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• Ohm's law - calculator and formulas •
Resistance, current, and voltage
V = R × I I = V / R R = V / I
The formulas of Ohm's Law
Ohm's Law can be rewritten in three ways for calculating current, resistance, and voltage.
If a current I should flow through a resistor R, the voltage V can be calculated.
V = R × I
If there is a voltage V across a resistor R, a current I flows through it. I can be calculated.
I = V / R
If a current I flows through a resistor, and there is a voltage V across the resistor R can be calculated.
R = V / I
| Quantity | Symbol | Unit | Sign |
| Voltage | V or E | volt | V |
| Current | I | ampere (amp) | A |
| Resistance | R | ohm | Ω |
| Power | P | watt | W |
Tip: Ohm's magic triangle
The magic V I R-triangle can be used to calculate all formulations of Ohm's Law.
Use a finger to hide the value to be calculated. The other two values then show
how to do the calculation.
The symbol I comes from "International Ampere" and R from "Resistance",
and Volts = V or E, the potential difference, also called voltage drop.
If you need the unit of power P = V × I
look for the 
Big Power Formulas:
Calculations: power, voltage, current, resistance, and power
Cross-sectional area - cross section - slice plane
Now there is the question:
How can you calculate the cross sectional area (slice plane) A
from the wire diameter d and vice versa?
Calculation of the cross section A (slice plane) from diameter d:
r = radius of the wire
d = diameter of the wire
Calculation diameter d from cross section A (slice plane):
Cross section A of the wire in mm2 inserted in this formula gives the diameter d in mm.
Calculation: Round cables and wires:
• Diameter to cross section and vice versa •
Electrical voltage V = R × I
Electrical voltage = resistance × amperage
Please enter two values, the third value will be calculated.
Electric power P = V × I
Electric power = voltage × amperage
Please enter two values, the third value will be calculated.
| Ohm's law. V = I × R, where V is the potential across a circuit element, I is the current through it, and R is its resistance. This is not a generally applicable definition of resistance. It is only applicable to ohmic resistors, those whose resistance R is constant over the range of interest and V obeys a strictly linear relation to I. Materials are said to be ohmic when V depends linearly on R. Metals are ohmic so long as one holds their temperature constant. But changing the temperature of a metal changes R slightly. When the current changes rapidly, as when turning on a lamp, or when using AC sources, slightly non-linear and non-ohmic behavior can be observed. For non-ohmic resistors, R is current-dependent and the definition R = dV/dI is far more useful. This is sometimes called the dynamic resistance. Solid state devices such as thermistors are non-ohmic and non-linear. A thermistor's resistance decreases as it warms up, so its dynamic resistance is negative. Tunnel diodes and some electrochemical processes have a complicated I to V curve with a negative resistance region of operation. The dependence of resistance on current is partly due to the change in the device's temperature with increasing current, but other subtle processes also contribute to change in resistance in solid state devices. |
Color Code Calculator for Resistors
In acoustics we use ohm's law as acoustic equivalent
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