Ohm's law calculation calculator calculate power formulas mathematical ohm's law pie chart electric voltage drop electric current resistance formula watt's law emf magic triangle equation tip online voltage volts resitor resistance amps amperes audio engi (2024)

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Formulas:V = I × RI = V / RR = V / I

The mathematical 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.
First Version of the (voltage) formula: V = I × R

If there is a voltage V across a resistor R, a current I flows through it. I can be calculated.
Second Version of the (current) formula: I = V / R

If a current I flows through a resistor, and there is a voltage V across the resistor. R can be calculated.
Third Version of the (resistance) formula: R = V / I

All of these variations of the so called "Ohm's Law" are mathematically equal to one another.

What is the formula for electrical current?
When the current is constant:
I = Δ Q / Δ t
I is the current in amps (A)
Δ Q is the electric charge in coulombs (C),
that flows at time duration of Δ t in seconds (s).

Voltage V = current I × resistance R

Power P = voltage V × current I

In electrical conductors, in which the current and voltage are proportional
to each other, ohm's law apply: V ~ I or V ⁄ I = const.

Constantan wires or other metal wires held at a constant temperature meet well ohm's law.

"V ⁄ I = R = const." ist not the law of ohm. It is the definition of the resistance.
Thereafter, in every point, even with a bent curve, the resistance value can be calculated.

For many electrical components such as diodes ohm's law does not apply.

"Ohm's Law" has not been invented by Mr. Ohm

Tip: Ohm's magic triangleThe magic V I Rtriangle 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.

Voltage drop calculations - DC / single phase calculation
The voltage drop V in volts (V) is equal to the wire current I in amps (A) times twice
the wire length L in feet (ft) times the wire resistance per 1000 feet R in ohms (Ω / kft)
divided by 1000:
V_drop (V) = I_wire (A) × R_wire (Ω)
= I_wire (A) × (2 × L (ft) × R_wire (Ω / kft) / 1000 (ft / kft))The voltage drop V in volts (V) is equal to the wire current I in amps (A) times twice
the wire length L in meters (m) times the wire resistance per 1000 meters R in ohms
(Ω / km) divided by 1000:
V_drop (V) = I_wire (A) × R_wire (Ω)
= I_wire (A) × (2 × L (m) × R_wire (Ω / km) / 1000 (m / km))

If the unit of power P = I × V and of voltage V = I · R is needed,
look for "The Big Power Formulas":
Calculations: power (watt), voltage, current, resistance

Some persons think that Georg Simon Ohm calculated the "specific resistance".
Therefore they think that only the following can be the true ohm's law.

Quantity of resistance
R = resistance	Ω
ρ = specific resistance	Ω×m
l = double length of the cable	m
A = cross section	mm2

Electrical conductivity (conductance) σ (sigma) = 1/ρ
Specific electrical resistance (resistivity) ρ (rho) = 1/σ

Difference between electrical resistivity and electrical conductivity

The conductance in siemens is the reciprocal of the resistance in ohms.

Simply enter the value to the left or the right side.
The calculator works in both directions of the ↔ sign.

For all conductors the specific resistivity changes with the temperature. In a limited
temperature range it is approximately linear:
where α is the temperature coefficient, T is the temperature and T₀ is any temperature,
such as T₀ = 293.15 K = 20°C at which the electrical resistivity ρ (T₀) is known.

Cross-sectional area - cross section - slice plane

Now there is the question:
How can we 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 •

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 light, 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.

How electricity works.
Ohm's Law clearly explained.

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