What's the difference between voltage and potential difference? Watch

blobbybill
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What's the difference between voltage and potential difference?

Also, what is the difference between a resistor, a potential divider and a potentiometer? I am getting confused with these terms.
Thanks!
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uberteknik
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(Original post by blobbybill)
What's the difference between voltage and potential difference?

Also, what is the difference between a resistor, a potential divider and a potentiometer? I am getting confused with these terms.
Thanks!
Voltage

Each and every electron has the inherent property of being able to exert a force over a distance. That force is of course the electric or charge force. In other words, electrons have the 'potential' to perform work - they are a source of potential energy.

A collection of electron charge is measured in Coulombs. i.e. how many electrons available. Voltage is the ability to perform work and is defined as Energy per Coulomb of charge. i.e. Volts = Joules per Coulomb.

Voltage is therefore a measure of the combined 'electric charge force potential' exerted by a source of electrons: batteries, dynamo's, solar cells etc. i.e. it is the collective electron charge force able to be exerted by a huge collection of electrons.

Think of voltage in a similar way to water pressure. The deeper the water, the greater the pressure at the bottom of the tank. But until the water starts flowing in a pipe, that pressure is only a potential source of energy.

So it is with electrons. The voltage pressure exerted by a collection of electrons has the potential to perform useful work which can only be liberated when electrons start flowing in a circuit. Until current flows, it is only 'voltage potential'. The higher the voltage, the greater the electric charge pressure exerted on the circuit.

Potential Difference and resistors

This is a measure of the energy liberated between two points in a circuit where current flows. A resistor restricts the flow of electrons and forces them to give up energy in the form of heat.

The voltage pressure must drop across the resistor because the energy potential of electrons leaving the resistor is lower than those entering it since energy has been converted to heat in the resistor.

Hence 'potential difference' of electron pressure measured across the resistor - also measured in volts - is another way of saying how much energy was used up between the two points as measured in volts (Joules per Coulomb of charge).

Potential divider

Two resistors placed in series with a current flowing through them will create a potential difference across each resistor.

i.e. the original voltage potential is divided into two parts with a potential difference across each resistor dependent on the ratio of the two resistances.

The original source potential voltage has been divided into two parts (in proportion) dependent on the value of each resistor with both parts summing to the original voltage potential.

Potentiometer

Nothing more than a crude electro-mechanical device to create a variable potential divider or variable resistor dependent on the circuit configuration.
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blobbybill
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(Original post by uberteknik)
Voltage

Each and every electron has the inherent property of being able to exert a force over a distance. That force is of course the electric or charge force. In other words, electrons have the 'potential' to perform work - they are a source of potential energy.

A collection of electron charge is measured in Coulombs. i.e. how many electrons available. Voltage is the ability to perform work and is defined as Energy per Coulomb of charge. i.e. Volts = Joules per Coulomb.

Voltage is therefore a measure of the combined 'electric charge force potential' exerted by a source of electrons: batteries, dynamo's, solar cells etc. i.e. it is the collective electron charge force able to be exerted by a huge collection of electrons.

Think of voltage in a similar way to water pressure. The deeper the water, the greater the pressure at the bottom of the tank. But until the water starts flowing in a pipe, that pressure is only a potential source of energy.

So it is with electrons. The voltage pressure exerted by a collection of electrons has the potential to perform useful work which can only be liberated when electrons start flowing in a circuit. Until current flows, it is only 'voltage potential'. The higher the voltage, the greater the electric charge pressure exerted on the circuit.

Potential Difference and resistors

This is a measure of the energy liberated between two points in a circuit where current flows. A resistor restricts the flow of electrons and forces them to give up energy in the form of heat.

The voltage pressure must drop across the resistor because the energy potential of electrons leaving the resistor is lower than those entering it since energy has been converted to heat in the resistor.

Hence 'potential difference' of electron pressure measured across the resistor - also measured in volts - is another way of saying how much energy was used up between the two points as measured in volts (Joules per Coulomb of charge).

