What is voltage and how to look at it intellectually?

[kartikwat]

What is voltage and how to look at it intellectually?

 

[UltrafastPED]

Voltage is something that is measured between two points; if one is taken as ground (=zero volts), then you can state the voltage at each point wrt ground.

The equipotential surface, or surfaces of equal voltages are a most useful tool; the gradient of the potential function yields the force, and so the equipotential surfaces can be used to define the field lines for the forces.

Thus you can work your way back and forth between the electric field and the potential.

The electric field is derived directly from the forces, and is a vector field. The potentials (voltages) are scalars, and are related to the work required to move a charge from here to there - or from ground to here. The voltages convert to potential energy when multiplied by the amount of charge: Potential Energy = voltage difference x amount of charge.

At what level have you studied electromagnetism? What is your interest?

 

[kartikwat]

I have not studied electromagnetism yet .my interest is know the nature but my reading comprehension is not good

 

[UltrafastPED]

Then I recommend a text like Purcell:
https://www.amazon.com/dp/0070049084/?tag=pfamazon01-20

When taught, it is a full semester course. Of course there are other texts, but this one is well suited to self-study, and is widely available. Requires a working knowledge of calculus.

 

[Drakkith]

What is voltage and how to look at it intellectually?

One way is to break it down into the basics. Voltage is the difference in electric potential between two points.

Electric potential is the amount of electric potential energy a unitary charge would have at a point in space.

Electric potential energy is the amount of potential energy that a charge possesses.

So you need to understand what electric potential energy is and work up from there.

 

[kartikwat]

Voltage

Hey drakkith, it is comprehensive to me till the point that voltage is difference in electric potential between 2 points but when it comes to circuitry part with battery included it is out of my comprehension .how to help it

 

[Drakkith]

Well, what's causing the trouble? Remember that a battery is a voltage source, so unless you are wondering about the specifics of how a battery operates you can simply replace the battery with any other voltage source giving the same voltage and the circuit is identical.

 

[kartikwat]

Voktage

The cicruitry part gives me terror

 

[Drakkith]

Okay. Can you be a bit more specific with where you are having trouble?

 

[atyy]

Voltage is the colloquial term for difference in electric potential between two nearby points, and also called the potential difference.

The electric potential is a number that we can assign to every point in space to characterize exactly an electric field that is not changing in time, or approximately an electric field that is only slowly changing with time. The potential itself does not directly tell us about the electric field, but the difference in potential between two nearby points does tell us directly about the electric field. If the potential at point A is higher than at point B, a small positive test charge placed at point A will accelerate towards point B. The bigger the difference in potential between point A and point B, the larger will be the acceleration of the small positive test charge.

Let's say you have two metal plates separated by air. On plate A you put positive charge, on plate B you put negative charge. The electric potential at plate A will be higher than at plate B, indicating that the positive charge on plate A is attracted to plate B. If the potential difference is not too large, the air between the plates is an insulator and the charge will not move. If we connect the two plates with a wire, the positive charge on plate A will flow through the wire towards plate B and neutralize the charge there. After some time, there will not be any more charge on either plate, and the current will stop flowing.

A battery is like the two plates with positive and negative charge, except that unlike the plate, a chemical reaction keeps on producing positive charge at one terminal, and negative charge at the other terminal, so that the current does not quickly stop.

 

[kartikwat]

See,when battery is connected in circuits,based on my reading battery creates potential difference which start the charge to move. when the charge reaches capacitor in series what happens after that is creating a trouble

 

[Drakkith]

See,when battery is connected in circuits,based on my reading battery creates potential difference which start the charge to move. when the charge reaches capacitor in series what happens after that is creating a trouble

Let's label our 2 capacitors as C1 and C2 and connect plate 1 of C1 to the negative terminal of the battery, and plate 2 of C2 to the positive terminal. When you connect the battery current begins to flow throughout the entire circuit, not just in one spot. (In the example below, I'm using electrons as my charges)

Charges begin to move on and off the plates of the capacitors. Charges move from the negative terminal of the battery and build up on plate 1 of C1, negatively charging it. Charges move off of plate 2 of C1, positively charging it, and move to plate 1 of C2, negatively charging it. Charges move off of plate 2 of C2 to the positive terminal of the battery, positively charging the plate. (All this effectively happens simultaneously)

The end result is that the plates end up charged similarly to the diagram in your attachments in your capacitor thread.

