Why are conductors not used to store electricity?

In summary, capacitors store electrical energy by allowing electrons to flow through them, but a conductor cannot be charged by conduction. A conductor is only charged by induction or friction.
  • #1
NowsTheTime
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I read somewhere that conductors don't really store charge? How can this be correct?

When a conductor is charged by conduction, the electrons spread throughout the surface of the conductor. Doesn't this mean that the capacitor is storing this electricity? What prevents conductors from being used to store electrical energy?
 
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  • #2
Yes, a piece of metal acts like a capacitor and can store some energy.
However the capacitances are too small for practical purposes. Unless the conductors are made really really big in size (see capacitance of the Earth to get some idea)
To increase the capacitance without increasing the size to unpractical values systems of several conductors are used, as in capacitors. Capacitors can store significant amounts of energy.
With the development of super-capacitors, this modality of energy storage has already entered the practical, commercial domain.
 
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  • #3
nasu said:
Yes, a piece of metal acts like a capacitor and can store some energy.
However the capacitances are too small for practical purposes. Unless the conductors are made really really big in size (see capacitance of the Earth to get some idea)
To increase the capacitance without increasing the size to unpractical values systems of several conductors are used, as in capacitors. Capacitors can store significant amounts of energy.
With the development of super-capacitors, this modality of energy storage has already entered the practical, commercial domain.
I see. What factors determine the capacitance of a single conductor?
 
  • #5
NowsTheTime said:
When a conductor is charged by conduction...
A conductor is not charged by conduction. It does not build up more charge when a current is passing through it than when there is no current.
 
  • #6
jbriggs444 said:
A conductor is not charged by conduction. It does not build up more charge when a current is passing through it than when there is no current.
In other words, the electrons are already there, they just start moving when electricity flows. Like a pipe already full of water before you open the tap.
 
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  • #7
russ_watters said:
In other words, the electrons are already there, they just start moving when electricity flows. Like a pipe already full of water before you open the tap.
So why is it that a conductor can go from a charge of 0 coulombs to a charge of -4 coulombs? Aren't electrons entering the conductor and being stored?
 
  • #8
NowsTheTime said:
So why is it that a conductor can go from a charge of 0 coulombs to a charge of -4 coulombs? Aren't electrons entering the conductor and being stored?
They are not. If you shove 4 coulombs of electrons in one end, 4 coulombs come out the other.
 
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  • #9
NowsTheTime said:
Aren't electrons entering the conductor and being stored?

They are exiting as fast as they are entering. Like a pipe.
 
  • #10
That's assuming there is somewhere for them to exit to. If the conductor isn't connected to anything then charge can be stored in the small capacitance between it and earth. However the capacitance is too small to make this useful.
 
  • #11
CWatters said:
That's assuming there is somewhere for them to exit to. If the conductor isn't connected to anything then charge can be stored in the small capacitance between it and earth. However the capacitance is too small to make this useful.
Indeed. We're talking about something much less than a picofarad. Storing 4 Coulombs in a picofarad capacitor... That would require billions of volts, the energy equivalent of several tons of TNT and you'd have exceeded the breakdown voltage of the air by a huge factor before even getting close.
 
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  • #12
jbriggs444 said:
A conductor is not charged by conduction. It does not build up more charge when a current is passing through it than when there is no current.
I think he means "conduction" as used in some introductory text about electrostatics. Is used as one of the modes to charge a neutral body: by touching it with another, charged body. The other modes may be by induction and by friction.
It is not about electrical conduction with the same exact meaning used in the topics about electric current.
A body can be charged by this "conduction".

http://www.physicsclassroom.com/class/estatics/Lesson-2/Charging-by-Conduction
 
  • #13
Vanadium 50 said:
They are exiting as fast as they are entering. Like a pipe.
If electrons exit the conductor as other electrons enter, then why is it that a conductor can have a charge of "n" coulombs?
 
  • #14
nasu said:
I think he means "conduction" as used in some introductory text about electrostatics. Is used as one of the modes to charge a neutral body: by touching it with another, charged body. The other modes may be by induction and by friction.
It is not about electrical conduction with the same exact meaning used in the topics about electric current.
A body can be charged by this "conduction".

http://www.physicsclassroom.com/class/estatics/Lesson-2/Charging-by-Conduction
Yes. That is the definition of conduction that I was referring to.
 
  • #15
NowsTheTime said:
If electrons exit the conductor as other electrons enter, then why is it that a conductor can have a charge of "n" coulombs?

The flow in and out is only equal once the capacitance of the wire is charged. However that happens very quickly because the capacitance is very small.

You cannot put "n coulombs" of charge into the capacitance of a wire. You can put "n coulombs" through a wire. There is a difference.

A small water pipe cannot store a billion cubic feet of water but a billion cubic feet might pass through it.
 
  • #16
There is at least one context where the capacitance to ground is not small: Long-distance high-voltage AC power transmission lines. For example, a 750 kV, 1000 kilometer line. Underground or underwater power cables are even worse.

