# What is a Magnetic Field

## Introduction

Mathematical descriptions of the magnetic influence of electric currents and magnetic materials are called magnetic fields. At any given point, the field is specified by a magnitude (strength) and a direction. This makes it a vector field. In general, a magnetic field is defined in terms of the Lorentz Force it exerts on moving electric charges.

Moving electric charges and the inherent magnetic moments of elementary particles associated with fundamental quantum property, their spin, produce magnetic fields. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field tensor; the aspect of the electromagnetic field that is seen as a magnetic field is dependent on the reference frame of the observer. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons.

Both ancient and modern society have employed magnetic fields for specific uses and influences. Even the Earth itself produces its own magnetic field, which helps us navigate in planes, and other navigational instruments. Electric motors and generators that supply power employ magnetic fields. Magnetic circuits, such as those seen in transformers, has its own field of study — magnetic circuitry.

A magnetic field can be defined in many ways based on the effects it has on its personal environment. If, for instance, a particle has an electric charge of “q”, and moves in a magnetic field with a velocity, “v”, it experiences force, “f”, called the Lorentz Force.

## Lorentz Force Law:

Devices used to measure the local magnetic field are called magnetometers. These instruments of measure include using a rotating coil, Hall effect magnetometers, NMR magnetometers, SQUID magnetometers, and fluxgate magnetometers. Magnetic fields in/of distant astronomical objects are measured through their effect on locally charged particles. For example, a field line with electrons spiraling around it produces synchrotron radiation, which we detect in radio waves.

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