Is it Weird?

Is it weird that even after completing IGCSE course, I still don't understand clearly what a volt or emf is. 1V = 1J/C. I have a voltage of 5V and 100V. Does this mean that 1 coulomb of electrons in 5V have energy of 5J and 100V have energy 100J. What does it mean to have higher energy? Also, what makes something to be at a higher potential than other?

Or why is high voltage used in transmission (I have read bad explanations from teachers like heat lost = power = IR^2 etc. Just doesn't make sense. Power can also be written as V^2/R. Now what huh?). I don't understand how number of turns in a transformer affects the voltage either or what is meant by having stability in the nucleus of an atom.

None of this is in the syllabus or at least isn't clearly explained and whenever I try to understand the concepts, I get even more confused. I get it that Physics is a completely experimental field and stuff can't be rigorously proven using a set of axioms like mathematics but I don't even have the slightest intuition.

Am I the only one? Physics exam is in 3 days. I don't even expect any good questions to pop up.

(edited 6 years ago)

Reply 1

Kiritsugu

18

Original post by esrever

Is it weird that even after completing IGCSE course, I still don't understand clearly what a volt or emf is. 1V = 1J/C. I have a voltage of 5V and 100V. Does this mean that 1 coulomb of electrons in 5V have energy of 5J and 100V have energy 100J. What does it mean to have higher energy? Also, what makes something to be at a higher potential than other?

Or why is high voltage used in transmission (I have read bad explanations from teachers like heat lost = power = IR^2 etc. Just doesn't make sense. Power can also be written as V^2/R. Now what huh?). I don't understand how number of turns in a transformer affects the voltage either or what is meant by having stability in the nucleus of an atom.

None of this is in the syllabus or at least isn't clearly explained and whenever I try to understand the concepts, I get even more confused. I get it that Physics is a completely experimental field and stuff can't be rigorously proven using a set of axioms like mathematics but I don't even have the slightest intuition.

Am I the only one? Physics exam is in 3 days. I don't even expect any good questions to pop up.

If you've just learned information for the exam, then you'll never remember it. Learning is a continuous process - you learn properly in the first place; that sets you up to be able to revise effectively - and if you don't review/revise, you'll forget it naturally like all people.

What do you mean you don't expect any "good" questions to pop up? Do you mean good as in you can easily answer them, or good as in interesting...?

It helped me to understand physics when I had a personal tutor. Maybe you should consider getting one, though, your exam is in 3 days so past papers would probably be your best bet - nevertheless it wouldn't hurt. Look at the syllabus and specimen papers to see exactly the kind of questions you'll be getting. If it's understanding, well ask a professional such as a teacher, to help you with that. Is it that you don't remember concepts or is it that you're seeking answers that are out of the scope of the syllabus or maybe it's just not thoroughly learning about it?

If it's learning, increase your study skills. Watch some of the stuff on this first YouTube page - you might realise you're not actually learning in the most efficient way: https://www.youtube.com/results?search_query=How+to+study+better

(edited 6 years ago)

Reply 2

esrever

OP

20

Thanks a lot for the reply. I am not having any difficulty learning the syllabus. By 'not good questions' I meant boring questions. Almost all past papers have same fruitless problems. The things that I talked about aren't required to complete the syllabus so they are sort of 'out of the scope', despite of being essential for understanding. However due to being out of scope, my textbook and teacher have completely ignored them. I was just curious if this is the same with others...

Reply 3

Kiritsugu

18

Original post by esrever

Thanks a lot for the reply. I am not having any difficulty learning the syllabus. By 'not good questions' I meant boring questions. Almost all past papers have same fruitless problems. The things that I talked about aren't required to complete the syllabus so they are sort of 'out of the scope', despite of being essential for understanding. However due to being out of scope, my textbook and teacher have completely ignored them. I was just curious if this is the same with others...

No I've had a similar experience - it's just difficult to explain those things sometimes in a way that we'll understand - they told me I just have to accept that it's the "convention" that's used. By the way, what is a "fruitless problem" for you? Do you mean something that has no real-life application and is just a bunch of theory questions? I'm sure they're trying to make the exams more applicable to real life though, alas, they're merely trying.

Perhaps push your teachers more to squeeze the answers out of them and then do some more research, unless that's what you already do.

Reply 4

esrever

OP

20

But fruitless, I mean problems are really straightforward and not at all rewarding for anyone who has actually put in efforts.

I guess I'll try to talk to my teachers. I did research before but it didn't really help. I get the same conventional responses. IGCSEs are almost done for now. For A levels, I'll not study the school book and find a more in-depth book instead I guess.

Reply 5

RogerOxon

21

Original post by esrever

Is it weird that even after completing IGCSE course, I still don't understand clearly what a volt or emf is. 1V = 1J/C. I have a voltage of 5V and 100V. Does this mean that 1 coulomb of electrons in 5V have energy of 5J and 100V have energy 100J. What does it mean to have higher energy? Also, what makes something to be at a higher potential than other?
No - all too common.

Think of it like the water system in your house. The voltage difference is effectively the pressure difference (actually force, but you get the point). It pushes the current (water flow) - Electromotive Force (EMF) is the best way of thinking about it IMO. A higher pressure (actually force, EMF) difference will drive the water more quickly, so it will have more energy per unit volume (charge).

