Enter the electromotive force, current, and load resistance into the calculator to determine the internal resistance.
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 effective resistance inside a source of electromotive force (such as a battery, generator, or power supply) that causes the terminal voltage to drop when current flows.
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 0.4 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: 10/0.4 - 20 = 5 ohms.