Potential divider

Two resistors placed in series with a current flowing through them will create a potential difference across each resistor.

i.e. the original voltage potential is divided into two parts with a potential difference across each resistor dependent on the ratio of the two resistances.

The original source potential voltage has been divided into two parts (in proportion) dependent on the value of each resistor with both parts summing to the original voltage potential.

Potentiometer

Nothing more than a crude electro-mechanical device to create a variable potential divider or variable resistor dependent on the circuit configuration.

Potential divider

Two resistors placed in series with a current flowing through them will create a potential difference across each resistor.

i.e. the original voltage potential is divided into two parts with a potential difference across each resistor dependent on the ratio of the two resistances.

The original source potential voltage has been divided into two parts (in proportion) dependent on the value of each resistor with both parts summing to the original voltage potential.
I don't get the difference between the voltage and the potential difference though. I get that a potential difference is created over two points, hence the "difference", but I don't get how voltage and potential difference are different, and in an exam, I wouldn't know whether to say potential difference or voltage.
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uberteknik
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(Original post by blobbybill)
I don't get the difference between the voltage and the potential difference though. I get that a potential difference is created over two points, hence the "difference", but I don't get how voltage and potential difference are different, and in an exam, I wouldn't know whether to say potential difference or voltage.
Think of 'voltage potential' as the source of potential energy available at that point and 'voltage potential difference' as that potential energy converted into a different form.

Rather like gravitational potential energy vs kinetic energy - both are measured in the same units.
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blobbybill
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(Original post by uberteknik)
Think of 'voltage potential' as the source of potential energy and 'voltage potential difference' as that potential energy converted into a different form.

Rather like gravitational potential energy vs kinetic energy - both are measured in the same units.
Okay, so how would I know whether voltage or potential difference is the correct term to use, and when? In which instances would I refer to it as potential difference and in which instances would I refer to it as voltage?

I really don't understand the difference (I get what you said about the source and the difference though), and I don't get in an exam which one of the two I call it as and why?

I also know the definition of potential difference which is the work done per unit charge, but I am still none the wiser as to which one to use.
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Cerdic
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Voltage is a potential difference measured in volts. It's like the difference between mileage and distance.

In reality it tends to be that engineers talk of voltage, while physicists use potential difference more.
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uberteknik
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(Original post by blobbybill)
Okay, so how would I know whether voltage or potential difference is the correct term to use, and when? In which instances would I refer to it as potential difference and in which instances would I refer to it as voltage?

I really don't understand the difference (I get what you said about the source and the difference though), and I don't get in an exam which one of the two I call it as and why?
Say you have a battery. The voltage available at the terminals is voltage potential - it's a source of energy.

Now connect two resistors to the battery terminals in series to make a circuit.

The voltage across the battery terminals is still voltage potential -it's still a source.

But now because a circuit is created, current will flow through the resistors. Each resistor will convert the original voltage potential to heat. The energy converted by each resistor is measured as a voltage potential difference when measured across each resistor independently.
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blobbybill
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(Original post by uberteknik)
Say you have a battery. The voltage available at the terminals is voltage potential - it's a source of energy.

Now connect two resistors to the battery terminals in series to make a circuit.

The voltage across the battery terminals is still voltage potential -it's still a source.

But now because a circuit is created, current will flow through the resistors. Each resistor will convert the original voltage potential to heat. The energy converted by each resistor is measured as a voltage potential difference when measured across each resistor independently.
Ok thanks, do you think it would make much of a difference in an exam if I put the wrong term, ie voltage instead of potential difference?

And would I lose marks if I wasnt sure which term to use, and I put "voltage/potential difference" as the answer, would that lose me marks?
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blobbybill
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(Original post by uberteknik)
Say you have a battery. The voltage available at the terminals is voltage potential - it's a source of energy.

Now connect two resistors to the battery terminals in series to make a circuit.

The voltage across the battery terminals is still voltage potential -it's still a source.

