What Does E=IR Really Mean?
If it isn't just a word, and it isn't really something to be memorized in order to pass a test, what do the letters in Ohm's Law really mean?
By Douglas Krantz
The electrons are found in layered clouds around the nucleus of atoms. The protons in the atom don't move from atom to atom, but the electrons can be pushed and pulled from atom to atom using electrical force. The force is called Electromotive Force (EMF). EMF is measured in voltage.
The letters in Ohm's Law show a relationship between voltage, current, and resistance, and at the heart of that relationship is the electron.
Electomotive Force (EMF), like pressure pushing on water, or like gravity pulling everything on earth, is what pushes and pulls electrons to cause them to jump from one atom to the next. Electromotive Force is measured in Voltage.
"E" stands for Electromotive Force (EMF). It's the driving muscle that moves the electrons.
Measured in Voltage, EMF pushes and pulls on the electrons.
Electrical Current is the number (quantity) of electrons going past a given point in an electrical circuit, like the number of cubic meters of water that goes over a falls in a second. Electrical Current is measured in Amperage, or Amps for short.
"I" stands for "Intensité de Courant" (French), or Current Intensity. André-Marie Ampere, who discovered electrical current, used this symbol.
Measured in Amps, and hopping from one atom to the next, the organized movement of electrons going past a point is electrical current, or "I".
Resistance is the amount of opposition to electrical current. This can be likened to the diameter of a pipe resisting the flow of drainage from the bathtub. The larger the pipe (lower resistance) the faster gravity can pull the water out of the bathtub.
"R" stands for Resistance. It restricts, or slows down, the movement of electrons.
Measured in Ohms, resistance opposes electron flow. The greater the resistance, the less the electrons flow.
A greater amount of water will flow when the valve is opened wider; more electrons will flow when there is less resistance.
Assuming the electromotive force remains the same, reducing the resistance, like opening a valve on a water pipe, will increase the number of electrons that flow.
A lessor amount of water will flow when the valve is more closed; less electrons will flow when the resistance is greater.
The opposite is also true, increasing the resistance will reduce the number of electrons that flow.
Current Flow - Quantity of Electrons
Greater water pressure pushes more water through the same pipe; greater electromotive force will push more electrons past the resistance. Lessor water pressure means less water; lessor electromotive force means fewer electrons.
The quantity of electrons flowing, electrical current, is determined by the electromotive force - reduced by the resistance.
Similarly, the quantity of water flowing is determined by water pressure, reduced by the restriction of the pipe.
EMF (voltage) Does not affect R(Resistance)
R(Resistance) Does not affect EMF(voltage)
Electromotive Force (EMF) and Resistance (R) do not affect, or change, each other.
Voltage and Current
The greater the EMF (voltage) the greater the current (amperage); the lessor the EMF the lessor the current.
The amount of electromotive force (voltage) directly affects current flow. Current goes up and down as EMF goes up and down.
Resistance and Current
The greater the resistance (Ohms), the lessor the current (Amps); the lessor the resistance, the greater the current.
The amount of resistance inversely affects current flow. As resistance goes up, current goes down, and as resistance goes down, current goes up.
Voltage and Resistance don't actually affect each other, Voltage (E) and Resistance (R) both will change the current (I).
The relationships between the electromotive force, current and resistance are all interrelated, and described in a single formula, or law.
The Formula is
Having serviced fire alarm systems for nearly 20, Douglas Krantz has compiled his knowledge of the causes of Ground Faults and how to reliably detect them into the book Make It Work - Hunting Ground Faults
. The book shows the three types of ground fault, what equipment should be used with each type of ground fault, and how to locate those hard-to-find ground faults.
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