# Can you explain electricity to me by using equations?

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#1
So this is what I know:

Current is the flow of electrons,potential difference/voltage is how much energy is given to each component.Resistance is how much current you need to allow electrons to flow through the wire as they are colliding with the atoms of the metal wire.

I would like to kindly request if someone may help me and explain to me what P.d,current and resistance actually is by using equations so I can see the relationship between all of them.

For example resistance =p.d/current so the higher the current the lower the resistance as if we had a p.d of 10 and a current of 5 the resistance would be 2 and if the p.d would be 5 and current would be 10 then the resistance would be 0.5 so the bigger the current the smaller the resistance (that is what I think anyway).

Any help using physics equations to explain electricity further would be much appreciated.
0
3 years ago
#2
(Original post by Anonymous1502)
So this is what I know:

Current is the flow of electrons,potential difference/voltage is how much energy is given to each component.Resistance is how much current you need to allow electrons to flow through the wire as they are colliding with the atoms of the metal wire.

I would like to kindly request if someone may help me and explain to me what P.d,current and resistance actually is by using equations so I can see the relationship between all of them.

For example resistance =p.d/current so the higher the current the lower the resistance as if we had a p.d of 10 and a current of 5 the resistance would be 2 and if the p.d would be 5 and current would be 10 then the resistance would be 0.5 so the bigger the current the smaller the resistance (that is what I think anyway).

Any help using physics equations to explain electricity further would be much appreciated.

The thing you're missing to tie these things together is charge.

Potential Difference is the work done per unit charge.
Current is the rate of change of charge.
Resistance is the ratio of potential difference to current.

This is A2 stuff but its not that complicated. Forget about wires and things and Imagine you have a positive charge of 1 unit sitting in space and a negative charge near by - obviously they attract. There is a potential to do work (work = foce * distance) and the force is proportional to the negative charge, so you can define electric potential (not potential difference) as the potential energy that can be turned into kinetic per unit of negative charge when you let the negative charge go an be attracted to the positive one.

Now pick two points around the positive charge and you can define potential difference as the difference in electric potential between the two points. This is an interesting quantity because if you know the charge of a particle and it moves from a point of a certain potential to another point then the net change in energy of the particle will be the potential difference * the charge. So when you see a cell that has +9V and 0V terminals these are potentials and the potential difference is (9 - 0 = 9V).

A current in a wire is, as you said, the flow of charge - so in the previous example if instead of just sending one particle between the two points, you have a whole bunch then to work out the current you'd do the total charge transferred / the time taken.

Resistance is what you need to get back to a wire lab experiments. So you have a potential difference from a battery or power pack and a supply of particles. The resistance is a property of the wire / component and it basically stops all the charge from flowing at once by constraining the charged particles.
1
#3
(Original post by alfredholmes)
The thing you're missing to tie these things together is charge.

Potential Difference is the work done per unit charge.
Current is the rate of change of charge.
Resistance is the ratio of potential difference to current.

This is A2 stuff but its not that complicated. Forget about wires and things and Imagine you have a positive charge of 1 unit sitting in space and a negative charge near by - obviously they attract. There is a potential to do work (work = foce * distance) and the force is proportional to the negative charge, so you can define electric potential (not potential difference) as the potential energy that can be turned into kinetic per unit of negative charge when you let the negative charge go an be attracted to the positive one.

Now pick two points around the positive charge and you can define potential difference as the difference in electric potential between the two points. This is an interesting quantity because if you know the charge of a particle and it moves from a point of a certain potential to another point then the net change in energy of the particle will be the potential difference * the charge. So when you see a cell that has +9V and 0V terminals these are potentials and the potential difference is (9 - 0 = 9V).

A current in a wire is, as you said, the flow of charge - so in the previous example if instead of just sending one particle between the two points, you have a whole bunch then to work out the current you'd do the total charge transferred / the time taken.

Resistance is what you need to get back to a wire lab experiments. So you have a potential difference from a battery or power pack and a supply of particles. The resistance is a property of the wire / component and it basically stops all the charge from flowing at once by constraining the charged particles.
What exacly is charge and what is the difference between pd and potential energy? All the GCSE electricity equations are:

current=charge/time so current is the amount of charge per time (that is what I understand anyway)

p.d=workdone/charge so the energy transfered per charge which is the amount of current in a certain amount of time (energy transfered per current in a set amount of time)

power=energy/time so energy is the amount of power in a certain amount of time so (power in a certain amount of time per an amount of time)

power=current x p.d (p.d is power/current)

energy=p.d x charge

What I really struggle with is that some many equations can be used to work out charge,p.d,energy etc so what does it all mean what is the relationship between them all.I am struggling what each thing means and what determines it as there are so many equations with the same components I just need to tie it all together somehow.