But now because a circuit is created, current will flow through the resistors. Each resistor will convert the original voltage potential to heat. The energy converted by each resistor is measured as a voltage potential difference when measured across each resistor independently.
And in a circuit, if it wanted the voltage total to the circuit, that would be voltage right? (because its voltage potential?)

And if it wanted the voltage in a certain point/part of a circuit, would that be voltage or potential difference?
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uberteknik
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(Original post by blobbybill)
Ok thanks, do you think it would make much of a difference in an exam if I put the wrong term, ie voltage instead of potential difference?

And would I lose marks if I wasnt sure which term to use, and I put "voltage/potential difference" as the answer, would that lose me marks?
As long as you stated the correct answer and the correct units (volts), unless the mark scheme specifically looked for the term potential difference, I doubt you would lose marks.
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uberteknik
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(Original post by blobbybill)
And in a circuit, if it wanted the voltage total to the circuit, that would be voltage right? (because its voltage potential?)

And if it wanted the voltage in a certain point/part of a circuit, would that be voltage or potential difference?
It's all about context.

If you are referring to the voltage as a source it's voltage potential.

If you are referring to the voltage as a loss, it's potential difference.
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Cerdic
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(Original post by uberteknik)
Say you have a battery. The voltage available at the terminals is voltage potential - it's a source of energy.

Now connect two resistors to the battery terminals in series to make a circuit.

The voltage across the battery terminals is still voltage potential -it's still a source.

But now because a circuit is created, current will flow through the resistors. Each resistor will convert the original voltage potential to heat. The energy converted by each resistor is measured as a voltage potential difference when measured across each resistor independently.
You're confusing things. A voltage is the difference in electrical potential between two points.

Difference in electrical potential = potential difference = voltage.

There is no such thing as a "voltage potential" and trying to complicate the matter anymore will likely confuse OP at their level.
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Cerdic
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(Original post by blobbybill)
And in a circuit, if it wanted the voltage total to the circuit, that would be voltage right? (because its voltage potential?)

And if it wanted the voltage in a certain point/part of a circuit, would that be voltage or potential difference?
You measure the voltage/ PD across points in a system, so in a battery circuit it would be from the terminals.

"The voltage across the circuit is 5V" is equivalent to "The potential difference across the circuit is 5V".

What would be a bit jarring is if you were using other units, so I probably wouldn't say (although it's not necessarily wrong) "The system has a voltage of 25nV", but I would say "The system has a potential difference of 25nV". Having said that, I can't remember any time when I've used nano volts as a unit.
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blobbybill
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(Original post by Cerdic)
You're confusing things. A voltage is the difference in electrical potential between two points.

Difference in electrical potential = potential difference = voltage.

There is no such thing as a "voltage potential" and trying to complicate the matter anymore will likely confuse OP at their level.
Okay then. Short and sweet please, make it as clear as possible and when you would use each term.
What is voltage? What is potential difference? What is the difference between voltage and potential difference? How do I know which term to use in which instance?

Thanks! I think knowing the answer to the above questions would help me a lot, I do only have a fairly basic knowledge of the terms at the moment.
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uberteknik
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(Original post by blobbybill)
Okay then. Short and sweet please, make it as clear as possible and when you would use each term.
What is voltage? What is potential difference? What is the difference between voltage and potential difference? How do I know which term to use in which instance?

Thanks! I think knowing the answer to the above questions would help me a lot, I do only have a fairly basic knowledge of the terms at the moment.
Indeed. I'd like to know the answer as well.
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Cerdic
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(Original post by blobbybill)
Okay then. Short and sweet please, make it as clear as possible and when you would use each term.
Interchangeably.

What is voltage? What is potential difference? What is the difference between voltage and potential difference? How do I know which term to use in which instance?
They are the difference in electrical potential between two points. There is no difference for all intents and purposes.

Thanks! I think knowing the answer to the above questions would help me a lot, I do only have a fairly basic knowledge of the terms at the moment.
No worries.
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blobbybill
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(Original post by Cerdic)
Interchangeably.


