Calculate Internal Resistance: I, R, V & More

In summary, internal resistance is a concept used to explain why the terminal voltage of a real battery decreases as the current drawn from it increases. It can be represented by a resistor in series with the battery. To calculate the internal resistance, draw a circuit with the given values and solve for the unknown resistance.
  • #1
nslinker
22
0
How can I go about calculating internal resistance? I have variables I, R, and V but no idea on how to find the 'internal' resistance. Is this some sort of special case?
 
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  • #2
Your question needs to be a bit more specific.

Internal resistance is a concept used to account for the fact that the terminal voltage of a a real battery (as opposed to an ideal voltage source, whose voltage is constant, regardless of the current drawn from the source) drops as the current drawn from the battery increases. A simple electrical model of a battery is an ideal voltage source in series with a resistor representing the internal reistance. As current increases,, more voltage is dropped across the internal R and the battery terminal voltage decreases.
 
  • #3
Well, the question says "A 20 V battery delivers 107 mA of current when connected to a 74 ohm resistor. Determine the internal resistance of the battery."
 
  • #4
Just draw a circuit consisting of the 74 ohm resistor, the unknown resistance r in series and the 20V batteries. Then solve for r given the info in the question.
 

1. What is internal resistance?

Internal resistance is the resistance within a battery or any other power source that opposes the flow of electric current. It is caused by the materials used in the construction of the power source and the chemical reactions that occur within it.

2. How do you calculate internal resistance?

Internal resistance can be calculated using Ohm's law, which states that the internal resistance (R) is equal to the voltage (V) divided by the current (I). This can be represented by the equation R = V/I. The internal resistance can also be calculated by measuring the voltage across the terminals of the power source with and without a load, and using the voltage difference and the current through the load in the equation R = ΔV/I.

3. Why is internal resistance important?

Internal resistance is important because it affects the performance and efficiency of a power source. A high internal resistance can cause a decrease in the voltage output and a decrease in the overall power output. It can also cause the power source to heat up and potentially damage it.

4. How does internal resistance affect battery life?

The internal resistance of a battery can affect its overall lifespan. A high internal resistance can cause the battery to heat up and degrade faster. It can also cause a decrease in the available voltage and power, leading to a shorter lifespan. Therefore, it is important to consider the internal resistance when choosing a battery for a specific application.

5. What factors can affect the internal resistance of a power source?

The internal resistance of a power source can be affected by several factors, including the type of material used in the construction of the power source, the temperature, and the age of the power source. Additionally, the internal resistance can also be affected by the current flow and the load connected to the power source.

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