# How to Determine the EMF of a Battery Using Two Voltmeters?

• palkia
In summary, to measure the emf of a battery, you will need to use two voltmeters and solve for the unknowns using simultaneous equations. The equations will involve the EMF, the voltmeter readings, and the resistance of the voltmeters and the battery.
palkia

## Homework Statement

We have to measure emf of a battery. We have to voltmeters. Each of them when connected alone across the battery, they read V1 = 0.9V and V2 = 0.6V and when both of them are connected to the battery simultaneously, they both read V3 = 0.45V . What is the emf of battery

E-ir=V

## The Attempt at a Solution

I don't know how to proceed...I thought the voltage across the battery will be it's emf when connceted without a load but it is showing different readings for the voltmeter

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Find out the difference between an "ideal" voltmeter and a "real" voltmeter. Likewise ideal and real batteries.

palkia
ideal voltmeter-Which doesn't influence the circuit

Real voltmeter-Which has resistance that is not infinitely largeSame for battery

okay so it makes sense that it shows different readings now...but still How can I proceed if they have different resistance

Ok so you will need to decide how many unknowns there are and give them names (eg R1 is the resistance of Voltmeter 1).

Then write some simultaneous equations and if you have enough then you can solve them.

palkia
V1=E- I1R1
V2=E-I2R2
V3=E-I3R3

It's getting bigger to solve as I tried

In the last case,when we connect the voltmeters ,my book states that I3=I1+I2 but I am not sure How it came

palkia said:
V1=E- I1R1
V2=E-I2R2
V3=E-I3R3

I don't think those are correct. What about the battery resistance? With just one voltmeter connected the circuit looks like this...

So the equations would be

V1 = EMF - (I1*RB)
you also know
I1 = V1/R1

V2 = EMF - (I2*RB)
you also know
I2 = V2/R2

With both meters connected...

V3 = EMF - (I3*RB)
you also know
I3 = V3/R3
and
R3 = R1 in parallel with R2

#### Attachments

• Battery Circuit.jpg
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palkia

## 1. What is EMF of a battery?

The EMF (electromotive force) of a battery is the amount of potential energy that the battery can provide to an electric circuit. It is measured in volts (V) and is essentially the voltage difference between the positive and negative terminals of the battery.

## 2. How is EMF different from voltage?

EMF and voltage are often used interchangeably, but technically they are slightly different. EMF is the amount of potential energy that a battery can provide, while voltage is the measure of the potential difference between two points in an electric circuit. EMF takes into account the internal resistance of the battery, while voltage does not.

## 3. What factors affect the EMF of a battery?

The EMF of a battery can be affected by several factors, including the type of battery (e.g. alkaline, lithium-ion), the materials used in the battery's electrodes, the temperature, and the age of the battery. Additionally, the EMF may decrease over time as the battery discharges.

## 4. How is EMF measured using a voltmeter?

To measure the EMF of a battery using a voltmeter, the voltmeter is connected to the positive and negative terminals of the battery. The voltmeter will then display the voltage reading, which is the EMF of the battery. It is important to note that the voltmeter itself will introduce a small amount of resistance and may slightly affect the EMF reading.

## 5. Can a voltmeter measure the EMF of any type of battery?

No, a voltmeter can only measure the EMF of batteries that are still producing a voltage. If a battery is completely dead, the voltmeter will not be able to measure its EMF. Additionally, different types of batteries may require different types of voltmeters for accurate readings. It is always best to consult the manufacturer's instructions for the proper use of a voltmeter with a specific type of battery.

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