# What is Ohm's law?

Ohm's Law states: "*The current flowing through a conductor
is directly proportional to the applied voltage, provided the
temperature of the conductor remains constant*."

It specifically refers to conductors and not resistors. And it takes into consideration the need to maintain a given temperature as the voltage and current vary. At the time, Georg Ohm already knew that allowing the temperature to vary would break the constant ratio.

Keep in mind that this was a historic new understanding that he had discovered was applicable to various conductors (metals).

Ohm's Law is by no means a universal law, and very few materials or electrical components actually 'obey' Ohm's Law. Those that do (some metals) are termed 'linear' or 'ohmic'; those that don't (most) are termed 'non-linear' or 'non-ohmic'.

Simply put, if the graph of voltage against current, plotted for variations in voltage, is a straight line, then Ohm's Law applies; if the graph is not a straight line, then Ohm's Law does not apply. And very few materials/devices produce a straight line graph. Based on this, you could say that 'Ohm's Law' is not a 'law' at all, but simply describes the behaviour of a limited range of materials.

So Ohm's Law doesn't apply to heated metals such as tungsten filaments, or to circuit components, such as diodes and to practically all other electronic devices.

The basic unit of electrical resistance was given the name 'The Ohm' in honor of Georg Ohm. The symbol for the unit is Ω, pronounced Omega. The ratio of a given voltage to resulting current will always tell us what the resistance happens to be for that particular instance. This is because the ratio of voltage to current is, by definition, resistance - however, this has nothing whatsoever to do with Ohm's Law, but is simply a definition of resistance!

E = I R

Voltage = Current times Resistance

As the alternate answers below clearly indicate, there is a widespread misunderstanding regarding Ohm's Law. Answer Resistance defines the relationships between (E) electromotive force in Volts and (I) current in Amperes. One ohm is defined as the resistance value through which one volt will maintain a current of one ampere. In other words, an ohm is a volt per ampere.

(I) Current is what flows on a wire or conductor like water flowing down a river. Current flows between points of different voltage. Current is measured in (A) Amperes, abbreviated: amps.

(E) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in Volts.

(R) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in Ohms.

Answer The statement taught in electrical training is "Current is directly proportional to the applied EMF and inversely proportional to the resistance of the circuit".

Ohm's law: When there is a potential (Voltage-V) different between two ends of a conductor a follow of charges will be created (The current-I) through this conductor which is directly proportional to the voltage difference and inversely proportional to the resistance of the conductor (Resistance-R ).

I α Vdifference

I α 1/R

I=Vdifference/R : Current increases with increase of voltage, but decreases with the increase of the resistance

Answer Ohms Law states that the amount of current that passes through an object is directly proportional to the potential voltage across that object, and inversely proportional to the resistance, or electrical impedance, of that object. In other words: * as voltage goes up, the current goes up by the same proportional amount * as the impedance goes up, the current is reduced by the same proportional amount. Ohms Law can be stated mathematically as:

I = E/R Where: I is the current, E is the voltage, R is the resistance

As you can see from the above formula, if the voltage were to double, then so would the current. If the resistance were to triple, then the current would be one-third of its former value. You can use Ohms Law to calculate any value if you know the other two. These are expressed mathematically as: V = I x R (to calculate Voltage) R = V / I (to calculate Resistance) In the above calculations, V is measured in 'volts', I is measured in 'amperes' (or amps), and R is measured in Ohms.

Ohm's Law states Voltage = Current x Resistance. Except in unusual circumstances the resistance "R" is a constant. When you increase voltage, current increases.

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**Ohm's Law** states that 'the current flowing through a
conductor at constant temperature is directly proportional to the
potential difference across that conductor'.

Ohm's Law is by no means a universal law, and *only*
applies to those conductors or devices where the ratio of voltage
to current is constant over a wide range of potential differences.
These materials are termed 'ohmic' or 'linear', whereas those
materials and devices that do *not* obey Ohm's Law (and there
are a great many!) are termed 'non-ohmic' or 'non-linear'. Examples
of non-ohmic materials and devices include tungsten (lamp
filaments), diodes, electrolytes, etc.

The ratio of *voltage to current* is termed
**resistance** *(R = E/I)*, and is derived from the
definition of the **ohm**, and *not* (as many people think)
from Ohm's Law. This equation can be applied to *both* ohmic
*and* non-ohmic materials and devices, so applies whether or
not Ohm's Law is followed.