Understanding Electric Currents in Fig 5.13 & 5.14(b)

In summary: doesn't exist in reality anymore? or it exists but in a different form? please help me understand this.in fig 5.14b the 'ground symbol' is included. this tells us that the terminals of both batteries are at the same potential. right. so why is there a ground symbol? is it necessary?...or again, is it just there for the benefit of the diagram?please help me to understand this.thanks
  • #1
PainterGuy
940
69
hello,

this is a pdf from a book:--
https://docs.google.com/viewer?a=v&...ljZmItY2UyYzFjZTllMzM0&hl=en&authkey=CNeg85sN

in fig 5.13 12v supply and 8v supply are connected to each other. perhaps the ground symbol tells us that the terminals of both batteries are at the same potential. I'm not sure. in "reality" this is going to cause a problem. the electric current which is "actual" current would start flowing from 12v supply toward 8v supply because electrons at negative terminal of 12v battery have more potential (12v/coulomb) than that of 8v battery. so what does this really mean? please help me to understand this.

in fig 5.14(b) what is reason for including ground symbol? to me this is pointless. there was no need.any reason for its inclusion. please show me the way.

cheers
 
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  • #2
First, hooking the supplies together like in fig 5.13 will not cause any problems at all, as long as the other ends aren't hooked together by a wirealso.

Because the negative terminals are hooked together, they are at the same potential as each other. It's the other ends that are different.

The ground symbol serves as a voltage reference point. Whenever you measure voltage, it has to be between two points. You measure it across a resister, across the two terminals of a battery, or otherwise between any two points.

Voltages are usually given with two points, such as: Vba = 4V. If you are given a voltage with only one point, then it is implied that the other point is ground, indicated by the ground symbol on the circuit.

Va = 12V
Vb = 8V
 
  • #3
thanks, Jiggy-Ninja.

one small question:--- is circuit in reality also grounded? or is it only on diagrams? all help is welcome.
 
  • #4
This is for the circuit analysis purposes. In real life, very rarely does anyone put batteries in a circuit in opposition to each other.
 
  • #5
painterguy said:
thanks, Jiggy-Ninja.

one small question:--- is circuit in reality also grounded? or is it only on diagrams? all help is welcome.
You mean Earth ground? I think that has a different symbol.
 
  • #6
Have a care with this book.

Firstly Boylestadt continues the modern trend to take starship Kirchoff where no scientist ever intended.

He offers you the Man's original version of the loop law in 5.9. If you use this one you will never be wrong.

However he also says the book will use an extended version as in 5.8. This version can lead to difficulties as Professor Lewin of MIT so ably demonstrates on Utube and has been so hotly debated here several times.

As regards to the earthing of the common negative terminal. This is necessary to give credence to the statement that Kirchoff's loop law can be applied without a complete loop. If you cannot guarantee that both negative terminals are at the same potential, the rest of the argument is suspect.
 
  • #7
Studiot said:
Have a care with this book.

Firstly Boylestadt continues the modern trend to take starship Kirchoff where no scientist ever intended.

He offers you the Man's original version of the loop law in 5.9. If you use this one you will never be wrong.

However he also says the book will use an extended version as in 5.8. This version can lead to difficulties as Professor Lewin of MIT so ably demonstrates on Utube and has been so hotly debated here several times.

As regards to the earthing of the common negative terminal. This is necessary to give credence to the statement that Kirchoff's loop law can be applied without a complete loop. If you cannot guarantee that both negative terminals are at the same potential, the rest of the argument is suspect.

a lot of thanks, Studiot. how did you know it was from Boylestadt?? did you used this book?
who Man in "Man's orignal version"? much appreciates your assistance.

cheers
 
  • #8
In this thread Kirchoff = The Man.

I read your link before commenting! Boylestadt was written at the top.
 
  • #9
Studiot said:
In this thread Kirchoff = The Man.

