How one measures magnetic Feild?

Answer 1

In physics, a magnetic field is that part of the electromagnetic field that exists when there is a changing electric field. A changing electric field can be caused by the movement of an electrically charged object, as in an electric current; or a combination of the orbit of an electron around an atom and the spin of electrons themselves, as in a permanent magnet.

You can see all the details about it in the below mentioned site : http://en.wikipedia.org/wiki/Magnetic_field

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Answer 2

Use a Gauss meter? And milk comes from the grocery store.

The easiest kind of magnetic field to measure is one that either oscillates or rises quickly from zero. Insert a wire loop of area A and inductance L monitored by an oscilloscope terminated with resistance R. The voltage induced by a magnetic field equals the time derivative of the magneic flux threading a closed loop. So, the voltage recorded is equals A*dB/dt, provided the loop is small enought that B varies little over the area. Time integration (electronic or digital) gives you B. The time resolution (minimum time that B can change by a significant amount to get an accurate measurement) is L/R. For a static magnetic field, one may use the same principle by spinning the loop such that the flux oscillates from +A*B to -A*B. I don't believe a commercial Gauss meter works that way, though, (with moving parts). Maybe someone else can explain how.

Answer 3

Magnetic fields are measured by a device called Gauss meter

Magnetic field assessment involves two distinctly different measurement protocols used for two different purposes. The most common is the measurement of the maximum field strength, used to locate the source of a field, determine its direction and its strength. Typically, power line measurements or general background measurements are of this type. The other is concerned with exposure and is usually associated with the measurement of a particular appliance, like a computer monitor.

It is impossible to avoid exposure to low frequency magnetic fields in modern society - there is always some level of background radiation present. This background radiation could be coming from a number of sources and must be taken into consideration when you are attempting to measure fields from a particular appliance or source. Before any assessment of the emissions from a computer monitor or other appliance is possible, it is necessary to first determine the strength of the background field. In some cases, that field will be greater than that which is coming from the monitor, making measurements of the monitor's emissions impossible.

In order to determine background radiation levels, turn off the computer monitor to be measured and take a set of readings of the area around the unit. If the background radiation is high, (say, several milliGauss), the contribution of the monitor to the environment may not be measurable. (In recognition of this fact, the Swedish specification MPR II requires that the background levels be no greater than 0.4 milliGauss in order for testing to be valid.)

If two sources are close enough for their fields to interact, they could amplify each other or cancel each other, depending on distance and field direction. Thus, it is possible for the field strength measurement to increase after turning off a source.