Newbie question regarding understanding of voltage

recca02

Joined Apr 2, 2007
1,214
I know that voltage cannot be "used up", but it seems like it would work that way because if you have a lot of voltage drops and then something at the end of your circuit requiring a lot of voltage, there wouldn't be enough voltage left...?
u are correct, if u require to run a device requiring say 240 volts supply and if u wire it in such a fashion that a lot of voltage was dropped across the wire and some other element/device in series with this device the device wont run atleast not as per ratings since it is not getting rated voltage.

edit: (ignore this part if this is not what u wanted to know)
however there will always be a voltage across anything connected in a loop with a source
ranging from 0 to the source voltage depending on the resistance of components connected in series with it.
 

Thread Starter

sofakng

Joined Oct 30, 2007
19
OK... I think I understand, but let me just ask one last question...

Can somebody rephrase the following statement? (from the book)
Because it takes energy to force electrons to flow against the opposition of a resistance, there will be voltage manifested (or "dropped") between any points in a circuit with resistance between them.
How is the author using the word "manifest"? It means "to show", so it seems like the above would mean: "...there will be voltage shown between any points in a circuit with resistance between them."

Although, the word "dropped" in the above quotation would also seem like the author might mean: "...there will be lowered voltage between any points in a circuit with resistance between them."
 

jpitz31

Joined Oct 24, 2007
37
Manifest in this case indicates that voltage will appear across the component.
Yes the voltage will be less that the source voltage. How much depends what other resistances are in the circuit with the source voltage.

See calculation for resistance in a series circuit. Related to Ohms law.

Thanks

Joe
 

recca02

Joined Apr 2, 2007
1,214
so it seems like the above would mean: "...there will be voltage shown between any points in a circuit with resistance between them."
exactly like Mr. jpitz suggested take a voltmeter and u will be shown a voltage at those two points.
why?
because those two points are at different voltages had there been no resistance between those two points no loss of voltage wud have been there and no voltage difference wud have been detected by voltmeter (remember voltage is a relative term like height).

btw feel free to post whatever doubt u have.
 

Dave

Joined Nov 17, 2003
6,970
How is the author using the word "manifest"? It means "to show", so it seems like the above would mean: "...there will be voltage shown between any points in a circuit with resistance between them."
In he context of this section of the e-book the word "manifested" is termed to mean becomes apparent or created.

Dave
 

niftydog

Joined Jun 13, 2007
95
Chicken before the egg? Maybe. I learned "egg before chicken." :D
Well, chickens can't exist without eggs and vice versa. However you look at it, the result is the same. I figure it's easy to see how a battery can create a voltage without requiring current flow. But for the lamp it's easier (for me) to visualise the flowing current creating a voltage. Horses for courses! :D

Moving electrons through a resistance creates a voltage. However, voltage is required to move the electroncs in the first place!

If a battery provides voltage (eg. creates it) and voltage is created by moving current through a resistance, wouldn't they be added together? (eg. battery creates 9V and moving current through a lightbulb creates 1V so we now have 10V?)
This is why I tried to differentiate between a power source and something that consumes power like a lamp. Batteries create the energy that pushes the current around the circuit, and the lamp uses up that energy, so the battery is adding while the lamp is subtracting.

But it's really as simple as keeping this in mind: one terminal of the lamp is directly connected to the batteries positive terminal, so it simply HAS to be at the same voltage as that terminal. Likewise for the other terminal - it's directly connected to the 0V terminal, so it HAS to be at 0V as well. So, the whole 9V of the battery is also across the lamp. The battery adds, the lamp subtracts.

(Ignore the minuscule effect of the wire resistance, it's rarely taken into account in simple circuits.)

When the circuit get more complex, then the components that consume the power will share the total power available, but no matter how many components you have, the voltage provided by the battery will ALWAYS be balanced by the voltage drops across the components.

The word "drop" is simply a way of indicating that the voltage is being subtracted from the power source. For instance, one wouldn't say that the battery has a 9V drop across it because it's not consuming power, it's creating it. If anything, the battery has a 9V rise across it!
 

thingmaker3

Joined May 16, 2005
5,084
Batteries create the energy that pushes the current around the circuit, and the lamp uses up that energy, so the battery is adding while the lamp is subtracting.
I don't mean to nitpick, but I think it important be precise in our terms when dealing with this stuff. The battery doesn't create energy, but rather force. Electromotive force, to be extra nitpicky. The load resists this force.

