The output voltage of a capacitor can be calculated using the equation V = Q/C, where V is the output voltage, Q is the charge stored on the capacitor, and C is the capacitance of the capacitor. In the video, the demonstrator is using a capacitor with a capacitance of 2.7 Farads and a charge of 1 Coulomb, which results in an output voltage of approximately 0.37 Volts (1/2.7 = 0.37).
It is important to note that this formula assumes an ideal capacitor and does not take into account factors such as resistance and leakage, which can affect the actual output voltage. To accurately measure the output voltage of a capacitor, a voltmeter can be connected to the ends of the capacitor. However, it is recommended to use a high-quality meter with a high input impedance to minimize any potential errors in the measurement. Additionally, it is important to discharge the capacitor before taking a voltage measurement to avoid any potential safety hazards.