Circuit for determining the internal resistance of a dry cell

In summary, to determine the internal resistance of a dry cell, you would need to set up a circuit with a voltmeter and ammeter in series, with a variable resistor (rheostat) as the load. You can measure the EMF by measuring the open circuit voltage and then measure the voltage drop across the load to calculate the internal resistance. The amount of voltage drop needed may vary depending on the type of battery being tested.
  • #1
jackmannn
3
0
What sort of circuit would I have to set up to figure out the internal resistance of a dry cell? Also, what would i need to be measuring and doing etc, to find this internal resistance?

Thanks, Jack.
 
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  • #2
A battery is considered to be an EMF in series with a resistor.

You can measure the EMF by measuring the open circuit voltage of the battery. There is no voltage drop across a resistor if there is no current flowing through it.

To put a load on the battery and measure the current and voltage, you could use something like the attached diagram.

A voltmeter monitors the output voltage. A variable resistor R is placed in series with the ammeter.
You can monitor the voltage while the heavy load (R) is placed across the battery. A large rheostat would be suitable for R.

Suppose R makes the output voltage drop to half. Then you could say that R is equal to the internal resistance.
You can calculate the value of R by measuring the voltage across it and the current through it.
The voltage does not have to drop to half. If you were testing a rechargeable cell, a NiMH or NiCd cell, you would not do this because these can deliver very large currents. So, maybe a 10% drop would be OK for these.

You just calculate the value of the internal resistance knowing the current flowing and the voltage drop between no load and the measured load.
 

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  • #3


To determine the internal resistance of a dry cell, you would need to set up a circuit that includes the dry cell, a variable resistor, and a voltmeter. The variable resistor allows you to control the amount of current flowing through the circuit, and the voltmeter measures the voltage across the dry cell.

First, set up the circuit by connecting the positive terminal of the dry cell to one end of the variable resistor, and the negative terminal to one end of the voltmeter. Then, connect the other end of the voltmeter to the other end of the variable resistor. This creates a series circuit.

Next, adjust the variable resistor to a high resistance and record the voltage reading on the voltmeter. Then, gradually decrease the resistance of the variable resistor and record the voltage readings at different resistance values. Make sure to keep the current constant by adjusting the variable resistor.

Using Ohm's Law (V=IR), you can calculate the internal resistance of the dry cell by dividing the change in voltage by the change in current (ΔV/ΔI). This will give you the internal resistance in ohms.

It is important to note that the internal resistance of a dry cell can vary depending on its state of charge and age, so it is recommended to take multiple readings and calculate an average for a more accurate result.

In summary, to determine the internal resistance of a dry cell, you would need to set up a series circuit with a variable resistor and voltmeter, and measure the voltage at different resistance values to calculate the internal resistance using Ohm's Law.
 

1. How does a circuit determine the internal resistance of a dry cell?

A circuit for determining the internal resistance of a dry cell typically consists of a known resistor, a voltmeter, and the dry cell being tested. The known resistor is connected in series with the dry cell, and the voltmeter is connected in parallel to the dry cell. By measuring the voltage drop across the known resistor and the dry cell, the internal resistance of the dry cell can be calculated using Ohm's law (R = V/I).

2. What is the purpose of determining the internal resistance of a dry cell?

Determining the internal resistance of a dry cell can provide valuable information about the cell's health and performance. It can also help in selecting the appropriate dry cell for a specific application.

3. Can the internal resistance of a dry cell change over time?

Yes, the internal resistance of a dry cell can change over time as the cell is used and its chemical reactions slow down. This can result in a decrease in the cell's voltage and overall performance.

4. Are there any safety precautions to keep in mind when using a circuit to determine the internal resistance of a dry cell?

Yes, it is important to use caution when working with electricity. Make sure the circuit is disconnected from any power source before making any changes. Also, be careful when handling the dry cell as it can become hot during the testing process.

5. Are there any other methods for determining the internal resistance of a dry cell?

Yes, there are other methods, such as using a Wheatstone bridge or a potentiometer. However, the circuit method is the most common and simplest way to determine the internal resistance of a dry cell.

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