we say a capacitor is fully charged through a resistor after 5 time constants.

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## Basic properties

- Capacitor voltage changes based on how much current is flowing in or out of them and their capacitance. Voltage rises as current goes in (charges), and voltage falls as current leaves (discharges). This is actually due to an imbalance of charges on 2 separated conductive “plates”. More imbalance = more voltage across them.
- A higher voltage difference across a resistor means that more current passes through it. The voltage across an RC resistor depends on the supply voltage (final voltage) and the capacitor voltage. As the capacitor charges, there is less voltage difference across the resistor, and thus, less current flows.
- Charging/discharging a capacitor through a resistor means that the voltage will change rapidly at first and very slowly when it is close to the final voltage.
- One time constant can be calculated by multiplying the capacitor’s capacitance in Farads by the resistors resistance in Ohms. Remember to convert, millifarads (mF), microfarads (µF), nanofards (nF), picofarads (pF), to farads before making the calculation.
- One time constant is how long it takes to change/discharge approx. 2/3 of the remaining voltage difference.

### Video

Electronics course 5 capacitor component RC time constant circuit fragment tutorial

#### Video diagram

Wide range of values. I mostly use this kit. I use a few values that I got from other kits. As an Amazon Associate I earn from qualifying purchases.

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