Please help, Potential difference, Voltage?

Question

Question1:
I know the Potential difference, and Voltage aren't quite the same thing. What are the differences?

Question2:
I understand the potential difference is the change of force in the resistor, the difference of force before the resistor and after.
Example: If the source 5v supplied into the circuit, so the volt before resistor is 5 and after 4. That means the Potential difference is 1?

Question3:
Useful of knowing the potential difference in the life of electrician and engineer in general?

Thank you?

Answer 1

Q1. The word 'voltage' is commonly used with 2 slightly different meanings:

a) The potential at a single point.

b) The potential difference between 2 points.



For b), we should really call it 'voltage difference' but people usually don't bother.

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Q2 Potential difference is not really a change in force. Though when you have a potential difference you can think of it acting a bit *like* a force on the free charges, causing a current



If you have a 5V supply (emf=5V) connected across a single reistor, the full 5V appears across the resistor (0V on one side, 5V on the other).



But if you have a 5V supply (emf=5V) connected across 2 series resistors of suitable values, you could get the potential on one side of a resisitor 4V, and the potential on the other side 5V. So the potential difference across the resistor is 1V. (The potential difference across the other resistor would be 4V, they add up to 5V.)

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Q3. Understanding potential difference is essential for anyone working with electricity. E.g. (using a voltmeter) you can check safety and find faults.



For an electrician/engineer, understanding voltage is a bit like a doctor understanding blood!



Try the video.

Answer 2

I don't think you totally understood the chapter on potential difference (not meaning to rude because it took me ages to).

Potential difference is often referred to as voltage because the SI unit of pd is volt.

Also, voltage is not exactly the difference in the change of force of a resistor. Pd is the difference of electrical potential between two points. Pd between two points can be defined as the amount of work done to move a unit positive charge from one point to another. (like charges repel so work has to be done to bring two like charges together).

Pd = work done / amount of charge moved

Also, potential difference can't be supplied, it can be applied to make a current move across a resistor. If there is no potential difference there wouldn't be any current moving across a resistor.

I would suggest you to talk to your teacher about this matter as electricity is a really big topic and I can't explain you the full answer to your question right here (it would be too long). You can also try to refer to your textbook.

Answer 3

"voltage" is just a general term for electric potential. Potential can only be described relative to some reference point {typically Earth or ground, or perhaps the negative terminal of a battery or power supply.}



In modern, practical, everyday usage the terms:



"voltage across [a resistor]"

"voltage between [points A and B]"

"potential difference"



are all commonly used, especially by engineers, to describe the same thing.



If I say "the potential difference between the ends of this resistor is 1 volt" I could well be saying:



"The potential at end A is 5V with respect to some zero reference point and the potential at end B is 4V with respect to the same zero reference point."



But it could just as easily be 1000V at A and 999V at B. Who knows? But if we know the value of the resistor and we know the p.d. across it, we can calculate the current flowing through it and the power dissipated in it {as heat} as a result of that current.



Physics purists have historically tended to use "potential difference" to describe that part of a circuit where electrical energy is converted into some other form (heat in resistors and so on)



The "voltage" where some other form of energy is converted into electrical form is usually described as "electromotive force (emf) {from batteries, generators and so on}.



In everyday usage, "A 9V battery" or "A 12V light bulb" would be clearly understood.

Answer 4

@Sea

My understanding, you are trying to be sarcastic about my questions. If you can't help someone, leave it to the others are willing to assist instead of being nasty!

Answer 5

bfd