As well as thank you for all your help it is much appreciated.
0
3 years ago
#4
(Original post by Anonymous1502)
What exacly is charge and what is the difference between pd and potential energy? All the GCSE electricity equations are:

current=charge/time so current is the amount of charge per time (that is what I understand anyway)

p.d=workdone/charge so the energy transfered per charge which is the amount of current in a certain amount of time (energy transfered per current in a set amount of time)

power=energy/time so energy is the amount of power in a certain amount of time so (power in a certain amount of time per an amount of time)

power=current x p.d (p.d is power/current)

energy=p.d x charge

What I really struggle with is that some many equations can be used to work out charge,p.d,energy etc so what does it all mean what is the relationship between them all.I am struggling what each thing means and what determines it as there are so many equations with the same components I just need to tie it all together somehow.

As well as thank you for all your help it is much appreciated.
Yeah, when I was doing GCSE and AS all the electricity stuff did seem as if it had all just been made up and things had been pulled from thin air so I'll try to explain, the problem is I suppose you can use basic maths to work out things about circuits you set up, but to understand where the maths comes from requires a bit more maths knowledge.

Charge is just a physical property of a thing (electron, proton, ion, quark etc). Think of it in the same way as you would mass, its just a property that is there. It can be positive, negative or 0. Like charges repel and opposite charges attract. And the magnitude of the force is proportional to both the charges - similar to the way that the gravitational force is proportional to both masses.

The reason there are so many equations that can be used to work out the same thing is that all the equations are basically talking about the same fundamental things just the equations may be better for different cases. The important things are energy, charge and time. All the others are just useful combinations of those things that can be used to solve problems.

The difference between potential energy and p.d can be seen from the equations. Potential energy is the same as work done (basically) just looking at it from a different perspective - ie I have a bulb running off a battery and it releases a total amount of energy before it runs flat (does a total amount of work) or If I plug in this battery to the bulb it has the potential to do this much work. The potential difference (as V = W/Q) is the energy released (or the potential energy that could be released in the future) when a charged particle of charge Q moves through the potential difference.

Hope that helps
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#5
(Original post by alfredholmes)
Yeah, when I was doing GCSE and AS all the electricity stuff did seem as if it had all just been made up and things had been pulled from thin air so I'll try to explain, the problem is I suppose you can use basic maths to work out things about circuits you set up, but to understand where the maths comes from requires a bit more maths knowledge.

Charge is just a physical property of a thing (electron, proton, ion, quark etc). Think of it in the same way as you would mass, its just a property that is there. It can be positive, negative or 0. Like charges repel and opposite charges attract. And the magnitude of the force is proportional to both the charges - similar to the way that the gravitational force is proportional to both masses.

The reason there are so many equations that can be used to work out the same thing is that all the equations are basically talking about the same fundamental things just the equations may be better for different cases. The important things are energy, charge and time. All the others are just useful combinations of those things that can be used to solve problems.

The difference between potential energy and p.d can be seen from the equations. Potential energy is the same as work done (basically) just looking at it from a different perspective - ie I have a bulb running off a battery and it releases a total amount of energy before it runs flat (does a total amount of work) or If I plug in this battery to the bulb it has the potential to do this much work. The potential difference (as V = W/Q) is the energy released (or the potential energy that could be released in the future) when a charged particle of charge Q moves through the potential difference.

Hope that helps
Thank you for your help, I am still not exactly sure how electricity works as there are so many definitions for many things to do with electricity.I am sorry if i am annoying you perhaps as my brain cannot comprehend electricity.What I think is that:

Current is the flow of electrons which carry charge.P.d is the thing that pushes current through and resistance tries to resist the flow of current as electrons collide with atoms of the metal but the p.d. pushes the forward and p.d. shows the amount of something you need to push current through a wire.

My analogy of electricity compared to a water pipe:
Current is the flow of water and p.d. is the force needed to make the water flow forward.Resistance is the thing that stops the water from flowing in a water pipe. Charge shows how much water there is.Correct me fi what i am thinking is wrong.
0
3 years ago
#6
(Original post by Anonymous1502)
Thank you for your help, I am still not exactly sure how electricity works as there are so many definitions for many things to do with electricity.I am sorry if i am annoying you perhaps as my brain cannot comprehend electricity.What I think is that:

Current is the flow of electrons which carry charge.P.d is the thing that pushes current through and resistance tries to resist the flow of current as electrons collide with atoms of the metal but the p.d. pushes the forward and p.d. shows the amount of something you need to push current through a wire.

My analogy of electricity compared to a water pipe:
Current is the flow of water and p.d. is the force needed to make the water flow forward.Resistance is the thing that stops the water from flowing in a water pipe. Charge shows how much water there is.Correct me fi what i am thinking is wrong.
I'm not sure if anyone really knows how it works, perhaps if you could give an example of a gcse question that you don't really know how to answer then I'd be able to help in a more direct way. The analogy is quite good I think, but sometimes in physics things just aren't intuitive.
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