Or why is high voltage used in transmission (I have read bad explanations from teachers like heat lost = power = IR^2 etc. Just doesn't make sense. Power can also be written as V^2/R. Now what huh?). I don't understand how number of turns in a transformer affects the voltage either or what is meant by having stability in the nucleus of an atom.

P=I^2R=\frac{V^2}{R}

You want to minimise the loss. R is fixed by the cables that you have. The voltage drop across the cables is fixed by R and I, but is NOT the voltage of the power supply - it's just

IR

. The current is therefore the direct way to calculate the power lost - you want to minimise it, so you maximise the SUPPLY voltage to get the same power transferred whilst minimising the power lost in the cables.

(edited 6 years ago)

Reply 6

Thachi3

12

Original post by esrever

Is it weird that even after completing IGCSE course, I still don't understand clearly what a volt or emf is. 1V = 1J/C. I have a voltage of 5V and 100V. Does this mean that 1 coulomb of electrons in 5V have energy of 5J and 100V have energy 100J. What does it mean to have higher energy? Also, what makes something to be at a higher potential than other?

Or why is high voltage used in transmission (I have read bad explanations from teachers like heat lost = power = IR^2 etc. Just doesn't make sense. Power can also be written as V^2/R. Now what huh?). I don't understand how number of turns in a transformer affects the voltage either or what is meant by having stability in the nucleus of an atom.

None of this is in the syllabus or at least isn't clearly explained and whenever I try to understand the concepts, I get even more confused. I get it that Physics is a completely experimental field and stuff can't be rigorously proven using a set of axioms like mathematics but I don't even have the slightest intuition.

Am I the only one? Physics exam is in 3 days. I don't even expect any good questions to pop up.

Hey, i'll be doing the same paper so kind of familiar with the problems.

5V refers to 5J/C. That means that 5J of electrical energy will be changed to other forms of energy each time 1C passes through the component.
Voltage determines the potential of the component. Higher energy means more joules, so more current is passed.

If you are able to understand fractions, you can understand transformers.
Power is equals to current* voltage. Rearranging gives current equals to power/voltage. Therefore, if voltage is high then current is less. This is the main theory that transformers work under.
When current is high, the cable used to send the current must be wide and expensive and also large amounts of heat is lost, reducing the final capacity of energy.
Step up transformer is used to increase voltage on the receiving end, and thereby decreases current, this is used for transmission of energy across the National Grid, right after the generation of electricity.
Step down transformers is used to decrease voltage, increase the current and is used while current reaches homes.

Stability in the nucleus refers to the balance of the nuclear force and electric force. An increase or reduction in neutrons will affect the stability.

Hope it helps

Reply 7

esrever

OP

20

Original post by RogerOxon

No - all too common.

Think of it like the water system in your house. The voltage difference is effectively the pressure difference (actually force, but you get the point). It pushes the current (water flow) - Electromotive Force (EMF) is the best way of thinking about it IMO. A higher pressure (actually force, EMF) difference will drive the water more quickly, so it will have more energy per unit volume (charge).

P=I^2R=\frac{V^2}{R}

You want to minimise the loss. R is fixed by the cables that you have. The voltage drop across the cables is fixed by R and I, but is NOT the voltage of the power supply - it's just

IR

. The current is therefore the direct way to calculate the power lost - you want to minimise it, so you maximise the SUPPLY voltage to get the same power transferred whilst minimising the power lost in the cables.

Thanks a lot for the reply! But I have a few questions. I can't really comprehend how 1 packet of coulomb would have more energy than another. So does this mean that electrons possess a greater internal energy? Or they move faster and have more kinetic energy?
Also, how does having more internal/kinetic energy cause the electrons to move to a region of lower internal/kinetic energy?

Reply 8

Manuster

12

Original post by Kiritsugu

No I've had a similar experience - it's just difficult to explain those things sometimes in a way that we'll understand - they told me I just have to accept that it's the "convention" that's used. By the way, what is a "fruitless problem" for you? Do you mean something that has no real-life application and is just a bunch of theory questions? I'm sure they're trying to make the exams more applicable to real life though, alas, they're merely trying.

Perhaps push your teachers more to squeeze the answers out of them and then do some more research, unless that's what you already do.

It's true, Physics teachers often struggle to help their students understand things. I'm not sure if this is a failure in approach or a complication of the subject. I feel as though they teach it like Maths, which is essentially a long list of rules and equations that must be practiced until memorised. 1 + 1 = 2. It just is...

In Physics however, 1 Ohm + 1 Ohm = 2 Ohms ONLY when the resistors are in series. Whereas 1 Ohm + 1 Ohm = 1/2 Ohms ONLY when the resistors are in parallel.

Why?

Do you know?

I don't....

It just is....

Reply 9

RogerOxon

21

Original post by esrever

I can't really comprehend how 1 packet of coulomb would have more energy than another.

Now you're testing my understanding :smile:

The electrons don't have more energy to begin with - remember voltage (EMF) is a difference, not an absolute. The (force) field does work on the electrons as they pass through it, which can give them more kinetic energy, or overcome drag (resistance on them).

You could think of it like gravity - a 1Kg mass has gravitational potential energy (as an electron has electric potential energy), because it's in a force field. The origins of the force field are different (gravitational or electrical), but the concept is the same. The force does work on particles moving through it.

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