 

[Delta2]

See,when battery is connected in circuits,based on my reading battery creates potential difference which start the charge to move. when the charge reaches capacitor in series what happens after that is creating a trouble

So, you understand what is happening when the battery charges one capacitor, but you have problem understanding the charging of capacitors in series?

 

[kartikwat]

Voltage

Yes you are saying right and what causes potential drop when charge passes through capacitor

 

[Drakkith]

I believe it is the buildup of the electric field in the capacitor. When you first connect the battery the capacitor is uncharged and acts like a short. Therefore it has very little voltage drop across it. As the plates charge the electric field builds up, requiring more work to move each charge and increasing the voltage drop across the capacitor. Someone correct me if I'm wrong.

 

[kartikwat]

Voltage

@drakkith what happens if we introduce mica between the plates of capacitor (1)when the voltage supply remain connected(2)after the supply was disconnected

 

[Drakkith]

What's mica?

 

[Delta2]

I believe it is the buildup of the electric field in the capacitor. When you first connect the battery the capacitor is uncharged and acts like a short. Therefore it has very little voltage drop across it. As the plates charge the electric field builds up, requiring more work to move each charge and increasing the voltage drop across the capacitor. Someone correct me if I'm wrong.

Well that's another theoretical problem, if the potential creates the field or the field creates the potential but i believe in most textbooks about classical electromagnetism, first they define the electric field (as being created by electric charges) and then they define the potential (as the line integral of electric field between a point and the infinite).

However nowdays the scalar and the vector potential of the electromagnetic field are considered to be more fundamental than the field.

 

[kartikwat]

Voltage

Mica is A dielectric

 

[CWatters]

Yes you are saying right and what causes potential drop when charge passes through capacitor

Individual charges do not pass through a capacitor. Charge arrives on one plate and repels like charges from the other plate. You end up with a different charge on each plate. It's this that causes a voltage to appear between the plates.

 

[UltrafastPED]

What's mica?

Mica is a very important mineral; it often appears as shiny specks, but also forms large sheets. In the sheet form it can be split into very fine, very clean layers.

See https://en.wikipedia.org/wiki/Mica

 

[Drakkith]

@drakkith what happens if we introduce mica between the plates of capacitor (1)when the voltage supply remain connected(2)after the supply was disconnected

That's a complicated issue that's probably best left until you know more about electronics.

 

[jtbell]

What is voltage and how to look at it intellectually?

Let's make an analogy, by first talking about gravity instead of electricity.

Suppose we have a 1 kg object resting on the ground. We lift it to a height of h = 2 m and hold it stationary there. We have to do work against the gravitational force: W = Fh = mgh = (1 kg)(9.8 m/s²)(2 m) = 19.6 J. We say the object now has 19.6 J of gravitational potential energy with respect to the ground. (I hope you've already studied potential energy in mechanics so this is just a review for you!)

An object with a mass of 2 kg at that height would have twice as much potential energy, 39.2 J. The potential energy of an object at a given height depends on its mass. However, we can say that any object at a height of 2 m has 19.6 J of potential energy per kg of mass. We can say that a location 2 m above the ground has a gravitational potential (note I didn't say "energy") of 19.6 J/kg. If we wanted to give the unit "J/kg" a name, we might call it a "gravolt." Any object placed at that height has gravitational potential energy equal to its mass times the gravitational potential ("gravoltage") at that location.

