Ground Is Always Considered At 0 Volt?

"Shields up! Evasive manoeuvres!"

You need a change in potential to get current flow.

1- because it is considered (of course you may consider it to be a hundred volt too and bias everything as such)

2- It depends, I could make it in several ways.

The Opposive sources are get cancelled each other..

i.e., -5+5=0 Volt

You can see it, according to electric circuit analysis , the current flow will exist only there, if there is any potential difference exists..

But here, Net potential=0 volt

So, current does not flow.. Lamp will not glow.. At the same time, your shown diagram is not correct as per your question.. you should connect both two negative terminals of the two sources as per your question...

Now, i think you got clear..

Satisfied..?!

The voltage across the bulb will be 0V from the two batteries. However, depending on what type of a lamp you have, a good illusionist can make this lamp glow.

"Go to Yellow Alert!"

http://www.kidslovekits.com/projects/KITSEC/index.html

Where is the ground? It is not easily visible in your image.

In the battery, the positive and negative polarities are relative concepts. The electrolyte material in the battery produces a potential whereas one pole is more negative than the other... the potential is determined by thermodynamics, or more specifically statistical mechanics.

http://www.tumblr.com/tagged/how+do+zinc+carbon+batteries+work

Might have gone over someones head.

Yawp.

^{Probably mine...}

and if one source offers 5 volt and other offers 15 volt ? will bulb glow?
because now there is a potential difference as it's called voltages!

You're having a terminology issue here. The negative and positive potential of a supply voltage can be anything. The negative for instance can be 1000 volts, and the positive can be 1010 volts. You now have a 10 volt supply. The 1000 volt negative is only called ground relative to anything tied directly to it. It is obviously not true ground.

so you mean that ground could be at 100v it's not necessary for us to say ground where voltages are 0v.

A 100 volt "ground" is ONLY called ground relative to what is tied directly to it. It is not true ground. Better terminology would be to call your 100 volt ground "power supply negative" instead of ground.

If you have a circuit board with multiple voltage supplies (and most do), you would only call the lowest potential on the board ground. I would not personally even call THAT ground.

When you carry out anything you have to take a reference frame and assume it to be same everywhere isn't it?

When you say measure speed of a car - you take earth as stationary (which it isn't) and emasure with reference to it and say it is at 100KMPH but with respect to another car (which is at 80KMPH with ref to earth) it is only 20 KMPH (or may be even 180 KMPH) depending on their relative direction.

To make all this measurement standard we take the earth (assume it to be stationary) and measure with reference to it isn't it?

To emasure the height of a structure say a mountain we measure from MSL (which again isn't constant but is almost so and treated to be one)

Do you see the concept? To measure the quantity - we need a reference frame large enough that doesn't vary across the total work-domain significantly so that the results are duplicateable and a bit standardised.

For electrical systems too we take the earth as reference and measure the potentials with respect to it and call it to be at zero potential (just since measurement scale starts at zero as in earlier case - for speed earth speed is zero, for height MSL elevation is zero). This si fortunate since earth is electrically conductive. (Look at the thermal point of view - we can not take then the earth temperature as zero and have to have other means for measurement)

Now any conducting media at contact with earth would come at earth potential (and at so called zero potential) - this includes human body too.

Any electrical circuit the driving force is the nett potential (look at KVL) and that is withinn a closed circuit, irrespective of whether a particular pole is earthed or not. In case of a pole is earthed, the other edge would be at 0+ the Electro motive force of the source, if it isn't it could be at any voltage (called a floating system instead of an earthed). This floating system (being at indeterminate voltage with respect to ground) may be some times dangerous (not in small cells etc in your drawing of course) and may be able to even kill (I have heard about fire/explosions in petrol stations due to static earthings though didn't investigate the truth but is possible though not probable).

This is the reason why the systems are earthed on one end so that the potential of the system with ref to ground zero is same every where.

_{I am not sure if I could make it clear or confused you more.}

Go easy on otomanb, he's discovering on his own one of the fundamental ideas for anayzing linear systems, superposition. (I'm surprised, for once the hyperphysics link is inferior to Wikipedia.)

There are several key terms in the definition that I linked. The most commonly overlooked rule to apply this method is that the sources must be fully independent to be removed in analysis. Since the two batteries are seperate independant voltage sources, you replace one battery with a short circuit or more accurately change the voltage drop for one battery to 0V and analyze the current (I1) through your load (lamp). Next you repeat the analysis with the other battery at 0V and the original battery voltage at normal value. The anaysis then produces a new current (I2)through your load. The actual final current through your load is then I=I1+I2.

Now often it is tricky in more complicated circuitry to identify which power sources are independent sources. The rule though is that if you can change one source without automatically changing the other source, they are independent. otomanb changed one battery from 5 to 15 volts without having to change the other battery. Their independent DC sources.

Ground being defined as being at 0 Volts is just convenient and perhaps just a little bit safer. With one side of all circuits tied to ground, we know what portions of a circuit are dangerous to touch while our bodies are touching the ground. Describing voltages, relative to the ground, as being 'hot', high', or positive is just a convention that we decided to adopt. Take the example of automobiles. "Prior to the 12-volt changeover in '53-'56, the majority of American vehicles were Positive-Ground. MoPar, Ford/Merc/Lincoln, Caddy & La Salle, GMC, Packard, Nash, Hudson, Pierce, Studebaker were all positive-ground.

Major exceptions were: Buick, Chevy, Olds, Pontiac."

If the negative posts of the two batteries are connected together in your diagram, there would be a complete circuit, however the lamp would not light. The algebracic sum of all the voltages in the circuit equals zero 5 + (-5) = 0 If you changed one of the batteries to be 15 V then current would flow and the lamp would light up.

Your diagram has no visible reference to ground. For your circuit to be 'related' to ground, some part of it would have to be connected to ground.

Put another way: "Every description of events in space involves the use of a rigid body to which such events have to be referred.....Let us suppose our old friend the railway carriage to be travelling........"

got that one thank you