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Single terminal of battery alone connected to earth. Answered

I took a 12 Volt battery and connected its positive terminal to one end of LED bulb with enough series protection resistor. Then i connected the other end of the LED bulb to earth (soil with moisture outside my house). I did not connect negative terminal of the battery to anything. I expected the bulb to glow. But it did not glow until i connect the negative terminal also to ground. While there is potential difference between earth and battery why dont current flow through bulb when i did not connect negative terminal to earth.

 I have attached the photo of the battery that i used.
 I am sure that LED's were working properly and battery had enough capacity to provide current.




Best Answer 6 years ago

"Ground" is generally a misunderstood term.

The difference in electrical potential exists between the positive and negative terminals of your battery. There is no inherent relationship between the (-) terminal of a power supply and "ground." Don't confuse the two. Connecting to (or labeling) the negative as such is merely the most common usage of ground.

Ground is simply a reference. It's perfectly acceptable to connect the positive battery terminal to ground. Connected in such a way, positive is the ground reference and the negative terminal of your battery is now -12 volts when compared to ground. But there is no difference in the potential between the two battery terminals.

Bipolar power supplies have the ground reference in the middle, between a positive and a negative supply (like +/-12V).

At one point early in the transistor revolution it was quite common that circuits built around PNP transistors had a positive ground. Most computer power supplies are bipolar, or include a negative voltage component.

There are two types of current. Conduction current and displacement current. Displacement current is a bit complicated, so leave it. Let us talk about conduction current, which is the "current" we usually talk about. For a current to flow between two points in any circuit, there should be potential difference between those points. Now if are only saying the word "potential". You should always mention the word "potential" with respect to WHICH point in the circuit. If I say point A is at 5V, it means that the point A is at 5V with respect to the circuit ground. Now this circuit ground is called reference point or just ground of a circuit. Voltage or potential at any point of the circuit, now will be defined/measure with respect to this reference point. We can use any point of our wish as reference/ground. We assume this reference point /ground is at 0V ALWAYS. Okay, so if you take a 5V battery, it means that the positive terminal of the battery is at +5V with respect to the -ve terminal of the battery. If I connect a Resistor across the battery terminals, current will flow due to the potential difference, cz +ve terminal is at +5V and the -ve terminal is at 0V and a closed loop is formed. Here we chose -ve terminal as our reference/ground. Now if you connect the +ve terminal of the battery to -- resistor-- to EARTH ( also known as earth ground) , current would have flown if there was potential difference between those points. There is a general WRONG assumption: that the +ve terminal is at +5V and earth is usually considered 0V potential and hence due to a 5-0 = +5V potential difference, a current will flow. WRONG ! Actually no current will flow at all, cz the potential difference is actually 0V !. Again, when we define a potential, we should be clear which is our reference point in the circuit. If you say, the positive terminal of the battery is at potential +5V, it means the reference you have used is actually the -ve terminal of the battery. So every potential or voltage of a point in the circuit, is defined with respect to it. So what is the potential of earth here? Is it 0V ? No cz it is not the reference point we are using ! Here Earth is at +5V with respect to the -ve terminal. You can check it using a voltmeter connected between earth and our reference point ie., the -ve terminal. This is similar to: connecting one end of the resistor to the +ve of the battery and leaving the other end open. The open terminal will always be at the same potential as the +ve terminal = +5V. Hence in our circuit, potential difference = 0 between the battery +ve and earth, and hence no current will flow. Now, when you connect the -ve terminal to earth, since earth is a perfect conductor, we can assume it as a simple wire connected to the -ve terminal of the battery. It means earth is at 0V now, earth is just like the reference point.Thus a closed loop is formed between the battery terminals via the resistor and earth and hence current will flow. Now in the same circuit, you can also assume earth to be the reference point, i;e earth is at 0V. Now we can never say that +ve terminal is at 5V cz we already saw that, the postive terminal of the battery is said to be +5V with respect to its -ve terminal only. So in this assumption scenario, both earth and +ve terminal are at 0V, which you can check using a voltmeter connected across earth and the +ve terminal. So, potential difference is 0 and no current will flow. Now you can clarify your doubt regarding connecting two batteries to ground by yourself using this concept. I know it is a bit confusing :D , always be clear about the reference point in a circuit when we deal with voltages/potential. In summary: we can never say earth is at 0V unless you make it the reference point in our circuit. This is a basic mistake everybody makes. Always use the potential difference methodology to check if current flows. Closed loop methodology can sometimes mislead you if you have not understood it completely. eg: In a balanced wheaston bridge, no current flow through the middle resistor, even though it is a closed loop through the resistor.

Because without connecting the negative terminal of the battery, you had an open circuit. If you don't know what "open circuit" means, please visit your local information resource facility and find out. We aren't here to do your homework for you.

Try to learn how to communicate with people from Frollard.

^will probably be taken off youtube soon for copyright infringment; but its the electricity episode.

From about 2 minutes onward you see why a circuit is important.

**while there is a potential difference between the terminals on the battery, there is no potential difference between just one of the terminals and some other arbitrary object like 'ground'. That would be static electricity. in order to have AC or DC it really wants a circuit. (***most*** of the time)

Thank you for replying properly.

If that is so then what about this case? I will connect positive terminal of 12 v battery to ground (negative terminal will not be connected) and then positive terminal of 6 volt battery to the ground and in this case also i wont connect negative terminal of the battery. While there is potential difference of 6 v between both positive terminals of battery, will it be like there is no potential difference between one terminal of each battery and earth?

It is like saying a=b=a, but a is not equal to c.

Please help me

Again, without a circuit, there is no potential difference.

Batteries in a very rudimentary form act as an electron pump, it needs an input and an output -- otherwise it does no work.

if you had

{not connected)---A---battery++++ ground ++++battery---B----(not connected) between

assuming ground is conductive in this case
testing between A and B you would have a circuit (through the tester) and since the batteries are parallel (positive to positive) would be battery1 minus battery2 voltage (which they generally don't like).

Nice 1993 Vid, I met Bill Nye that scientific guy in New Orleans years ago.
Thanks for posting it :-)

He is my hero. My goal is to meet him before either of us kicks the bucket!