I read your link before commenting! Boylestadt was written at the top.


i see. thanks for reply.

cheers
 
  • #10
hello everyone,

i'm still struggling with this concept. okay. as you say ground symbol is there as a voltage reference point and is only drawn in circuit analysis diagrams.

please open the google doc in my first post in this thread.

in fig 5.14a there are two batteries 16 E1 and E2. take the case of E1. every person knows that +ve terminal is at higher potential and -ve is at zero potential. right. so when i read 16v E1 i take it that E1's +ive is at 16v potential with reference to its own -ve terminal which is at zero potential. so using an extra reference symbole (which is 'ground symbol' at zero potential) make not sense. it will be redundancy.

the same reasoning is for true for R2 in the same fig 5.14a. R2 reads 4.2v. i understand it that potential difference across R2 is 4.2v. which to me means while traversing R2 4.2v was lost and this 4.2v p.d. uses zero potential terminal of E1 as a reference.

i know I'm going wrong somewhere or everywhere. please fill in the gaps in my understanding. every help is appreciated.

cheers
 
  • #11
painterguy said:
hello everyone,

i'm still struggling with this concept. okay. as you say ground symbol is there as a voltage reference point and is only drawn in circuit analysis diagrams.

please open the google doc in my first post in this thread.

in fig 5.14a there are two batteries 16 E1 and E2. take the case of E1. every person knows that +ve terminal is at higher potential and -ve is at zero potential. right. so when i read 16v E1 i take it that E1's +ive is at 16v potential with reference to its own -ve terminal which is at zero potential. so using an extra reference symbole (which is 'ground symbol' at zero potential) make not sense. it will be redundancy.

the same reasoning is for true for R2 in the same fig 5.14a. R2 reads 4.2v. i understand it that potential difference across R2 is 4.2v. which to me means while traversing R2 4.2v was lost and this 4.2v p.d. uses zero potential terminal of E1 as a reference.

i know I'm going wrong somewhere or everywhere. please fill in the gaps in my understanding. every help is appreciated.

cheers
-ve isn't always at 0V. In fig 5.14a it is, because it's attached to the ground symbol. However, that isn't always the case.

Consider two 5V batteries connected together in series. The - terminal of V1 is at 0V, therefore the + terminal is at +5V. However, the - terminal of V2 is not at 0V. Because it is attached to the + terminal of V1, it is at +5V. Therefore, the + terminal is 5V above that, at +10V.

The + terminal of V2 is 5V higher than its - terminal, but because it's "on top of" V1 (so to speak), it's 10V higher than ground.

It might seem unnecessary in a simple circuit like this, but when the circuits start getting more complex and with multiple power sources (such as op amps that need +/- voltage supplies), keeping track of ground becomes very important.

It's not really redundant in this case, it's just not necessary to illustrate what the text is trying to show.

And your reasoning for R2 is incorrect. Remember that voltage is always measured between two points. When measuring across a resistor, you already have two points: one end of the resistor to the other. You don't need the 0V ground reference for that.

Where ground comes in is when you are asked to measure the voltage and only given one point to measure at. The other point is implied to be ground. That's what the ground marking it for.

Since you're not really doing anything like that for these examples, the ground mark isn't really necessary in these diagrams.
 
  • #12
Jiggy-Ninja me very grateful to you for this teaching to me. many many thanks. me will post again in case there is problem.

cheers
 
  • #13
okay, here i am again requesting you to help me.:smile:

1:-- on a circuit diagram ground symbols are like water tanks. all tanks having water at the same level so that connecting the tanks does not make the water flow one tank to another. is ground symbols always taken to be at 0V?