They are the difference in electrical potential between two points. There is no difference for all intents and purposes.


No worries.
Ok so it doesn't matter whether I use potential difference, or whether I use voltage as the term? And would it be better to use "potential difference" regardless, all the time? I hear potential difference is a more advanced term.
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Jpw1097
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(Original post by blobbybill)
What's the difference between voltage and potential difference?

Also, what is the difference between a resistor, a potential divider and a potentiometer? I am getting confused with these terms.
Thanks!
The problem with voltage is that it is such an ambiguous term that can describe potential difference and electromotive force (emf). Suppose an electron leaves the negative terminal with some electric potential energy. As it flows through a component in the circuit, such as a a resistor/thermistor, some or all of the electric potential energy of the electron is converted into other forms of energy, such as heat in this case. Therefore, the potential difference across the resistor/thermistor is the difference in electric potential energy of an electron before and after the component.
Emf refers to how much energy is given to an electron in the battery.

These are the definitions for potential difference and emf that I used in my A levels:
Potential difference in the energy transferred from electrical energy to another form of energy (e.g. heat) per unit charge.
Emf on the other hand, is the energy transferred from a source (e.g. chemical energy in a battery) to electrical energy per unit charge.
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blobbybill
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(Original post by Jpw1097)
The problem with voltage is that it is such an ambiguous term that can describe potential difference and electromotive force (emf). Suppose an electron leaves the negative terminal with some electric potential energy. As it flows through a component in the circuit, such as a a resistor/thermistor, some or all of the electric potential energy of the electron is converted into other forms of energy, such as heat in this case. Therefore, the potential difference across the resistor/thermistor is the difference in electric potential energy of an electron before and after the component.
Emf refers to how much energy is given to an electron in the battery.

These are the definitions for potential difference and emf that I used in my A levels:
Potential difference in the energy transferred from electrical energy to another form of energy (e.g. heat) per unit charge.
Emf on the other hand, is the energy transferred from a source (e.g. chemical energy in a battery) to electrical energy per unit charge.
So I should always really talk about potential difference rather than voltage when talking about the amount of volts in a part of a circuit?

And are you able to explain emf in more detail and more clearly please? I don't fully understand emf.

Thanks!
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Jpw1097
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(Original post by blobbybill)
So I should always really talk about potential difference rather than voltage when talking about the amount of volts in a part of a circuit?

And are you able to explain emf in more detail and more clearly please? I don't fully understand emf.

Thanks!
I would never use the term voltage, it doesn't really mean anything.

I'll try. Emf is basically how much energy is given to an electron by a battery. Remember that 1 volt is equal to 1 joule of energy per coloumb. The charge of an electron is 1.6 x 10-19 coulombs, hence 6.25 x 1018 electrons make up one coulomb. Therefore, 1 volt is equal to one joule of energy for every 6.25 x 1018 electrons.

So if the emf is 6V, 6 joules of energy are given for every 6.25 x 1018 electrons.
Therefore every coulomb (6.25 x 1018 electrons) leaving the battery will have 6 joules of electrical energy. Now, if these electrons flow through one resistor, they will transfer this electrical energy into other forms of energy, predominantly heat. If there is only one resistor in the circuit, the electrons will transfer all of their electrical energy into heat and other forms of energy. Hence, for every 6.25 x 1018 electrons that flow through the resistor, 6 joules of energy will be transferred into heat. Therefore, provided the battery has no internal resistance (ie, no energy is lost in the battery itself as heat) then the energy given to each electron (emf) will be the same as the energy dissipated in the circuit and across the components (potential difference).
If there are multiple components in the circuit, the energy of each electron will essentially be 'shared out' across the components. However, the sum of the potential differences across the multiple components will be the same as if there was only one component in the circuit.

If there is no internal resistance in the battery, emf = the sum of all the potential differences in the circuit.

Hopefully that helps.
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