Energy Flow From Battery to the Light Bulb

[Dario56]

TL;DR Summary

How does energy flow from battery to the light bulb create electric field or potential difference on resistor?

When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor. Heat is eventually converted to electromagnetic radiation making light bulb shine. Light energy comes from flow of electrons and flow is created because of voltage which comes from the battery.

I saw an intersting video (science asylum on youtube) where it is said that voltage or energy powering a light bulb comes from fields around it.

When current flows in a conductor with a battery there are both electric and magnetic field in space around it because of which there must be flow of energy which magnitude and direction is determined by the Poynting vector. This also has sense.

However, how does energy flow coming from the battery to the light bulb create potential difference? What is a mechanism by which that happens? Surface charges create electric field in the conductor, but what does energy flow from battery to the light bulb given by the Poynting vector have to do with surface charges?

 

[anorlunda]

When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor.

Totally wrong.

The mechanism is described by Maxwell's Equations. The math is not the easiest, but the equations and principles are well proven. So if you want to understand, it will take more work than reading a 2 paragraph reply in this thread. Start studying here: https://en.wikipedia.org/wiki/Maxwell's_equations

Or in video form, this course from Yale is pretty easy to follow.

 

[A.T.]

We already have a current thread about this:
https://www.physicsforums.com/threa...om-veritasium-on-youtube.1009268/post-6566217

 

[anuttarasammyak]

I find this article very informative. http://amasci.com/elect/poynt/poynt.html

 

[jartsa]

However, how does energy flow coming from the battery to the light bulb create potential difference? What is a mechanism by which that happens? Surface charges create electric field in the conductor, but what does energy flow from battery to the light bulb given by the Poynting vector have to do with surface charges?

Let's say we have an empty box. Then electrons start flowing into the box. Now we have fields flowing into the box, and we have energy flowing into the box.

I'm just trying to answer the basic question of OP here. Which was about the relationship between energy and field.

Let's say those electrons are shot slowly along a very narrow tube into said box. Now, as we have learned, the energy flows outside of the tube. And there is also a electric field flowing outside of the tube. And there is a magnetic field outside of the tube that tells us that the electric field outside of the tube is flowing.

So now outside of our box there is an increasing electric field, and outside of the box there is an incresing amount of electric field energy.

 

[Dario56]

Totally wrong.

The mechanism is described by Maxwell's Equations. The math is not the easiest, but the equations and principles are well proven. So if you want to understand, it will take more work than reading a 2 paragraph reply in this thread. Start studying here: https://en.wikipedia.org/wiki/Maxwell's_equations

Or in video form, this course from Yale is pretty easy to follow.

Hmm, I wouldn't agree that is wrong. Here is my reference, section: microscopic description https://en.m.wikipedia.org/wiki/Joule_heating

Quote from wikipedia article:

Joule heating is caused by interactions between charge carriers (usually electrons) and the body of the conductor (usually atomic ions).

A voltage difference between two points of a conductor creates an electric field that accelerates charge carriers in the direction of the electric field, giving them kinetic energy. When the charged particles collide with ions in the conductor, the particles are scattered; their direction of motion becomes random rather than aligned with the electric field, which constitutes thermal motion. Thus, energy from the electrical field is converted into thermal energy.[3]

 

[Dario56]

I find this article very informative. http://amasci.com/elect/poynt/poynt.html

Thank you, it is a great article. I do understand that energy given by the battery is carried and transmitted by the fields. Poynting vector says that when we have both electric and magnetic field present at some point there must be flux of energy. However, what I am not clear is how does carried energy create potential differences inside of conductor necessary for creating current. Energy flows to circuit elements like a resistor, yes. But, how does this energy flow separate charges and create voltage?

 

[sophiecentaur]

Summary:: How does energy flow from battery to the light bulb create electric field or potential difference on resistor?

filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor.

Then electrons start flowing into the box. Now we have fields flowing into the box, and we have energy flowing into the box.

These two (and other) comments are mis-representing the role of electrons. The kinetic energy of an electron (even all of the electrons) is minute because the drift velocity through a conductor is a matter of mm's per second. It is the Fields and the work done to change the fields at each end of the circuit that constitutes the Energy Transfer. If you consider RF power (say 10MHz) flowing along a wire, the actual displacements and velocities of electrons, constantly changing direction with cycles of RF will be less than the sizes of the ions they are flowing through.
I like to think in terms of a bicycle chain which is a very small proportion of the total mass of bike and rider and the links are actually moving fairly slowly over the sprockets. Yet the legs of the cyclist transfer a lot of energy to the tyres in contact with the road via Forces and Movement. Any KE is not significant.

