# Measuring Internal Resistance of Zinc Carbon Cell: Tips & Tricks

• StaceyParker
In summary, the conversation discusses an experiment to measure the internal resistance of a zinc carbon cell and how to find the EMF of the battery. The formula ε= IR + Ir is mentioned, but the speaker is confused about how to use it. It is suggested to find the internal resistance through research or by looking at the battery itself. Additionally, the speaker is advised to test the voltage of the battery when not attached to the circuit and to plot various values of V against the current I to determine the EMF.
StaceyParker
I'm doing an experiment to measure the internal resistance of a zinc carbon cell (battery) and have slightly confused myself! Do I use the ε= IR + Ir formula? And if so how in the world do I use it! I know that I can work out R by using V and I values but how do I find the EMF of the battery? And what value do I use for I cos I have hundreds cos current isn't a constant!
I've royally confused myself!

The emf of the battery should be listed on the battery, the internal resistance can be found either through research or it may even be indicated on the battery

$$\Delta V=EMF-IR$$

The internal resistance can be experimentally determined by hooking the battery up to the resistor,

the total V of the circuit will be $$\Delta V_{circuit}=I(R)=I(R_{eq}+R_{internal})$$

The emf will be the terminal voltage when there is no current flowing. THat is, test the voltage of the battery when it is not attached to the circuit.

You could do a plot of various values of V (=IR) against the current I. As shown by the formula IR = EMF - Ir, you will see that the gradient will be -r, whilst the y intercept will be the EMF.

## 1. What is the purpose of measuring the internal resistance of a zinc carbon cell?

The purpose of measuring the internal resistance of a zinc carbon cell is to determine its overall health and performance. This measurement can provide important information about the cell's ability to maintain a steady voltage and deliver power to a circuit.

## 2. How is the internal resistance of a zinc carbon cell measured?

The internal resistance of a zinc carbon cell can be measured by connecting it to an external load and measuring the voltage drop across the cell at different levels of current. This data can then be used to calculate the internal resistance using Ohm's law.

## 3. What factors can affect the internal resistance of a zinc carbon cell?

The internal resistance of a zinc carbon cell can be affected by factors such as temperature, age, and load current. Higher temperatures can increase the internal resistance, while aging of the cell can also cause an increase in resistance. Additionally, high load currents can cause a temporary increase in internal resistance due to chemical reactions within the cell.

## 4. What are some tips for accurately measuring the internal resistance of a zinc carbon cell?

To get an accurate measurement of the internal resistance of a zinc carbon cell, it is important to use a reliable, calibrated multimeter and ensure that the cell is fully charged. It is also recommended to take multiple measurements at different load currents to get a more accurate average. Additionally, keeping the cell at a consistent temperature can help minimize any fluctuations in the measurement.

## 5. Can the internal resistance of a zinc carbon cell be reduced?

While the internal resistance of a zinc carbon cell cannot be reduced, it can be improved by using a higher quality cell or by connecting multiple cells in parallel. This will effectively lower the overall internal resistance and improve the cell's performance. However, it is important to note that this will also increase the cell's overall capacity, meaning it will have a shorter lifespan.

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