Christian

Voltage is always a difference between two points. It is not absolute - it depends on where you measure from.

When we measure voltage, we always choose a reference point (often called ground or 0 V).

If a point has more electric potential than the reference → voltage is positive

If a point has less electric potential than the reference → voltage is negative

So, a voltage is “negative” only because of the chosen reference point.

Example

Imagine a battery:

• the positive terminal is higher potential
• the negative terminal is lower potential

If you measure like this:

• Red probe on +, black on − → +9 V
• Red probe on −, black on + → −9 V

Same battery, different reference → different sign!

• Voltage is always relative
• Negative voltage means: “This point is lower than the reference point”
• The same physical voltage can appear positive or negative, depending on how you measure it