Two questions, voltage & AC transmission (1 Viewer)

[killua_3]

i never really understood the concept of voltage so i thought i should ask now before its too late. my teacher always said its a potential difference, but other times she say that it is the push behind the current. so im a bit confused, what the hell is voltage...

also, when power is being transferred from generating station to homes, it uses AC (right?), which means that the current suppose to alternate. ive been given to understand that in a simple circuit, the current alternates between the two terminals, positive and negative, at 50 times per second (in Aus). so how does it alternate in a transmission line? don't tell me that it alternates between the powerstation and the destination... -_-

thanks guys.

 

[k02033]

your teacher is wrong. voltage is not potenial difference. voltage or electric potenial is a measurment of the electric field over a certain region of space. It gives you an idea as to how the electric field will behave over a certain path. (we usually say voltage between 2 points, those two points are the start and end of the path )

now the term "potenial difference" appearing in electromagnetism is the EXACT same thing that you meet in space, so newton's stuff and the energy theorm. the familar one, U(x)=-GmM/x is the gravitation potenial, and using U(xf)-U(xi) we can measure the change in energy of a system consisting of 2 objects experiencing the gravitational force. in electromagnetism its no different, the system is usually charge particle and an electric field, and the electrical potenial difference measures the changes in that system's energy due to the force that the E field imposes on the charge particle. so potenial diff is total differnt to voltage

 

[k02033]

this is voltage

in the case of uniform E field over span over distance of d, and path of integral is parrallel to E field and both points in the same direction then voltage for this set up is





note voltage is sign sensitive depending on how the path is orientated to E field, HSC water it down and they give you the magnitude of voltage of constant E field of this particular set up in the formula sheet.

 

[k02033]

the above set up corresponds to stoping voltage in the photoelectric effect,
and the potenial difference that the voltage generates is given by



where is the electrical potenial difference

note q is sign sensitive, ie if we place an electron into E field, we have to put q=-1.6*10^-19

 

[killua_3]

ok, i think i get it. but to be precise, what is the difference between potential difference and electrical potential difference. because at the beginning, u said that voltage is not a potential difference, but an electrical potential difference.

 

[k02033]

voltage is not potenial difference. voltage or electric potenial

voltage has another name "electrical potenial" and voltage is not the same as electrical potenial difference, physics has misleading terms sometimes.

 

[k02033]

u said that voltage is not a potential difference, but an electrical potential difference.

i dont think i said that... if somehow i have can you quote it?

 

[k02033]

electrical potenial difference and potenial difference are really the same term, i say electrical potenial difference to point out the fact that a potenial difference has occurred as a result of an electromagnetic phenomena

 

[killua_3]

your teacher is wrong. voltage is not potenial difference. voltage or electric potenial is a measurment of the electric field over a certain region of space.

that's when you told me voltage is not potential difference...

so voltage is electrical potential difference, and the pressure or push behind the electrons?

 

[k02033]

that's when you told me voltage is not potential difference...

so voltage is electrical potential difference, and the pressure or push behind the electrons?

i have never said voltage is electrical potential difference, you are not reading my post carefully enough/

 

[helper]

that's when you told me voltage is not potential difference...

so voltage is electrical potential difference, and the pressure or push behind the electrons?

No it isn't the push as in a force or pressure.

 

[killua_3]

i have never said voltage is electrical potential difference, you are not reading my post carefully enough/

sorry k02033, i'm just really confused with physics at the moment. i think it would be best if i come back to this again with a fresher mind. thanks for your help.

 

[k02033]

ok i just read my explanation on voltage again, and it sucks, (its a kind of hard to explain and teach on forums)
if no one else comes up with better one soon, i will try to explain again