Now imagine that instead of a gravitational field, we have an electric field E in the downwards direction with a magnitude of 9.8 N/coulomb; and an object with +1 coulomb of charge. To lift the object to a certain height, we have to do work against the electrical force: W = Fh = qEh. The rest of the discussion is the same as above, except that we rename:

mass --> charge (and kg --> coulomb)
gravitational potential energy --> electric potential energy
gravitational potential --> electric potential
"gravoltage" --> voltage (J/kg --> J/coulomb = volt)

 

[atyy]

Individual charges do not pass through a capacitor. Charge arrives on one plate and repels like charges from the other plate. You end up with a different charge on each plate. It's this that causes a voltage to appear between the plates.

Yes, indeed, that's a very important point.

 

[DiracPool]

Then I recommend a text like Purcell:
https://www.amazon.com/dp/0070049084/?tag=pfamazon01-20

When taught, it is a full semester course. Of course there are other texts, but this one is well suited to self-study, and is widely available. Requires a working knowledge of calculus.

Are you just recommending Volume 2? What about Volume 1? Is this it?

https://www.amazon.com/dp/1107014026/?tag=pfamazon01-20

 

[UltrafastPED]

Are you just recommending Volume 2? What about Volume 1? Is this it?

https://www.amazon.com/dp/1107014026/?tag=pfamazon01-20

Yes, that is an updated version of the Purcell text.

The link I posted was to the Berkeley Physics Course, of which Purcell is the second volume. The complete series is 5 volumes, and they make a great introduction to physics at the undergraduate level.

See https://en.wikipedia.org/wiki/Berkeley_Physics_Course

Note especially the comment about their choice of gaussian units - ughh! That is the one point which I disliked. The edition which you located is in SI.

I am particularly fond of volume IV, Quantum Physics, by Wichmann. It focuses on the experimental basis for quantum physics, presented with historic foot notes, as opposed to the mathematical structure of quantum mechanics. This material is usually taught as a portion of a Modern Physics course today, but I like the fuller treatment. It makes for good reading, and great reference material when trying to understand these difficult issues.

 

[kartikwat]

Let's make an analogy, by first talking about gravity instead of electricity.

Suppose we have a 1 kg object resting on the ground. We lift it to a height of h = 2 m and hold it stationary there. We have to do work against the gravitational force: W = Fh = mgh = (1 kg)(9.8 m/s²)(2 m) = 19.6 J. We say the object now has 19.6 J of gravitational potential energy with respect to the ground. (I hope you've already studied potential energy in mechanics so this is just a review for you!)

An object with a mass of 2 kg at that height would have twice as much potential energy, 39.2 J. The potential energy of an object at a given height depends on its mass. However, we can say that any object at a height of 2 m has 19.6 J of potential energy per kg of mass. We can say that a location 2 m above the ground has a gravitational potential (note I didn't say "energy") of 19.6 J/kg. If we wanted to give the unit "J/kg" a name, we might call it a "gravolt." Any object placed at that height has gravitational potential energy equal to its mass times the gravitational potential ("gravoltage") at that location.

Now imagine that instead of a gravitational field, we have an electric field E in the downwards direction with a magnitude of 9.8 N/coulomb; and an object with +1 coulomb of charge. To lift the object to a certain height, we have to do work against the electrical force: W = Fh = qEh. The rest of the discussion is the same as above, except that we rename:

mass --> charge (and kg --> coulomb)
gravitational potential energy --> electric potential energy
gravitational potential --> electric potential
"gravoltage" --> voltage (J/kg --> J/coulomb = volt)

But in this case where is electrical potential energy 0

 

[kartikwat]

That's a complicated issue that's probably best left until you know more about electronics.

I got what happens when mica is introduced between the plates of capacitor(1)when the voltage source is connected there is no change in voltage.capacitance change by factor ok dielectric constant abd so on(2)when voltage source is disconnected charge remain same andnagain capacitance change by factor of dielectric constant of medium.

 

[jeffery_winkle]

The volt is a unit of electromotive potential, where 1 volt = 1 joule/coulomb

The joule is a unit of energy, where 1 joule = 1 kg m^2/s^2

The coulomb is a unit of electric charge, where the charge of one electron is -1.06 x 10^-19 C

Also

1 amp = 1 coulomb/second

1 watt = 1 joule/second

 

[jtbell]

But in this case where is electrical potential energy 0

At ground level, same as with gravitational potential energy. It takes zero work to raise an object from ground level to ground level, i.e. keep it where it is, for both the gravitational force and the electrical force, in the situations that I described.

