Internal Resistance Calculator
⚡ Electricity & magnetism. Use the Internal resistance (EMF) formula to find emf ε, current, external resistance, internal resistance: pick the value you want, type the others, and the answer updates as you go.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| EMF ε | V |
| Current | A |
| External resistance | Ω |
| Internal resistance | Ω |
Worked example
Find the emf ε when Current = 2 A, External resistance = 5.5 Ω, Internal resistance = 0.5 Ω.
Using ε = I(R + r): EMF ε = 12 V.
Frequently asked questions
What is the formula for Internal resistance (EMF)?
ε = I(R + r).
What do the letters stand for, and what units are used?
EMF ε in V, Current in A, External resistance in Ω, Internal resistance in Ω.
How do you calculate emf ε?
Put the values into ε = I(R + r). For example, with Current = 2 A, External resistance = 5.5 Ω, Internal resistance = 0.5 Ω, emf ε = 12 V.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (emf ε, current, external resistance, internal resistance) and fill in the others: it rearranges the formula for you.
