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# So I am starting As physics and I slept through GCSE watch

1. I don't mean that I didn't work hard in GCSE, well I kind of didn't but that's not the point...I just came to realize that I didn't really think as deeply or question what I learnt in GCSE physics as much as I should've done. So for example, can some please explain as truthfully as possible what electricity is ( it's current but then what is current, current is flow electron and electron is actually made up of charge which is coulombs??) right now for me these are just words and at GCSE I would've just gone with it cause I did last minute revision and I gave myself no time to process the depth of it but I feel as though I am lacking the basic concept and understanding now.
If you were to explain to a total newb how would you describe what charge/ coulomb is and also with detail?

This next question might be stupid af...but what's the difference between flow of electrons and free electrons? Free electrons in metal, when metal is heated, diffuse out and collide with other atom...this is correct right? So doesn't this mean that there is a flow/movement of electrons which is the same as current???

One last question, I know that the potential difference of a cell is basically how much energy each electron delivers, so in a series circuit the p.d. is shared. This would mean that if there were two component with the same resistance, then it would mean same current and therefore amount of electrons are passing the component per second, but because there is two component the p.d. is shared, so if total p.d. was 4V, it would be 2 V for each component. How and why, how did they come to this rule? I am thinking that if it passes through the first component then why doesn't that component just use 4 V, after all isn't it how much energy the cell delivers so why is it not able to deliver the same amount for both component? Voltage pushes electrons around in a circuit so why wouldn't the first component get the full energy from the electron cause nothing else has came between it ?

I am very confused and I am pretty sure I have my rules of circuit and electricity pretty messed up. Please help me...I honestly tried to go over the GCSE physics book again and this why on the second time, I realized that I actually don't understand most parts of what they are saying and the reason behind the rules...or even the true meaning of some of these words.

Thanks!!!

Electrons are little things with mass and charge. When they move around you have a current, because current is moving charge. We could express charge in terms of the charge of an electron, then express current in terms of how many electrons pass through an area every second.

But since the electrons charge is so small, we'd end up saying things like "this balloon had a charge of thirteen trillion billion electrons", or "this kettle is rated to ten trillion trillion billion electrons per second".

So we use coulombs, which is the charge of a very large number of electrons, and amperes, which is the current due to a coulomb passing through some area per second. It's just easier in the world of humans to use these units.

Does everything make sense so far?
By the way you're not alone. This is a notoriously misunderstood topic, so please say if it still doesn't make sense.
3. I chose AS physics after not knowing it very well in school, I just crawled my way through it with guesswork and dropped it for A2. Don't know if that's an option for you though.
4. Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse.

I think the key is understanding what's got to be conserved , the circuit rules we have work because of conservation - especially conservation of charge and conservation of energy. If your AS teacher isn't spelling out what's being conserved in each area of study it's probably worth asking them to tell you.

e,g, in your series resistances the current through the +ve terminal of the battery has got to be the same as the current going into the first resistor.

the current coming out of the first resistor has got to be equal to the current going into the first resistor

the current going into the second resistor has got to be equal to the current coming out of the first resistor

and so on all the way back to the battery -ve terminal

it all happens instantly (or at least the speed of light), the current isn't like a truck full of energy that comes out of the battery and could arbitrarily decide to tip it all off at the first resistor - the energy is being converted (to heat) by getting the current through the resistors, if all the energy goes into heating the first resistor there's no energy left to get the current through the second resistor.

this is because charge is being conserved and isn't being created or destroyed, it can't leak out of the circuit and the current can't go into the first resistor, get tired and decide not to come out again.
5. (Original post by Outofthisworld)

...I am thinking that if it passes through the first component then why doesn't that component just use 4 V, after all isn't it how much energy the cell delivers so why is it not able to deliver the same amount for both component? Voltage pushes electrons around in a circuit so why wouldn't the first component get the full energy from the electron cause nothing else has came between it ?
I think I've come up with a better explanation than before

you seem OK with the DC current being the same at all points on the circuit when the resistors are in series, formally this is called Kirchoffs current law (fwiw it doesn't matter if you've been taught the name or not yet)

Ohms law is the law linking voltage, current and resistance... it doesn't just tell you how much current goes through a resistor at a given voltage, it also tells you how much voltage must be across a resistor if it's got a certain current going through it.

both these laws need to be obeyed at the same time, which is why the voltage is shared across the series resistors.
6. (Original post by JCal)
I chose AS physics after not knowing it very well in school, I just crawled my way through it with guesswork and dropped it for A2. Don't know if that's an option for you though.
No, it isn't XD...what grade did you achieve for As (if you don't mind telling me that is) ?
7. (Original post by Joinedup)
Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse.

