# What does it mean when a circuit has two voltages?

In summary, the conversation discusses interpreting a circuit with a negative voltage, the use of negative voltages, and the values for a circuit with multiple voltage sources. It is explained that voltages are relative measurements and can be any value depending on the circuit elements and sources. Negative voltages are used to calculate the potential difference and can be helpful in detecting circuit issues. The use of a ground or reference potential at 0 volts is also mentioned.
(Sorry for the bad title wording.)

I attached a picture of what I mean. Those are two points, each attached to a different voltage source. I'm used to seeing something like +9 [V] to 0 [V].

1) How am I supposed to interpret a circuit with a -X [V], where X = any positive integer, at the end?

2) Why would you use the negative in the first place?

3) Could the values for the circuit be +9 to -3, or does it have to be symmetric like +9 to -9?

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• circuit.jpg
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Voltages are only a relative measurement You can't say something is 9V unless you say 9V measured against something - you can only talk about a voltage difference across a component.
Normally if there is only a single voltage you assume the other side is at 0v and this is the potential of Earth.
You can calculate anything in this circuit by working out the voltage difference, having +9V on one side of a component and -9V on the other is exactly the same as having +18V on one side and 0 on the other, or +12V and -6V.

Think of it like a problem in mechanics, it doesn't matter what you call 0 height, everythign else works out the same.

If your diagram is symmetric, for simplicity, think of a ground attached to both vertical portions of the circuit at the center...say a ground connection in the middle of each.

Those voltages could have any values depending on the circuit elements and voltage or current sources. A mix of voltage and current sources, together with different circuit elements, can also cause different sign voltages...

Last edited:
(Sorry for the bad title wording.)

I attached a picture of what I mean. Those are two points, each attached to a different voltage source. I'm used to seeing something like +9 [V] to 0 [V].

1) How am I supposed to interpret a circuit with a -X [V], where X = any positive integer, at the end?

2) Why would you use the negative in the first place?

3) Could the values for the circuit be +9 to -3, or does it have to be symmetric like +9 to -9?

1) Interpret it as a negative voltage. So in your picture, the voltage across the device would be 9 V - (-9 V) = 18 volts. Calculate accordingly.

2) 0 Volts is usually taken as "ground". It is just a reference potential. Some voltages are below it, some above.

3) Yes, it can be +9 V to -3 V, and it need not be symmetric. It just needs to be what it is.

As an actual example, HP mini computers of the 1970's used +5 and -2 volts for their TTL logic. Switching rates were a bit faster due to the extra 2 volts, and short to ground (0 volts) or breaks in circuits could be detected more easily.

+9v and -9v is just the mentioning the electric potential difference. In that circuit the potential difference is 18V. It can be -3 or whatever you like it. It's just taking relative to the neutral or ground which is taken as 0V.

## 1. What is the definition of voltage in a circuit?

Voltage in a circuit is the measure of electrical potential energy difference between two points. It is measured in volts (V) and is responsible for the movement of electrons through the circuit.

## 2. How can a circuit have two voltages?

A circuit can have two voltages when it is connected to multiple power sources, such as a battery and a generator. Each power source can provide a different voltage to the circuit.

## 3. What happens when a circuit has two voltages?

When a circuit has two voltages, the total voltage in the circuit is the sum of the individual voltages. This means that the electrons in the circuit will experience a stronger force and therefore move with more energy.

## 4. Can a circuit have two voltages of the same magnitude?

Yes, a circuit can have two voltages of the same magnitude, but they must be in opposite directions. This is known as a balanced circuit and is commonly used in electronic devices to cancel out unwanted noise.

## 5. How do you measure the voltage in a circuit with two voltages?

To measure the voltage in a circuit with two voltages, you can use a voltmeter. It will show the total voltage in the circuit, which is the sum of the individual voltages. Alternatively, you can use Ohm's Law (V = IR) to calculate the voltage if you know the current and resistance in the circuit.

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