2:-- in case of a battery negative terminal is taken to be at 0V, hence it is a ground in itself. but in the case of AC current, can we use 'circuit' ground symbols? AC only stays at 0V. i mea it cross 0V points twice if we start measuring the cycle from the one peak to next peak. perhaps in case of AC 'circuit' ground symbols mean that voltage and polarity there will be the same no matter what.

tell me please. many thanks.

cheers:smile:
 
  • #14
painterguy said:
okay, here i am again requesting you to help me.:smile:

1:-- on a circuit diagram ground symbols are like water tanks. all tanks having water at the same level so that connecting the tanks does not make the water flow one tank to another. is ground symbols always taken to be at 0V?

2:-- in case of a battery negative terminal is taken to be at 0V, hence it is a ground in itself. but in the case of AC current, can we use 'circuit' ground symbols? AC only stays at 0V. i mea it cross 0V points twice if we start measuring the cycle from the one peak to next peak. perhaps in case of AC 'circuit' ground symbols mean that voltage and polarity there will be the same no matter what.

tell me please. many thanks.

cheers:smile:

some one please help me with this. some commentary please. some idea!:cry:

cheers:smile:
 
  • #15
I don't like using the "water analogy" for circuit analysis, but it can be a learning tool. Take a look at the link below about this:

watdc.gif


http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html" [Broken]
 

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  • #16
painterguy said:
okay, here i am again requesting you to help me.:smile:

1:-- on a circuit diagram ground symbols are like water tanks. all tanks having water at the same level so that connecting the tanks does not make the water flow one tank to another. is ground symbols always taken to be at 0V?

2:-- in case of a battery negative terminal is taken to be at 0V, hence it is a ground in itself. but in the case of AC current, can we use 'circuit' ground symbols? AC only stays at 0V. i mea it cross 0V points twice if we start measuring the cycle from the one peak to next peak. perhaps in case of AC 'circuit' ground symbols mean that voltage and polarity there will be the same no matter what.

tell me please. many thanks.

cheers:smile:

1) Not really sure where you're going with the tank analogy (as another guy mentioned,analogies can be misleading if you abuse them too much), but ground is always 0V. That's pretty much how it's defined. Ground is the point that you measure all the other voltages in the circuit relative to, so measuring ground with respect to itself should give you a 0V measurement. if you don't get 0V, you have a problem with either your circuit or your measuring equipment.

In more complicated circuits, you might have multiple different grounds (such as analog and digital grounds) that are kept separate from each other, but are considered 0V for each of their respective circuits.

2) The negative terminal is NOT ground. The ground symbol is ground. The negative terminal is usually the one hooked to ground because only by convention to keep the voltages positive. If the source was flipped and the positive end hooked to ground, the math would still work out the same (as long as any polarized components were reversed too).

Op amps, in fact, have to have both a positive and a negative voltage supply in order to work properly. This is commonly done by using two voltage sources. One with the negative end hooked to ground (to give you the positive supply) and the other with the positive end grounded (to give you the negative voltage).
 

1. What is an electric current?

An electric current is the flow of electric charge through a conducting material, such as a wire or circuit. It is measured in units of amperes (A) and is often represented by the symbol "I".

2. How is electric current measured?

Electric current is measured using a device called an ammeter, which is connected in series with the circuit. The ammeter measures the amount of charge passing through a specific point in the circuit per unit time, giving the current value.

3. What causes electric current to flow?

Electric current is caused by the movement of electrons. In a circuit, electrons flow from the negative terminal of a power source (such as a battery) to the positive terminal, creating a continuous flow of electric charge.

4. What is the difference between AC and DC currents?

AC (alternating current) and DC (direct current) are two types of electric currents. AC currents constantly change direction, while DC currents flow in one direction. AC currents are typically used for powering large-scale electrical grids, while DC currents are used in smaller devices such as batteries and electronic circuits.

5. How does resistance affect electric currents?

Resistance is the measure of a material's ability to resist the flow of electric current. Higher resistance means that it is more difficult for electric current to flow through a material. This can lead to a decrease in the overall current in a circuit, as well as the generation of heat. Resistance is often represented by the symbol "R" and is measured in units of ohms (Ω).

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