Why Does a Voltmeter Show Negative Voltage?

[fisico30]

Hello Forum,

maybe not a new topic but let me ask anyway.
The voltmeter is a simple device used to measure voltage or potential difference. Take a 9 Volt battery. If we connect it to a voltmeter the reading could be either +9 V or - 9 V. What makes one of the leads of voltmeter different from the other one such that the voltage reading can be negative? Current is actually electrons flowing from low to high potential

At times I am still confused about the concept of negative voltage. Given a circuit, we can choose any point and make it the reference point. That means that the voltage at that point can be called zero even if we don't connect that point with Earth ground, correct? Other points in the circuit can be at a positive or negative voltage. Is that all there is to say about negative voltage? We could get by without negative voltage by properly choosing the zero point potential. Why don't we do that?

thanks!

 

[russ_watters]

Given a circuit, we can choose any point and make it the reference point. That means that the voltage at that point can be called zero even if we don't connect that point with Earth ground, correct? Other points in the circuit can be at a positive or negative voltage. Is that all there is to say about negative voltage?

Yes.

We could get by without negative voltage by properly choosing the zero point potential. Why don't we do that?

How would we do that and what benefit would there be? I suppose a digital multimeter could be made to give an error message instead of a negative voltage reading, but that would just make it less useful.

 

[sophiecentaur]

If you were to build a house on top of a mountain, which would be better
1. Specify the heights of the floors and basement as heights above sea level.
2. Take the ground floor as zero and have positive heights to the upper stories and a negative height for the basement/
?
That is your question, re-stated in terms of gravitational potential rather than electric potential. Does that not show that Negative Voltages are useful?