Enter the electromotive force, current, and load resistance into the calculator to determine the internal resistance.

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## Internal Resistance Formula

The following formula is used to calculate an internal resistance.

r = (e / i) - R

- Where r is the internal resistance (ohms)
- e is the electromotive force (Volts)
- i is the current (amps)
- R is the resistance of the load in the circuit.

To calculate internal resistance, divide the electromotive force by the current, then subtract the resistance of the load.

## Internal Resistance Definition

Internal resistance is the total resistance to electron flow that arises from the internal structures of a circuit.

## Internal Resistance Example

How to calculate the internal resistance?

**First, determine the electromotive force.**For this example we will say this value is 10 V.

**Next, determine the current.**For this example we will assume a current of 10 amps.

**Next, determine the load resistance.**For this example the value is 20 ohms.

**Finally, calculate the internal resistance.**Using the formula we find the internal resistance to be: 10/10 – 20 = -19 ohms.