TheAlgorithms/Python · error · ValueError

Capacitance must be positive.

Error message

Capacitance must be positive.

What it means

Thrown by charging_capacitor() when capacitance <= 0. Capacitance scales the RC time constant; zero or negative capacitance is non-physical for a charging model, so the library refuses it (this is the last of the three sequential guards).

Source

Thrown at electronics/charging_capacitor.py:65

    ValueError: Source voltage must be positive.

    >>> charging_capacitor(source_voltage=20,resistance=-2000,capacitance=30,time_sec=4)
    Traceback (most recent call last):
        ...
    ValueError: Resistance must be positive.

    >>> charging_capacitor(source_voltage=30,resistance=1500,capacitance=0,time_sec=4)
    Traceback (most recent call last):
        ...
    ValueError: Capacitance must be positive.
    """

    if source_voltage <= 0:
        raise ValueError("Source voltage must be positive.")
    if resistance <= 0:
        raise ValueError("Resistance must be positive.")
    if capacitance <= 0:
        raise ValueError("Capacitance must be positive.")
    return round(source_voltage * (1 - exp(-time_sec / (resistance * capacitance))), 3)


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass capacitance in farads as a positive number (e.g. 30 as in the doctest, or 1e-6 for 1 uF).
2. Validate unit conversion before the call; ensure floats, not truncated ints.
3. Confirm the earlier guards passed — this error implies source_voltage and resistance were already positive.

Example fix

# before
charging_capacitor(source_voltage=30, resistance=1500, capacitance=0, time_sec=4)

# after
charging_capacitor(source_voltage=30, resistance=1500, capacitance=4.7e-6, time_sec=4)

if capacitance <= 0:
    raise ValueError("capacitance must be positive farads")
v = charging_capacitor(source_voltage, resistance, capacitance, time_sec)

When it happens

Trigger: charging_capacitor(source_voltage=30, resistance=1500, capacitance=0, time_sec=4) or any negative capacitance value.

Common situations: Unit errors (pF/nF/uF vs F) producing 0 after integer truncation; unset config defaults of 0; passing a component count instead of a farad value.

Related errors

• Source voltage must be positive.
• Resistance must be positive.
• Inductance must be positive.
• Capacitor at index {index} has a negative or zero value!
• You cannot supply more or less than 2 values

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/66c155154bd8f5a5. Report an issue: GitHub.