# Potential Difference and Voltage

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#1
I do btec level 2 engineering course and I'm learning electronics currently. I don't think it makes sense that I don't completely understand all the basics to electricity

I get that current is literally electrons moving and resistance is just limiting the movement of those electrons. those two things are easy to understand because they can be easily visualised as they are also used to describe things that don't only exist in the studies of electricity and electronics.

But when it comes to voltage, i can never grasp the concept well enough to confidently explain it to someone else. i would like to think the potential difference is the build-up of opposite charges, separated. But i always come across multiple definitions for potential difference.
1. potential difference is the difference in electrical potential between two points.
2. potential difference is one-joule per coulomb .

Then different concept such as electrical potential, electrical potential energy, electromotive force and electric field come into the mix. i've also been told that voltage is what pushes the current, and i'm all good with that. But then why is it also called potential difference .

man, im so confused that im not entirely sure what im confused on.
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1 year ago
#2
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1 year ago
#3
Potential and potential difference are really hard concepts - and there's lots of debate among teachers about how it all actually works.
A level that works for me is:
electric potential - not a very useful term. Only really used if you connect something to 'earth', so that has a zero potential. Can be useful when you have two places with the same potential, but that's because the useful term is:
potential difference - that's what will drive a current. You need a difference in potential for a current to flow. If you stand on a high voltage wire at 400 000V that's fine - both legs at same potential, zero p.d. (take care getting on / off the wire though!)
electromotive force - emf - is an historic term, although correct to use. It just means the something (eg battery) is supplying a pd = emf.
electric field - is what actually transfers energy around a circuit (which is why lights turn on instantly) but I doubt you need to know any more about it.
So when you build a complex circuit and measure voltage, you put the probes either side of the component, so you measure the potential difference across it. You can then use V = I R to calculate the current, etc.
A Physicist might say you'd looked at the joules every coulomb of electrons arriving at the component compares with the joules every coulomb of leaving electrons, so p.d. is the amount of joules a coulomb has lost passing through the device, hence your definition which should be "1 volt = 1 J/C"
I hope that helps
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#4
(Original post by old_teach)
Potential and potential difference are really hard concepts - and there's lots of debate among teachers about how it all actually works.
A level that works for me is:
electric potential - not a very useful term. Only really used if you connect something to 'earth', so that has a zero potential. Can be useful when you have two places with the same potential, but that's because the useful term is:
potential difference - that's what will drive a current. You need a difference in potential for a current to flow. If you stand on a high voltage wire at 400 000V that's fine - both legs at same potential, zero p.d. (take care getting on / off the wire though!)
electromotive force - emf - is an historic term, although correct to use. It just means the something (eg battery) is supplying a pd = emf.
electric field - is what actually transfers energy around a circuit (which is why lights turn on instantly) but I doubt you need to know any more about it.
So when you build a complex circuit and measure voltage, you put the probes either side of the component, so you measure the potential difference across it. You can then use V = I R to calculate the current, etc.
A Physicist might say you'd looked at the joules every coulomb of electrons arriving at the component compares with the joules every coulomb of leaving electrons, so p.d. is the amount of joules a coulomb has lost passing through the device, hence your definition which should be "1 volt = 1 J/C"
I hope that helps
So, potential is stored energy, you need two different amounts of stored energy, so work can be done via the current. and that amount of work done is 1 joule per coulomb, so am i right saying(if there is no resistance) 6 coulombs =6 joules or 5 amps = 6 joules. Also, i saw a description of electric fields and i feel like it's just a diagram of how electrostatic forces interact
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1 year ago
#5
"work done is 1 joule per coulomb" - sorry, no. work done is measured in joules.
" 6 coulombs =6 joules or 5 amps = 6 joules" - again no, coulombs are the units of charge, amps for current.
These things can be related by equations, eg potential = energy / charge, charge = current x time, etc.
"electric fields and i feel like it's just a diagram of how electrostatic forces interact" is fine, you can also have 'electric field stength' which equals force / charge.
"potential is stored energy, you need two different amounts of stored energy, so work can be done via the current" - I really like that description!
I've not taught btec engineering, so I don't know the level of knowledge you need with pd. I'd imagine predicting voltages in circuits (shared in series, potential dividers, do you still do transistors?) and a feeling that it's related to the electrons' energy (which helps explain why pd is shared in series circuits) would see you fine.
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#6
I meant 6 amps btw.

(Original post by old_teach)
"work done is 1 joule per coulomb" - sorry, no. work done is measured in joules.
" 6 coulombs =6 joules or 5 amps = 6 joules" - again no, coulombs are the units of charge, amps for current.
These things can be related by equations, eg potential = energy / charge, charge = current x time, etc.
"electric fields and i feel like it's just a diagram of how electrostatic forces interact" is fine, you can also have 'electric field stength' which equals force / charge.
"potential is stored energy, you need two different amounts of stored energy, so work can be done via the current" - I really like that description!
I've not taught btec engineering, so I don't know the level of knowledge you need with pd. I'd imagine predicting voltages in circuits (shared in series, potential dividers, do you still do transistors?) and a feeling that it's related to the electrons' energy (which helps explain why pd is shared in series circuits) would see you fine.
" 6 coulombs =6 joules or 5 amps = 6 joules" - again no, coulombs are the units of charge, amps for current. - I meant 6 amps btw
"do you still do transistors?" - Yes Bi polar, and FET
AND Thank you
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1 year ago
#7
Potential difference is the pushing force... voltage is measurement compared to Earth. Is a bit like mass and weight.
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#8
(Original post by Vinny C)
Potential difference is the pushing force... voltage is measurement compared to Earth. Is a bit like mass and weight.
wdym compared to earth?
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1 year ago
#9
(Original post by Confidential_)
wdym compared to earth?
Earth... the planet essentially... is considered electrically neutral. It is so vast.
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