# Explain Voltage

I am trying very hard to understand voltage. I am a second year engineering student in a physics II class. I am having trouble grasping the concept of voltage. Could you guys please help me out with a few questions.

1. Please correct me if I am wrong, but isn't voltage the difference of two separate electric potentials?

2. If you were to measure the electric potential at a certain point, you'd get a certain value "x" in J/C... but what is that measuring? What does that scalar represent? If you were to put a one coulomb charge at that point you'd have "x" J. But since you only measured one point in space, what is that in reference to? It takes "x" amount of Joules to do what? Is it just saying that at that point, that charge would have that much potential energy?

3. I am also confused about voltage drop across a resistor. So if you were to hook up one lead of a voltmeter on one side of the resistor in a circuit and the other lead to the other side, and you get a reading of "x" volts. That voltage to my knowledge represents the difference between the electric potential on one side and the electric potential on the other side... the drop. So my question is if you were to just have a wire going from the positive terminal of the battery to the negative terminal of the battery, and then you measured the voltage across that, wouldn't it be zero? If not, why wouldn't the reading be zero, there is nothing in the circuit to drop the voltage, so it should remain the same and x volts minus x volts is zero.

4. But here's where I'm confused, I've seen videos of people measuring the voltage of the battery by connecting the voltmeter to each terminal of the battery and getting the reading, but why did they get a value and not zero, since the difference should be zero?

5. Also, why have I heard of voltage being "the force" that pushing electrons through a circuit, when voltage is not a force. Force is measured in Newtons, and voltage is Joules/Coulomb. So I can't grasp how voltage could "push" electrons, given the units voltage has.

6. And the last thing I don't understand is why the voltage drop across all the resistors in a circuit must always be zero. The idea that the voltage drops to zero across a 10 ohm resistor in one circuit, and also drops to zero across 2 different 10 ohm resistors in a different circuit is mind boggling to me.

I know this is a lot of questions, and the questions may be confusing, but it is hard for me to word questions when I don't know what I'm talking about.

## 2 Answers

1. Sounds about right
2. Voltage describes an electric interaction that applies a kinetic force to charge carriers (it moves them).
3. You would create a short circuit. In a very small amount of time the voltage across the wire would change from the battery voltage to zero. (It is not adviseable to do this in practice).
4. Voltmeters typically have very high internal resistance specifically so that they do not alter the circuit they are measuring.
5. Voltage is energy per unit charge stored in an electric field due to the charges' proximity. This energy is translated to kinetic energy when electric repulsion/attraction makes the charge carrier move (i.e. when current flows).
6. In general terms the voltage across a resistor in a circuit that has a non-zero voltage source in it will be non zero (it will not be zero). Possibly you are misinformed on this point, should check the source.

Let me give that a try.

1. Voltage is potential. Consider them synonyms.
2. A coulomb is the number (a collection) of electrons ( the number of electrons which flow pass a given point at a given time (1 Amp for 1 second). You can have a coulomb available at a given point, because you are just talking about the number of electrons. A coulomb is not ‘x’ Joules. A Joule is a measure of energy (heat, watts per second) equal to one amp through 1 ohm for 1 second. If a Coulomb is an Amp-second, and a Joule is a Watt-second then a Volt is a Watt-second/ a Amp Second (which =) a watt/amp.
3. The shorted battery will not produce zero volts in the real world. It will heat the wire and heat the battery. A wire is not zero ohms. Also do not forget: All batteries have a sizeable amount of internal resistance ( especially compared to a short length of wire) . It is wise to always think of any battery as a perfect battery with a resistor in series with it. That internal resistance is where most of the voltage is dropped with a small enough external resistance.
4. The meter is not zero ohms, or anything near it. A perfect meter draws no current. To the battery, the meter is not even there. It is just looking at the potential the battery has to do work.
5. A force is what can potentially to do work. So if you see 1 kilogram accelerating at 1 meter per second, every second, you know a force of one Newton is being applied. That force of one Newton can be applied to a brick wall or coiled up in the spring of a toy gun, but nothing is moving (unless something changes. With electricity you can detect that potential to “push” with a voltmeter.
6. You say “The voltage drop across all the resistors is a circuit must always equal zero” ,this is not correct. The sum of all the voltage drop across all the resistors is a circuit must always equal the value of the applied voltage. Or if you like: The Applies Voltage- the sum of the voltage drops = Zero.