Potential at a point in a circuit

In summary: Since the charge moves from high to low potential, the potential decreases as the charge moves, so the potential difference is measured in the opposite direction: ie we use a positive charge (ie not an electron), and so it will flow outside the battery from the long line (+ve) to the short line (-ve), and the potential will be highest at the long line, and decrease to zero at the short line
  • #1
vadevalor
35
0
ImageUploadedByTapatalk1379582898.613208.jpg


Why is the potential at X , denoted by V, not

V/8 = 4.8/(4.8+7.6) ? Why is numerator of resistance part 7.6 and not 4.8 by potential divider principle?
 
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  • #2
hi vadevalor! :smile:

conventionally, the current flows from the positive terminal (long line) to the negative terminal (short line)

(the electrons, of course go the other way, towards the positive!)

so the short line is at zero potential, and you have to start from the short line to get to X to find the potential at X, ie the potential difference from zero

(see eg "Electric Potential Diagrams" at http://www.physicsclassroom.com/class/circuits/u9l1c.cfm)

ie you go through the 7.6Ω, so 7.6 is in the numerator :wink:
 
  • #3
The values 4.8V and 1.6V shown on the circuit diagram are misleading. Should not the unit be Ω instead of V?

The equivalent circuit is a voltage supply of 8V connected to 4.8Ω in series with 7.6Ω as shown correctly in your diagram.

Hence 8V is the voltage on (4.8 + 7.6)Ω.

And the voltage on 4.8Ω can be found be using direct proportion.
 
  • #4
Thank you all for your inputs! I realized its the direction after thinking for so long. And yea it should be ohm instead of v.

I have another question regarding potential could you guys help me? Answer is A but i don't understand the solution as there are 'conflicting battery direction' and i don't know how to start

ImageUploadedByTapatalk1379591023.772679.jpg


Thanks!
- curious lost soul
 
  • #5
hi vadevalor! :smile:
vadevalor said:
Answer is A but i don't understand the solution as there are 'conflicting battery direction' and i don't know how to start

start by replacing the three batteries by one 3V battery …

what is the potential at Y? and where is that measured from?

and now adjust that to start from X instead :wink:
 
  • #6
tiny-tim said:
hi vadevalor! :smile:start by replacing the three batteries by one 3V battery …

what is the potential at Y? and where is that measured from?

and now adjust that to start from X instead :wink:

Should i put the 3v battery to the right or left of X and should i go from + terminal to -terminal from X to Y like current flow or electron flow?

Smiles :D
 
  • #7
hi vadevalor! :smile:
vadevalor said:
Should i put the 3v battery to the right or left of X and should i go from + terminal to -terminal from X to Y like current flow or electron flow?

Smiles :D

you must always always ALWAYS use current flow not electron flow!

X is somewhere in the middle of the 3V battery, isn't it? :wink:
 
  • #8
tiny-tim said:
hi vadevalor! :smile:you must always always ALWAYS use current flow not electron flow!

X is somewhere in the middle of the 3V battery, isn't it? :wink:

ImageUploadedByTapatalk1379593167.784346.jpg


Think i got it! Yes! So its 2-1.5= 0.5v following current direction. But when do i know to use current or electron flow direction? Above for potential divider i was told to look at electron flow
 
  • #9
yes, i like your diagram …

you've split the batteries into two: a 2V and a 2 minus 1 = 1V battery going the same way,

so it's easy to see whether to add or subtract :smile:
vadevalor said:
Above for potential divider i was told to look at electron flow

i don't understand that :redface:

it's always current flow​

what exactly did they say? :confused:
 
  • #10
tiny-tim said:
hi vadevalor! :smile:

conventionally, the current flows from the positive terminal (long line) to the negative terminal (short line)

(the electrons, of course go the other way, towards the positive!)

so the short line is at zero potential, and you have to start from the short line to get to X to find the potential at X, ie the potential difference from zero

(see eg "Electric Potential Diagrams" at http://www.physicsclassroom.com/class/circuits/u9l1c.cfm)

ie you go through the 7.6Ω, so 7.6 is in the numerator :wink:

Its the third paragraph from your first answer :) starting from the short line (electron flow direction)
 
  • #11
vadevalor said:
Its the third paragraph from your first answer :) starting from the short line (electron flow direction)

ah, i see, you're interpreting the flow direction as the direction for measuring the potential

no, the flow direction (= the current direction) is the direction the charge is moving (which we assume is a positive charge, so the opposite of the electron flow direction)

since the charge moves from high to low potential, the potential decreases as the charge moves, so the potential difference is measured in the opposite direction:

ie we use a positive charge (ie not an electron), and so it will flow outside the battery from the long line (+ve) to the short line (-ve), and the potential will be highest at the long line, and decrease to zero at the short line :wink:
 

1. What is potential at a point in a circuit?

The potential at a point in a circuit refers to the electric potential energy per unit charge at that specific point. It is measured in volts (V) and is a measure of the amount of work needed to move a unit charge from one point to another within the circuit.

2. How is potential at a point in a circuit calculated?

The potential at a point in a circuit is calculated by dividing the electric potential energy at that point by the amount of charge present. This can be represented by the equation V = U/Q, where V is the potential, U is the potential energy, and Q is the charge.

3. What factors affect the potential at a point in a circuit?

The potential at a point in a circuit is affected by the amount of charge present, the distance between the point and the source of the potential, and any components in the circuit that may influence the flow of charge.

4. Why is potential at a point in a circuit important?

The potential at a point in a circuit is important because it determines the direction and magnitude of the electric field at that point. It also allows us to calculate the amount of work needed to move a charge within the circuit and can help us understand the behavior of components in the circuit.

5. How does potential at a point in a circuit relate to voltage?

The potential at a point in a circuit is essentially the same as the voltage at that point. Voltage is a measure of the potential difference between two points in the circuit, and the potential at a specific point is just the voltage at that point compared to a reference point. In other words, potential is a specific type of voltage measurement.

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