# Electromagnetism

Electromagentism is the heart of Electrical Engineering. It is what we study and what we utilize to create devices that do all sorts of useful things like motors that perform work or logic circuits that do computation. Electromagentism is actually a single phenomenon, not just the collection of electricity and magnetism.

We know this thanks to James Clerk Maxwell (1831-1879) who is one of the greatest physicists of all time and sports a very impressive beard. He authored the famous Maxwell’s Equations, which is a set of 4 partial differential equations that describe the behaviors and relationships of electromagnestism. These equations are beyond the scope of this website, but are certainly among the most interesting and profound equations in physics.

https://en.wikipedia.org/wiki/James_Clerk_Maxwell

#### Electromagnetic Force

– Units: Newtons (N); Symbol: F

Electromagnetic force is one of the 4 fundamental forces of nature. This force arises from the interaction of electromagnetic fields and electrically charged particles.

#### Electric Charge

– Units: Coulombs; Symbol: Q, q, e

Electric Charge is a property of matter that causes the matter to experience a force when in the presence of an electromagnetic field. An electric charge can be positive or negative with Protons and Electrons being common carriers of postive and negative charge, repectively. Something that has more protons than electrons has a net positive charge (e.g. ionic sodium in table salt). Something that has more electrons than protons has a net negative electrical charge (e.g. ionic chlorine in table salt).

#### Magnetic Charge

There is no such thing as magnetic charge. Positive and negative magnetic poles cannot exist apart from each other like positive and negative electric charges can. Magnetic fields are produced by electric charges in motion. Stationary electric charges do not produce a magnetic field, but do produce an electric field.

#### Electric Field

– Units: Newtons/Coulombs (N/C) or Volts/meter (V/m); Symbol: E

An electric field is a region in which electric force is exerted. It is produced by electric charges, and also induced by magnetic fields that vary in time.

#### Magnetic Field

– Units: Teslas (T) or Newtons/(meter*Ampere) (N/(m*A)); Symbol: B

A magnetic field is a region in which magnetic forces are exerted, and they are produced by moving electric charges (i.e. current). Magnetic and electric fields are always oriented at 90 degrees relative to each other.

#### Voltage

– Units: Volts (V) or Joule/Coulomb (J/C); Symbol: V, v

Voltage is electric potential difference. It is the difference in electric potential energy between two points, per unit electric charge. Voltage is by nature a relative value, always defined between two points and not at a single place. The positive voltage point has higher potential energy, and the negative voltage point has lower potential energy.

#### Current

– Units: Amperes (A) or Coulomb/second (C/s); Symbol: I, i

Current is the flow rate of electric charge. Positive current is the flow of positive charges from higher voltage to lower voltage. EEs consider current to be the flow of positive charge, because the discipline was established before electrons were discovered. Electrons are negatively charged and are the actual moving charge carrier producing current in electronics. But the math works out fine, since mathematically, the flow of positive charges in one direction is the same as the flow of negative charges in the opposite direction.

#### Power

– Units: Watts (W) or Joules/second (J/s); Symbol: P, p

Power is the rate at which energy is generated or consumed. Electric Power is equal to Voltage times Current: P = V * I.

#### Energy

– Units: Joules (J); Symbol: E

Energy is equal to Power times Time: E = P * T. If Power varies over time, Energy is the time integral of Power.

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