Simple conceptual question about Ohm's law

[engineeringstudnt]

Homework Statement

.

Relevant Equations

V=IR I=Q/t

Hİ :) as you know potential difference in point A to B is equal to the battery's voltage and point A's current is equal to point B's current.So current is I=Q/t , there should be equal charge passing through at same time so how could there be potential difference when there is equal amount of electron on each side ?

 

[PeroK]

Homework Statement:: .
Relevant Equations:: V=IR I=Q/t

View attachment 293404
Hİ :) as you know potential difference in point A to B is equal to the battery's voltage and point A's current is equal to point B's current.So current is I=Q/t , there should be equal charge passing through at same time so how could there be potential difference when there is equal amount of electron on each side ?

Are you asking how a battery works?

 

[engineeringstudnt]

Are you asking how a battery works?

no i know how battery's works :) . Terminals create potential difference so that charge flows on wire. my question is: point A and point B has same amount of electrons in time=t let's say(because the current is same).But why there is a potential difference in theese points :)

 

[PeroK]

But why there is a potential difference in theese points :)

I thought that was because of the battery! Take the battery away and you have a neutral wire.

 

[engineeringstudnt]

I thought that was because of the battery! Take the battery away and you have a neutral wire.

lets say we stopped to time for a while. in point A we should saw x electrons and point B we again saw x electrons(because the current are same I=Q/T) . x-x=0 but there should be a potentail difference right ? that is point what i don't understand

 

[PeroK]

lets say we stopped to time for a while. in point A we should saw x electrons and point B we again saw x electrons(because the current are same I=Q/T) . x-x=0 but there should be a potentail difference right ? that is point what i don't understand

The battery creates an electric field, which produces the current.

 

[ergospherical]

lets say we stopped to time for a while. in point A we should saw x electrons and point B we again saw x electrons(because the current are same I=Q/T) . x-x=0 but there should be a potentail difference right ? that is point what i don't understand

The voltage across the resistor isn't related to the relative amounts of charge passing through either terminal of the resistor (which, as you note, are the same), but rather the relative potential energies (per unit charge) of the charges at either terminal of the resistor.

 

[engineeringstudnt]

The voltage across the resistor isn't related to the relative amounts of charge passing through either terminal of the resistor (which, as you note, are the same), but rather the relative potential energies (per unit charge) of the charges at either terminal of the resistor.

thanks for you answer but honestly i still didnt quite get it i guess i should read more :)

 

[PeroK]

thanks for you answer but honestly i still didnt quite get it i guess i should read more :)

Did you know that Werner Heisenberg nearly failed his PhD examination because he didn't know how a battery works?

I suspect that this, therefore, is probably not true:

no i know how battery's works :) .

 

[ergospherical]

thanks for you answer but honestly i still didnt quite get it i guess i should read more :)

In an Ohmic material of length $d$ and resistance $R$, there is an electric field given by $E = IR/d$ (this comes from a more fundamental relationship $j = \sigma E$). As the charges flow through the resistor, the electric field does an amount $Ed = IR$ of work on them. Equivalently, it can be said that the electric potential energy (per unit charge) of the charges decreases by $IR$. This energy is ultimately transferred to the ions in the metal, becoming heat.

 

[phyzguy]

Hİ :) as you know potential difference in point A to B is equal to the battery's voltage and point A's current is equal to point B's current.So current is I=Q/t , there should be equal charge passing through at same time so how could there be potential difference when there is equal amount of electron on each side ?

Think of a river flowing downhill. Look at a higher point and at a lower point on the river. There is the same amount of water flowing at both points, but the water has a higher potential energy at the higher point than at the lower point. The amount of water flowing is analogous to the current, and the height of the water is analogous to the voltage.

 

[engineeringstudnt]

Think of a river flowing downhill. Look at a higher point and at a lower point on the river. There is the same amount of water flowing at both points, but the water has a higher potential energy at the higher point than at the lower point. The amount of water flowing is analogous to the current, and the height of the water is analogous to the voltage.

thanks for the analogy that's actually really helped.but one question if electrons loses of some of their energy when they passed the resistance don't they lose their speed too ? so if its the case current shouldn't be same at the point A and B but they are :d.?

 

[ergospherical]

thanks for the analogy that's actually really helped.but one question if electrons loses of some of their energy when they passed the resistance don't they lose their speed too ? so if its the case current shouldn't be same at the point A and B but they are :d.?

They lose potential energy when the electric field does work on them, but it's assumed that their drift velocity (and therefore also their averaged kinetic energy) is constant. You can imagine that the "excess" kinetic energy gained due to work done by the electric field is immediately transferred away to the ions in the material.

 

[engineeringstudnt]

They lose potential energy when the electric field does work on them, but it's assumed that their drift velocity (and therefore also their averaged kinetic energy) is constant. You can imagine that the "excess" kinetic energy gained due to work done by the electric field is immediately transferred away to the ions in the material.

i really appreciate that thank you very much i get it now :)

 

[berkeman]

Homework Statement:: .
Relevant Equations:: V=IR I=Q/t

So current is I=Q/t

So just to follow up to clear up your notation going forward...

The current is the amount of charge flowing through a cross-section of the wire divided by the time it took for it to flow through that surface. In delta notation is would be I = ΔQ/Δt. In differential notation (like from differential Calculus) and using LaTeX (see the LaTeX Guide at the bottom of the Edit window):
$$ I(t) = \frac{dQ(t)}{dt}$$

 

[phinds]

i really appreciate that thank you very much i get it now :)

Just to be sure, if you are not solid on what "drift velocity" is you should look it up.