I think the key is understanding what's got to be conserved , the circuit rules we have work because of conservation - especially conservation of charge and conservation of energy. If your AS teacher isn't spelling out what's being conserved in each area of study it's probably worth asking them to tell you.

e,g, in your series resistances the current through the +ve terminal of the battery has got to be the same as the current going into the first resistor.

the current coming out of the first resistor has got to be equal to the current going into the first resistor

the current going into the second resistor has got to be equal to the current coming out of the first resistor

and so on all the way back to the battery -ve terminal

it all happens instantly (or at least the speed of light), the current isn't like a truck full of energy that comes out of the battery and could arbitrarily decide to tip it all off at the first resistor - the energy is being converted (to heat) by getting the current through the resistors, if all the energy goes into heating the first resistor there's no energy left to get the current through the second resistor.

this is because charge is being conserved and isn't being created or destroyed, it can't leak out of the circuit and the current can't go into the first resistor, get tired and decide not to come out again.
Thanks, kind of helped me to visualise it a bit more clearly. I knew about the rule of conservation of energy but didn't really know that charge behaved in the same way.
8. (Original post by Joinedup)
I think I've come up with a better explanation than before

you seem OK with the DC current being the same at all points on the circuit when the resistors are in series, formally this is called Kirchoffs current law (fwiw it doesn't matter if you've been taught the name or not yet)

Ohms law is the law linking voltage, current and resistance... it doesn't just tell you how much current goes through a resistor at a given voltage, it also tells you how much voltage must be across a resistor if it's got a certain current going through it.

both these laws need to be obeyed at the same time, which is why the voltage is shared across the series resistors.
Thanks again, and this would mean that if I had the resistance and the current then I would be able to use the formula to work out voltage. Also, now that I think about it, it would make sense that voltage would have to be shared because the resistance differs unless it's the same component and that would mean that not all energy would be transferred/ used by the first component.

I have another question; what actually happens when the current after going through the component flows back out through the cell/battery? does it recharge ?
9. (Original post by mik1a)

Electrons are little things with mass and charge. When they move around you have a current, because current is moving charge. We could express charge in terms of the charge of an electron, then express current in terms of how many electrons pass through an area every second.

But since the electrons charge is so small, we'd end up saying things like "this balloon had a charge of thirteen trillion billion electrons", or "this kettle is rated to ten trillion trillion billion electrons per second".

So we use coulombs, which is the charge of a very large number of electrons, and amperes, which is the current due to a coulomb passing through some area per second. It's just easier in the world of humans to use these units.

Does everything make sense so far?
By the way you're not alone. This is a notoriously misunderstood topic, so please say if it still doesn't make sense.
Thanks, so it just means that these are different ways to express charge found in electron in terms of units to make it more simpler for everyone.
10. (Original post by Outofthisworld)
Thanks, so it just means that these are different ways to express charge found in electron in terms of units to make it more simpler for everyone.
That's right. One coulomb of charge is the same as the charge of 6,000,000,000,000,000,000 electrons. One Ampere of current is one coulomb per second, so one Ampere is 6,000,000,000,000,000,000 electrons passing a point on the circuit every second. It's basically a useful time-saving method, but unfortunately it makes an abstract area of physics even more abstract.
11. (Original post by Joinedup)
I think I've come up with a better explanation than before

you seem OK with the DC current being the same at all points on the circuit when the resistors are in series, formally this is called Kirchoffs current law (fwiw it doesn't matter if you've been taught the name or not yet)

Ohms law is the law linking voltage, current and resistance... it doesn't just tell you how much current goes through a resistor at a given voltage, it also tells you how much voltage must be across a resistor if it's got a certain current going through it.

both these laws need to be obeyed at the same time, which is why the voltage is shared across the series resistors.
I beg to differ that it is a better explanation as compared to your previous explanation. I kinda of like your previous explanation.

I seem to understand why you said "Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse. "

Ohm's law is linking current, potential difference and resistance provided the resistor is ohmic materials.

The resistors in any series circuit need not be ohmic materials.

I believe in any examination boards for physics, they have the definition of resistance for a conductor is the ratio of the potential difference across a conductor to the current in the conductor:

----1

This is NOT Ohm's law.

Equation 1 can be called Ohm's law provided is a constant. Equation 1 can also be used when the resistors in the series circuit are non-ohmic.

Again pardon me if you already know about it. But your explanation tells me otherwise. Maybe it is good to make clear for other students as you said, "Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse." ..

To explain clearly what the OP requests is not really an easy task.
12. (Original post by Eimmanuel)
I beg to differ that it is a better explanation as compared to your previous explanation. I kinda of like your previous explanation.

I seem to understand why you said "Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse. "

Ohm's law is linking current, potential difference and resistance provided the resistor is ohmic materials.

The resistors in any series circuit need not be ohmic materials.

I believe in any examination boards for physics, they have the definition of resistance for a conductor is the ratio of the potential difference across a conductor to the current in the conductor:

----1

This is NOT Ohm's law.

Equation 1 can be called Ohm's law provided is a constant. Equation 1 can also be used when the resistors in the series circuit are non-ohmic.

Again pardon me if you already know about it. But your explanation tells me otherwise. Maybe it is good to make clear for other students as you said, "Well tbh the explanations given for circuits make it seem very confusing and arbitrary at gcse." ..

