Is uniform electric field realistic?

[Axe199]

I was learning about gauss's law and how to use to determine electric field, one of them is an infinite plane of continuous and uniform charge , eventually E= σ/2ε which means the E is not depend on the distance from the plane , does that mean anywhere i place a test charge above this plane it will experience the same force? can this happen in reality? or is it just a mathematical term?

 

[Vanadium 50]

A uniform field for all space and all time is impossible, as it doesn't exist here and now. So it's an approximation. Like frictionless planes, stretchless ropes, massless pulleys, etc. That said, it cvan be a useful approximation.

 

[Axe199]

A uniform field for all space and all time is impossible, as it doesn't exist here and now. So it's an approximation. Like frictionless planes, stretchless ropes, massless pulleys, etc. That said, it cvan be a useful approximation.

what about metal they have a similar expression of the E , is that an approximation too? if yes , can we get the real number mathematically or just experimentally?

 

[Vanadium 50]

I don't understand what you are saying.

 

[rcgldr]

In the case of two oppositely charged plates (capacitor), the field between the two plates sufficiently inside the outer edges of the plates is a close approximation to a field of constant intensity.

 

[Axe199]

I don't understand what you are saying.

i meant if we have a conductor , the field expression is σ/ε is this an approximation too?
if it's an approximation , is there a mathematical way to derive an accurate answer ? or the field is determined accurately at a certain point only by experiment?

 

[Matterwave]

i meant if we have a conductor , the field expression is σ/ε is this an approximation too?
if it's an approximation , is there a mathematical way to derive an accurate answer ? or the field is determined accurately at a certain point only by experiment?

You mean for a finite sized charged plate? The field very near the center of the plate will be approximately the expression given. As you get farther from the plate and or closer to the edges the fields will become very different. The strengths as well as directions will change as well. But it's very hard to mathematically derive the fringe fields from first principles because the geometry is too complicated.

 

[jtbell]

There are numerical methods for calculating the field (at least to some level of approximation) in a non-ideal configuration. If you have a specific configuration in mind, someone here might be able to tell you which is the most appropriate method for that configuration.

 

[ZetaOfThree]

i meant if we have a conductor , the field expression is σ/ε is this an approximation too?
if it's an approximation , is there a mathematical way to derive an accurate answer ? or the field is determined accurately at a certain point only by experiment?

The electric field has magnitude $\frac{\sigma}{\epsilon_0}$ only at the surface of the conductor. It might change as you move away from the surface. This expression comes about from assuming that charge smoothly spreads out across the conductor's surface (and that Gauss's law is valid). Of course, charges come in clumps (electrons, etc.) so it's not smooth. So yes, it is an approximation... but a good one.

 

[Axe199]

There are numerical methods for calculating the field (at least to some level of approximation) in a non-ideal configuration. If you have a specific configuration in mind, someone here might be able to tell you which is the most appropriate method for that configuration.

i have a certain setup in mind, for example , the electric field 1 m above the top of a van de graaff generator

 

[Axe199]

The electric field has magnitude $\frac{\sigma}{\epsilon_0}$ only at the surface of the conductor. It might change as you move away from the surface. This expression comes about from assuming that charge smoothly spreads out across the conductor's surface (and that Gauss's law is valid). Of course, charges come in clumps (electrons, etc.) so it's not smooth. So yes, it is an approximation... but a good one.

electrons comes in clumps even in conductors like metals ?

 

[ZetaOfThree]

electrons comes in clumps even in conductors like metals ?

Yeah. "Clump" is my colloquial term for "particle". Electrons are particles.

 

[Axe199]

Yeah. "Clump" is my colloquial term for "particle". Electrons are particles.

okay then , i thought clumps means something like lumps