Potential energy (of whatever kind: gravitational, electrical, elastic (spring)...) is always with respect to some location at which we define the potential energy to be zero.

However, the choice of location for zero potential energy doesn't matter as far as physical results are concerned, because those always depend on the difference in PE between two locations. So long as we stick with the same definition for "zero potential energy" throughout a given problem, we're OK.

Likewise, in an electrical circuit problem, it doesn't matter which point we choose to have the potential = 0 (the "ground" or "earth"), so long as we stick to that choice throughout the problem.

 

[jim hardy]

What is voltage and how to look at it intellectually?

For me the concept of absolute potential was a breakthrough.
Hyperphysics has concise demonstrations at
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html
and
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.htmlI hope following is the type of answer you sought - i sure didn't intend to "talk down".
I remember struggling with the basic concepts - with all the units named after people rather than mnemonically it's hard to keep them straight.
......................

It may help to make things a little bit visceral.

Take two good refrigerator magnets, one in each hand.
Note their attractive force when opposite poles are brought near one another
and their repulsive force when like poles are brought near

Now - you know very well electric charge acts the same way, likes repel and opposites attract. You've experienced it when removing one styrofoam cup from a stack, or the plastic bag from a wool sweater fresh from the cleaners.

Voltage is a measure of the work done in moving an electric charge over a distance against such a magnetic or electrical force.
But that's a bit foggy-----

You need to grasp the concept of potential.
Then the concept of voltage's other name, potential difference, will come clear.

Absolute Potential is the work expended against that magnetic or electrical force in moving a unit of charge from infinity to wherever it is you are.
It's simply Work = Force X Distance. Probably with an integral sign...
But that's totally impractical - who could go out to infinity to make the measurement?
So we most often see "Potential" used to mean potential energy without telling us relative to where !.

We have to settle for measuring the work required to move a charge from somewhere that's accessible to somewhere else also accessible.
That work is equal to the difference in absolute potentials between those two points --
but we needn't go clear out to infinity to measure it , just from one point to the other.
Aha - difference in absolute potentials is "Potential Difference" , the nom de plume of Voltage !
It has the units of work per unit charge, Volts = Joules/Coulomb.
Your car battery adds 12 joules(watt-seconds)of energy to every coulomb(ampere-second) of charge it delivers.
The distance is only a few inches - there's no need to go to infinity to measure it.

That is how i think 'intellectually' of voltage. But I'm not very intellectual...That's why voltmeters have two leads , and they work well despite neither lead being long enough to reach very far.
If you had a voltmeter with one test lead a quarter of a million miles long, you could measure the voltage between Earth and moon.
They've already measured the local fields there:
http://meetingorganizer.copernicus.org/EPSC2013/EPSC2013-578-2.pdf

1. Introduction
The electrostatic potential between the Moon surface and space is a key parameter that is fundamental for lunar science and human exploration on the Moon.
Many investigations of electric potential and associated electric fields have been conducted theoretically and experimentally from the surface and orbits using solar wind plasma since the Apollo era...
In summary,
high energy electron flux results in -400 V potential in the nightside of the Moon.
In the dayside, due to the photoelectron emission the surface tend to charge positively with +5–+20 V, while near the magnetic anomaly, potential more than +100 V is expected.

have fun - old jim

 

[tubeswell]

What's mica?

a silicate mineral, used for a variety of purposes including; electrical insulation, and in the production of some capacitors (i.e.; silvered mica capacitors)

 

[jeffery_winkle]

A Josephson junction consists of two superconductors separated by a thin barrier. Microwave radiation causes a quantized DC voltage to form across the junction in steps of V=f/K, where f is the microwave frequency, and K = 2e/h is the Josephson constant. A quantum voltage standard is then constructed from a series of Josephson junctions.