To explain clearly what the OP requests is not really an easy task.
afaik the guy is starting AS and doesn't feel secure in his knowledge of GCSE material so I was trying to offer up an explanation that I think will be helpful rather than give a surrogate A level lesson (which he doesn't seem to have had yet and for all I know might be perfectly good and non confusing when he does get them)

R=V/I occurs in GCSE and continues to appear in the AQA A2 DFB
http://filestore.aqa.org.uk/subjects...NS-JUN12.PDF#2
so seems appropriate IMO
13. (Original post by mik1a)

Electrons are little things with mass and charge. When they move around you have a current, because current is moving charge. We could express charge in terms of the charge of an electron, then express current in terms of how many electrons pass through an area every second.

But since the electrons charge is so small, we'd end up saying things like "this balloon had a charge of thirteen trillion billion electrons", or "this kettle is rated to ten trillion trillion billion electrons per second".

So we use coulombs, which is the charge of a very large number of electrons, and amperes, which is the current due to a coulomb passing through some area per second. It's just easier in the world of humans to use these units.

Does everything make sense so far?
By the way you're not alone. This is a notoriously misunderstood topic, so please say if it still doesn't make sense.
We never went into depth such as this in GCSE Science. Actually, we barely went over the basic fundamentals of electricity and instead, rather worked on equations, Joules, Costings etc...

I would assume that you have not recently done your GCSE's but have probably already done your A-levels etc..
14. (Original post by Outofthisworld)
No, it isn't XD...what grade did you achieve for As (if you don't mind telling me that is) ?
I don't think telling you would be productive to the thread
15. Hi,

As I mentioned in the previous posting that it is not an easy task to explain all the queries in a clear and simple way. I would give a try and if I did it badly, I am sorry about it.

I would break the explanation down into two parts and would make reference to an online free college physics text.
https://openstax.org/details/college-physics

(Original post by Outofthisworld)
So for example, can some please explain as truthfully as possible what electricity is ( it's current but then what is current, current is flow electron and electron is actually made up of charge which is coulombs??) right now for me these are just words and at GCSE I would've just gone with it cause I did last minute revision and I gave myself no time to process the depth of it but I feel as though I am lacking the basic concept and understanding now.
If you were to explain to a total newb how would you describe what charge/ coulomb is and also with detail?
Frankly speaking, I would avoid using the word electricity wherever I can. The word electricity has several meanings attached to it and it really depends on what context is the word being used. Due to its ambiguities, I would not say what is electricity.

Charge is a property that a particle can have and it is measurable, so it is a physical quantity like mass.

Next is regard to the quantization of charge. In simple analogy, we say there is 1 person or 20 people in a room but we can never say there is 0.5 person or 19.7 people because these numbers (0.5, 19.5) don't make sense in the real world. Human exist as discrete individual and cannot be subdivided (or cut) into smaller individual.

Read under the section Charge Carried by Electrons and Protons
This section also describes charges and the BIG unit coulomb.

OR
Read 17.1 Electric Charge and 17.3 Conservation and Quantization of Charge
I think this is a better version.

A better way of thinking current is the rate of flow of charges instead of just electrons. If you have taken chemistry and have encountered electrolysis, the working principle behind is using electric current to decompose compound into their constituent elements. In electrolysis, it is the flow of ions in the solution that constitutes the current.

(Original post by Outofthisworld)
what's the difference between flow of electrons and free electrons?
I am not sure what are you trying to ask. The rate flow of electrons is current. Free electrons mean that can move "freely".

If you are trying to combine the two (flow of electrons and free electrons) together - the flow of electrons (these electrons are the free electrons).

Next, I would recommend that to read up how physicists model current.
Chapter 20.1 Under the section Drift velocity.

It is good that you take times to read the drift velocity part, so that it may be slightly easy for you follow what I would explain in the second part where I would discuss the electrical circuit put for by you.

(Original post by Outofthisworld)
Free electrons in metal, when metal is heated, diffuse out and collide with other atom...this is correct right?
Yes

(Original post by Outofthisworld)
So doesn't this mean that there is a flow/movement of electrons which is the same as current???
You can say so. The situation here is more complex. If you have learnt thermocouple, what you had described is something that would happen in thermocouple. Since I am not an expert on thermocouple, I would go further.

PS: One thing to remember physicists are always building models to explain how nature works. The model can be a diagram which may simplify the complex process, so please don't think it is 100% correct - there is no such model! The model can be just a visual aid to allow us to have an intuitive way of explaining the basic principles.

Hope this one cent helps.
16. (Original post by redsoules)
We never went into depth such as this in GCSE Science. Actually, we barely went over the basic fundamentals of electricity and instead, rather worked on equations, Joules, Costings etc...
That is unfortunate, and I myself was in exactly the same situation.

Even the smartest kids in a GCSE class are passing exams by rote learning, without any true understanding of what's going on. It's a real shame.

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