The word "drop" is simply a way of indicating that the voltage is being subtracted from the power source.
That's a very good way of stating it!
 

Thread Starter

sofakng

Joined Oct 30, 2007
19
In he context of this section of the e-book the word "manifested" is termed to mean becomes apparent or created.
That is what is/was confusing me though... From what everybody is saying here, the voltage is NOT created anywhere except from the battery... right?

Are you saying that:

Because it takes energy to force electrons to flow against the opposition of a resistance, there will be voltage manifested (or "dropped") between any points in a circuit with resistance between them.
...really means, "there will be voltage created between any points in a circuit with resistance between them." ? (eg. I'm just substituting the word manifest for created since that is what you are saying it means)
 

cheddy

Joined Oct 19, 2007
87
I always thought that the voltage drop was an analogy to the release of potential energy, such as when you drop a rock you are releasing the potential energy of it and when you connect a circuit to a potential voltage you are releasing it's potential.
 

recca02

Joined Apr 2, 2007
1,214
since two voltages exist at the two points of resistance its fair to say a voltage is created
had there been no resistance no diff in voltage wud have been there and a voltage(difference -remember voltage is relative term) wud not show up on youre voltmeter across these two points.

though i find emf more convenient to understand as force it is an energy it is actually a misnomer and the units of emf more closely represent that of and energy.
 

chesart1

Joined Jan 23, 2006
269
I really appriciate all of the help... I don't understand why I just can't grasp this concept! (I can graduate from college with a four year degree, but have trouble understanding the simple [?] concept of voltage?!)

Would I be correct in saying that a battery generates 9 volts and each component with resistance uses up (eg. see niftydogs comment) part of that voltage? Correct

It makes sense to me that if we start with 9v and 0.1v is required to push electrons through a resistance (eg. a battery). It also makes sense to me that to push electrons through any resistance it will require more and more voltage. (eg. a larger resistor would require more voltage to achieve the same rate of current?) Correct

I guess I'm just not comprehending the whole "drop" terminology :)

I'll have to re-read the beginning of the book on this site (and the posts from this thread) and try really hard to picture what is going on...

EDIT: I also think that using the term "drop" was a bad idea :)
The term "drop" refers to the difference in voltage on each side of a component with respect to ground. If the measure voltage on one side of the light bulb is 9 volts and the measured voltage on the other side of the light bulb is 0 volts than the voltage drop from one side of the bulb to the other side is 9 volts.
 

niftydog

Joined Jun 13, 2007
95
..."there will be voltage created between any points in a circuit with resistance between them." ? (eg. I'm just substituting the word manifest for created since that is what you are saying it means)
manifest = apparent, evident, perceived etc. Subbing the word "created" does make sense to those who understand the intent of the sentence, but it's not necessarily completely accurate.

What you must grasp is that voltage is just a means of relating current and resistance. So, while the voltage in the lamp is, in a sense, "created" (by the current flow) it is not contributing volts to the circuit, it is just an indication that the lamp has current flowing through it.

The other way of putting this is "there will be a voltage developed..."

But it sounds like you're on the right track. A battery is a voltage source - it contributes voltage to a circuit - whilst most components just use the voltage to do what they're designed to do.
 

Thread Starter

sofakng

Joined Oct 30, 2007
19
What does this statement mean (regarding a break inside a circuit):

As before, with no flow of electrons, the entire potential (voltage) of the battery is available across the break
 

recca02

Joined Apr 2, 2007
1,214
with no flow of electron no voltage is dropped across any component and if u measure the voltage across the break the entire voltage is shown at the two points.
however things change drastically if the break is shorted and current is established in the loop the current drops voltages across resistances in this case.

its like if u touch a high potential end your entire body is raised to that potential and unless u complete the circuit in some way no current can flow thru u thus no energy is wasted (or voltage is dropped on u). BTW do not try this experiment.
 

Thread Starter

sofakng

Joined Oct 30, 2007
19
Ahhh... that makes sense. No voltage is dropped so the full voltage is "still available" (eg. it encounters no resistance)
 
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