If you energize one end of such a line, and leave the far end open circuited, then the voltage rises km by km all along the length of the line because of that capacitance. That configuration must be prevented to protect components from overvoltage damage.
 
  • #17
CWatters said:
The flow in and out is only equal once the capacitance of the wire is charged. However that happens very quickly because the capacitance is very small.

jbriggs444 said:
Indeed. We're talking about something much less than a picofarad.

The OP did not specify the size of the conductors, how close they were to the ground or to each other.
 
  • #18
NowsTheTime said:
Yes. That is the definition of conduction that I was referring to.

Then you've been using the wrong name! "Conduction" means the FLOW of charges. You are talking about static electricity, which, by definition, isn't a flow charges. This is why your question created such a confusion.

A conductor cannot store energy efficiently because it has mobile charges, which means that it can easily lose or gain charges simply via contact, even with air! And contrary to our ability to cause static charges in conductors, it really is difficult to get it to store a lot of charges. Think of all the effort one needs to put in in a Van de Graaf generator. And then what happens when you turn it off? How quickly are those charges from the metallic dome dissipated?

Zz.
 
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  • #19
Thank you. You're bringing up some good points. Would it be correct under the broad definition of conduction to call the plates of a capacitor conductors?
 
  • #20
David Lewis said:
Thank you. You're bringing up some good points. Would it be correct under the broad definition of conduction to call the plates of a capacitor conductors?

Conductors are the material. "Conduction" is a process. It is OK to say that the plate of a capacitor is a conductor, because that is the material being used. But under static condition, there is no "conduction".

Zz.
 
  • #21
The term used in school texts is "charging by conduction". So it is a process. There is electron flow from on conductor to another during the charging process so it is not technically wrong. It may be just confusing or not very common.
I think "charging by contact" (used in other sources) is a less confusing one.
 
  • #22
Very good answer. If my understanding (and terminology) are correct, when you first connect a battery to a capacitor, some current does flow, although it might be for a short amount of time.
 
  • #23
David Lewis said:
Very good answer. If my understanding (and terminology) are correct, when you first connect a battery to a capacitor, some current does flow, although it might be for a short amount of time.

That is a transient effect. In fact, this transient current is often used in undergraduate experiments on RC circuits to determine the time constant of that circuit.

But under static condition, which I stated earlier, there is no current flow in the circuit.

Zz.
 
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  • #24
Who said that there is a current under static condition?
 
  • #25
ZapperZ said:
Then you've been using the wrong name! "Conduction" means the FLOW of charges. You are talking about static electricity, which, by definition, isn't a flow charges. This is why your question created such a confusion.

A conductor cannot store energy efficiently because it has mobile charges, which means that it can easily lose or gain charges simply via contact, even with air! And contrary to our ability to cause static charges in conductors, it really is difficult to get it to store a lot of charges. Think of all the effort one needs to put in in a Van de Graaf generator. And then what happens when you turn it off? How quickly are those charges from the metallic dome dissipated?

Zz.
That's very interesting. So how should the question have been wording so as to minimize confusion?
 
  • #26
nasu said:
The term used in school texts is "charging by conduction". So it is a process. There is electron flow from on conductor to another during the charging process so it is not technically wrong. It may be just confusing or not very common.
I think "charging by contact" (used in other sources) is a less confusing one.
Yes, that is exactly what I was referring to: "charging via conduction". This is the term that I was taught to use when referring to the transfer of electrons to the less negative conductor when two conductors of different charges are brought into physical contact with each other. Is there a different term used to describe this same process?
 
  • #27
ZapperZ said:
And contrary to our ability to cause static charges in conductors, it really is difficult to get it to store a lot of charges. Think of all the effort one needs to put in in a Van de Graaf generator.

Maybe the problem is more storing charge at high voltage than storing a lot of charge per se.
 

Related to Why are conductors not used to store electricity?

1. Why can't conductors be used to store electricity?

Conductors, such as copper wires, are materials that allow electricity to flow through them easily. However, they do not have the ability to store or hold onto electricity. This is because their atomic structure allows electrons to move freely, making it difficult to keep them in one place.

2. Can't we just use larger conductors to store more electricity?

Using larger conductors does not increase their ability to store electricity. In fact, it can actually decrease their efficiency as more energy is lost through resistance in the wire. Additionally, larger conductors also require more material and can be costly to produce.

3. Why are conductors not used in batteries to store electricity?

Batteries are a type of energy storage device that use chemical reactions to store and release electricity. Conductors, being purely physical materials, do not have the chemical properties necessary to store electricity in this manner. Therefore, they cannot be used in batteries.

4. What materials are used to store electricity instead of conductors?

There are various materials used for storing electricity, depending on the type of energy storage device. For example, batteries use chemicals, capacitors use insulators and semiconductors, and flywheels use mechanical energy. Each of these materials have unique properties that allow them to store electricity in different ways.

5. Can conductors be used to store electricity at all?

Technically, conductors can store a small amount of electricity due to their capacitance, which is the ability to store an electric charge. However, this capacitance is very low compared to materials specifically designed for energy storage, making conductors impractical for this purpose.

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