# EMF and potential in a circuit

• Krushnaraj Pandya
In summary, the conversation discusses the potential difference across ab and ac in a circuit with four identical cells connected in series. The correct answer for the potential difference across ab is E/2, which may initially seem confusing due to the sign of the EMF. However, this is due to the relative reference point chosen for measuring the EMF.
Krushnaraj Pandya
Gold Member

## Homework Statement

Four identical cells each having emf E and internal resistance r are connected in series to form a loop abcd as shown in figure (picture 1). Find potential difference across ab and ac.

2. Homework Equations

V=IR
equations for combination of cells and resistances

## The Attempt at a Solution

this is the circuit diagram-(picture 2. left for across ab and right one for across ac), I can find equivalent resistance easily, what confuses me is the sign of the emf- for ab three cells are sending current in one direction while one is in the opposite direction. So using +E for three and -E for one I get the answer -E/2 across ab but the correct answer is E/2. I think there's a fundamental mistake in my understanding of emf so I'd be grateful if someone can explain it to me in an simple, intuitive way. Thank you.

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Krushnaraj Pandya said:

## Homework Statement

Four identical cells each having emf E and internal resistance r are connected in series to form a loop abcd as shown in figure (picture 1). Find potential difference across ab and ac.

2. Homework Equations

V=IR
equations for combination of cells and resistances

## The Attempt at a Solution

this is the circuit diagram-(picture 2. left for across ab and right one for across ac), I can find equivalent resistance easily, what confuses me is the sign of the emf- for ab three cells are sending current in one direction while one is in the opposite direction. So using +E for three and -E for one I get the answer -E/2 across ab but the correct answer is E/2. I think there's a fundamental mistake in my understanding of emf so I'd be grateful if someone can explain it to me in an simple, intuitive way. Thank you.
I think the only thing you are missing is the idea that you have to measure the EMF relative to a reference. If you measure the EMF at ##b## relative to ##a## you get one sign. If you measure the EMF at ##a## relative to ##b##, you get the other sign.

tnich said:
I think the only thing you are missing is the idea that you have to measure the EMF relative to a reference. If you measure the EMF at ##b## relative to ##a## you get one sign. If you measure the EMF at ##a## relative to ##b##, you get the other sign.
Got it after some thinking, thank you :D

## 1. What is EMF in a circuit?

EMF stands for electromotive force and refers to the energy that drives the flow of electric current in a circuit. It is measured in volts and can be thought of as the force that pushes electrons through a circuit.

## 2. How is EMF different from voltage?

While EMF is the total energy driving the flow of electric current, voltage refers to the potential difference between two points in a circuit. In other words, EMF is the force behind the movement of electrons, while voltage is the measure of how much work those electrons can do.

## 3. What factors affect the EMF in a circuit?

The EMF in a circuit can be affected by several factors, including the type of power source (such as a battery or generator), the number of cells or sources in the circuit, and the resistance of the circuit components. Temperature and material properties can also impact the EMF.

## 4. Can EMF be measured?

Yes, EMF can be measured using a voltmeter. By connecting the voltmeter to different points in a circuit, the EMF can be calculated by measuring the potential difference between those points. However, it is important to note that EMF cannot be directly measured, as it is a theoretical concept.

## 5. What is the unit of measurement for EMF?

The unit of measurement for EMF is volts (V). This is the same unit used to measure voltage, as they are closely related concepts. However, it is important to distinguish between EMF and voltage, as they have different definitions and applications in a circuit.

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