Douglas Krantz - Technical Writer - Describing How It Works
Get the book Make It Work - Conventional Fire Alarms

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


Electron

Picture of an atom, with the electrons in layers around the nucleus.
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.

Electromotive Force

The Letter E
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.

 Voltage

EMF
Is Voltage



Measured in Voltage, EMF pushes and pulls on the electrons.

Electrical Current

The Letter I
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.

 Amperage (Amps)

Current
Is Electron
 Movement



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

The Letter R
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.

Resistance (Ohms)

Resistance
Counters
 Electron Flow



Measured in Ohms, resistance opposes electron flow. The greater the resistance, the less the electrons flow.

Resistance

Lots of water out of a pipe.
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.
Only a little water out of a pipe
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

Water flowing out of a pipe
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

A direct relationship between EMF 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

As the resistance goes up,the current goes down, and vice-versa.
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.

 Interrelated

The circle of Ohms Law
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
Ohm's Law
E(Voltage)   =   I(Amps)   x     R(Ohms)
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.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

Share This With Friends:

Post this by your fire alarm panel -- It shows the in-house fire alarm system and how it calls the fire department.

Go to the Fire Alarm Description Map Page of Douglas Krantzs Technicians Corner
Go to the Residential Life Safety Map Page of Douglas Krantzs Technicians Corner
Go to the Residential Life Safety Map Page of Douglas Krantzs Technicians Corner
Go to the Fire Alarm Description Map Page of Douglas Krantzs Technicians Corner
Go to the General Electrical Map Page of Douglas Krantzs Technicians Corner
Go to the Fire Alarm Maintaining Map Page of Douglas Krantzs Technicians Corner
Go to the Fire Suppression Map Page of Douglas Krantzs Technicians Corner
Go to the Guest Writer's Guidelines of Douglas Krantzs Technicians Corner
See Trivia on Douglas Krantzs Technicians Corner
This website uses cookies. See Privacy for details.
Get the book Make It Work - Conventional Fire AlarmsGet the book Make It Work - Conventional Fire AlarmsGet the book Make It Work - Conventional Fire AlarmsGet the book Make It Work - Conventional Fire AlarmsGet the book Make It Work - Conventional Fire Alarms
Get the book Make It Work - Hunting Ground Faults
Get the book Make It Work - Hunting Ground FaultsGet the book Make It Work - Hunting Ground FaultsGet the book Make It Work - Hunting Ground FaultsGet the book Make It Work - Hunting Ground FaultsGet the book Make It Work - Hunting Ground Faults
Reader's Favorite Articles

What is a Stair Pressurization Fan (SPF)?

Which Way Does Electricity Flow?

What's the Difference Between Class A and Class B?

What Makes the End of Line Resistor So Important?

What is a Flyback Diode?

What is a Fire Alarm System?

What is an RTU (Roof Top Unit)?

What Causes an Open NAC?

Recent Articles

Should the Generator Stop when the Horns Stop?

Why Can't I Reset the Panel After Disconnecting the SLC?

I'm Getting Desperate Dealing with False Alarms...

Help! I Have Some Weird NAC Troubles

Can the Fire Alarm System be Fixed so It Can Be Heard?

How Can a Door Holder be Hot and Buzzing?

Why Won't the Added Horns and Strobes Work?

What is the Difference Between a Fire / Smoke Damper and a Fire Damper

How do Pathways Affect Ground Faults?

Why Won't the Panel Show the Detectors?

When Testing, Why Isn't the LED Lit Continuously?

Why Don't All of the Smoke Detectors Act the Same?

Is There a Procedure to Install EST Detectors?

Does it harm the panel if the trouble occurs during a weekend and lasts 2 or 3 days?

The fire alarm bell to my house is going off...

How is an Addressable Elevator Capture Panel Connected to a Conventional Panel?

Why Does Closing Some Gatevalves Show Trouble?

Home Wateflow Switch - Do you know how to reset it?

How is a Pathway Classified?

Just Who Is the Authority Having Jurisdiction (AHJ)?

What are Pull-Up or Pull-Down Resistors?

Do we need horns and strobes in a building shell?

Don't Breathe Smoke

The Pump was Very Hot - What Happened?

Learn about fire alarms, one article at a time -

Keep up on the latest article!




No Charge - Unsubscribe Anytime