 

[anuttarasammyak]

However, what I am not clear is how does carried energy create potential differences inside of conductor necessary for creating current. Energy flows to circuit elements like a resistor, yes. But, how does this energy flow separate charges and create voltage?

A: Charged wire and current in it
B: Poynting vector energy flow
A is accompanied by B. B is accompanied by A. You seem to like to observe A causes B or B causes A. I am not sure causal relation is applicable here.

 

[sophiecentaur]

I am not sure causal relation is applicable here.

This can be a great stumbling block for some people. Every transfer of energy has a history to it. Someone raised the ball to the top floor window and the energy became KE, back at the ground - or did someone throw it from the ground in the first place? Current - volts - current - volts. chicken - egg - chicken - egg.
This seems to be a 'faith' thing.

 

[Dario56]

This can be a great stumbling block for some people. Every transfer of energy has a history to it. Someone raised the ball to the top floor window and the energy became KE, back at the ground - or did someone throw it from the ground in the first place? Current - volts - current - volts. chicken - egg - chicken - egg.
This seems to be a 'faith' thing.

Well, we can say that voltage causes current. It is a driving force for current in the same way temperature difference causea heat flux. It has no sense to say that current causes voltage or that heat flux causes temperature differences.

In my opinion, significance of the Poynting vector is that it clearly shows that battery is an energy source and that circuit elements use that energy, but it doesn't explain mechanism by which this energy is transmitted. It only shows direction of its flux and its magnitude.

As far as I know, surface charges create neccesary electric fields in the conductor, electric field of the battery causes charges of the conductor to accumulate on its surface initally. Battery initially accumulates charges on conductor surface which than create electric fields neccesary to make steady currents in circuit branches. So, battery provides neccesary energy (potential difference or electric field) to power circuit elements and Poynting vector can be used to calculate this power by intergtating its value over surface of the conductor and circuit elements if fields are known. This power must be $$ P = UI $$

 

[sophiecentaur]

It has no sense to say that current causes voltage

it clearly shows that battery is an energy source

If you use a battery as an energy source (and most of the time that's what we do use) then there's a logic that says in the short term, Volts cause things to happen. But even if there's just one example that uses a flow of current as the energy source then it does make sense. If a stream of ions from the Sun arrive on a resistor, floating in space, they (the energy source) will 'cause' a PD. If you further upstream and look for the 'original' energy source that produced the stream of ions, you would probably have to involve the Big Bang and that wasn't a 'battery'.
Cause and effect are 'local considerations', IMO.

 

[anuttarasammyak]

I draw sketches to explain what happens before and after switching on for battery capacitor circuit. I hope it is of your help.

So (additional) charging of condenser or glowing of light bulb in battery-light bulb circuit starts with time delay of $R/c$ after switching-on and grows gradually where R is space distance between switch and condenser/light bulb. Wire arrangements, e.g. straight, winding, zigzag, do not matter.

 

[sophiecentaur]

I draw sketches to explain what happens

What point are you trying to make here? When a battery is used as a source of Energy then it is a source of Energy.

 

[alan123hk]

If a stream of ions from the Sun arrive on a resistor, floating in space, they (the energy source) will 'cause' a PD. If you further upstream and look for the 'original' energy source that produced the stream of ions, you would probably have to involve the Big Bang

I like this interesting and very creative example.

 

[anuttarasammyak]

I would have liked to describe some details of :
how energy from battery has been stored in space around the circuit before switch-on,
how switch-on triggers flow of that energy, and,
how the effects or signal of switch-on propagate outward to sustain and enlarge the flow of energy.

I hope it would be of OP's interest on mechanism of energy flow.

When a battery is used as a source of Energy then it is a source of Energy.

Yes, with time delay of R/c where R is distance of switch and battery terminal, the battery starts supplying energy to fill out and more energy that once existed but have gone to capacitor/resistor.

 

[sophiecentaur]

I would have liked to describe some details of :
how energy from battery has been stored in space around the circuit before switch-on,
how switch-on triggers flow of that energy, and,
how the effects or signal of switch-on propagate outward to sustain and enlarge the flow of energy.

I hope it would be of OP's interest on mechanism of energy flow.Yes, with time delay of R/c where R is distance of switch and battery terminal, the battery starts supplying energy to fill out and more energy that once existed but have gone to capacitor/resistor.

Without the battery in circuit, there is no net energy imbalance in the circuit. It's only when the battery is connected up that the Potential in the battery causes flow of current and the re-arrangement of fields.
In that window of time, a 'cause' and an 'effect' can be identified. But there has been a suggestion that Volts would always have to be the cause. This is not really true.