Ohm's law and power calculator
Online calculator for calculating voltage, current, resistance and power
This fuction calculate the voltage U , the current I , the resistance R or the power P . Two of the values must be known.
Enter two of the four values, then click the 'Calculate' button.
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Ohm's law and power
Ohm's law is a fundamental principle of electrical engineering and electronics. It states the relationship between voltage, current and electrical resistance. The law states that voltage is equal to current multiplied by resistance. It reads:
\[U=I·R\]
- \( U \) is the voltage in volts (V)
- \( I \) is the current in amperes (A)
- \( R \) R is the resistance in ohms (Ω)
- \( P \) is the power in watts (W)
The electrical power is not, strictly speaking, part of Ohm's law. The formula has been included here, however, because they are closely related. The electrical power P is measured in watts (W) and can be calculated in different ways, depending on which quantities are given. There is a general formula for power: \[P=U·I\]
Variations of Ohm's Law
To calculate voltage when resistance and current or power are known
\(\displaystyle U=R · I\) \(\displaystyle \ \ \ \ \ =\sqrt{P · R}\) \(\displaystyle \ \ \ \ \ =\frac{P}{I}\)
To calculate current when voltage and resistance or power are known
\(\displaystyle I=\frac{U}{R}\) \(\displaystyle \ \ \ \ \ =\frac{P}{U}\) \(\displaystyle \ \ \ \ \ =\sqrt{\frac{P}{R}}\)
To calculate resistance when voltage and current or power are known
\(\displaystyle R=\frac{U}{I}\) \(\displaystyle \ \ \ \ \ =\frac{P}{I^2}\) \(\displaystyle \ \ \ \ \ =\frac{U^2}{P}\)
To calculate power when voltage and current or resistance are known
\(\displaystyle P=U · I\) \(\displaystyle \ \ \ \ \ =I^2·R\) \(\displaystyle \ \ \ \ \ =\frac{U^2}{R}\)
Examples 1
Calculating the voltage when the current and resistance are known:
Suppose a current of \(I=2 \ A\) flows in a circuit and the resistance is \(R=5 \ Ω\)
\[U=I·R=2 \ A · 5 \ Ω=10 \ A\]The voltage is therefore \(10 \ V\).
Examples 2
Calculating power with resistance and current
If the resistance is \(R=4 Ω\) and the current is \(I=3A\), then the power is:
\[P=I^2·R= (3 \ A)^2 · 4 \ R=9· 4=36 \ W\]
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