# What is Magnetic field strength: Definition and 102 Discussions

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors.
In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter (A/m). B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second2 per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum, the two fields are related through the vacuum permeability,

B

/

μ

0

=

H

{\displaystyle \mathbf {B} /\mu _{0}=\mathbf {H} }
; but in a magnetized material, the terms differ by the material's magnetization at each point.
Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature.
Magnetic fields are used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is conceptualized and investigated as magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.

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1. ### I Magnetic field strength of a stack of magnets

I know that for a single cylindrical neodymium magnet, the formula $$\displaystyle{\displaylines{B(z)=\frac{μ_0M}{2}(\frac{z}{\sqrt{z^{2}+R^{2}}}-\frac{z-L}{\sqrt{(z-L)^{2}-R^{2}}})}}$$ shows the relationship between the magnetic field strength and the distance between the magnet. I was...
2. ### I Calculating Magnetic field strength of a magnet

I have been trying to calculate the magnetic flux thought a single loop of wire occurring from a magnet (meaning it has a nonuniform field), so I have the following equation: Φ=∮BdAcosθ Now my problem is that I do not know how to calculate the magnetic field strength (B)of that magnet (which...
3. ### A What Superconductor Can Have The Highest Magnetic Field Strength?

Hello, I asked a question about superconductors in 2020 and I was now wondering what superconducting chemical/material can have the highest magnetic field strength before the superconductivity is destroyed by it? Secondly, What the is maximum magnetic field strength of said material in Tesla per...
4. ### How to find an expected value for magnetic field strength?

Our class modified an experiment to measure the magnetic field strength in mT between 5cm and 30cm, and I have plotted data and found that the relationship resembles a power relationship (using a log vs log graph). In order to find the percentage uncertainty for the whole experiment I need the...
5. ### How does the saturation flux density affect magnetic field strength?

So I'm confused what the Saturation Flux Density is referring to. Defintion says it is when you no longer get an increase in H-field when increasing external B-field. So, does the satuation flux mean the core can only create fields UP TO that saturation flux, or that it can make a stronger...
6. ### Engineering Magnetic field strength of an electromagnet (coil wound around a bobbin)

I am trying to design an electromagnet which consists of a copper PVC sheathed wire wound around a cylindrical plastic spool of Circumference (C) = pi x diameter. The spool has a hollow body of diameter D1. This wire has maximum length (L), cross sectional area A, resistivity P. The spool once...
7. ### Measuring Magnetic Field Strength of a Cylindrical Magnet

Hello, Today I am wondering if anyone can help me quantify the strength of the magnetic field created by a permanent cylindrical magnet. I have been able to find equations online for the strength of the field within the z axis, (ie. the longitudinal length) but I would like to know the strength...
8. ### Finding the Earth's magnetic field strength using a Galvanometer

Homework Statement [/B] I am working on a experiment on finding the Earth's magnetic field strength in Denmark. Using a Galvanometer and a constant power source of 5.1V and slowly adjusting the resistance, I was able to find the changes in angle in relation to the changes of current. 2...
9. ### Calculating Magnetic Field Strength in a Stator DC Motor

Hey, I need a little help I know in a DC motor there are permanent magnet and also coil So my question is, what is the equation to calculate the magnetic field strength in a stator dc motor compound?
10. ### Magnetic field strength at a distance

Hopefully, a simple question with a simple answer. I have a flat magnet (assume infinite long and wide) with a field strength at the surface of (for simplicity) exactly 1Tesla. What will the field strength be (in air) 1mm away from that surface? I know approximates to 1/r^3, but 1/0.001^3 =...
11. ### Satellites and the Earth's Magnetic Field

So i was just wondering if a satellite's circuitry could be affected by the Earth's own magnetic field inducing a current, if it was moving through it quickly enough (the space station for example), and how it might mess with it? Also considering a satellite is a big hunk of metal, could passing...
12. K

### Error analysis E/M experiment -- help please

So I am doing the charge to mass experiment and determining the relationship between: 1. accelerating voltage and radius formed by the electron beam 2. magnetic field strength and radius formed by electron beam Theoretically I should obtain an equation of the form: r = (1/B) *sqrt(2mV/e) where...
13. P

### Magnetism: magnetic feild strength of a wire

Homework Statement A wire 1.0 mm in diameter carries 5.0 A distributed uniformly over its cross section. a) Find the field strength 0.10 mm from its axis. b) Find the field strength at the wire’s surface Homework EquationsThe Attempt at a Solution I've used the Biot-Savart Law for a wire for...
14. C

### Comparing Magnetic Field Strengths with Vectors

Homework Statement Homework EquationsThe Attempt at a Solution Shouldn't they be the same? Does one being above the current and the other being below make any difference? I know when there is a higher density of magnetic field lines, the magnetic field strength is greater, but in this case...
15. ### Calculating Magnetic Field Strength from FFT

Hello All, Briefly on the exposition; I'm an undergraduate assistant to a professor. We contribute to the Muon g-2 experiment in Fermilab, designing and optimizing the magnetic-measurement equipment. As you might imagine I utilize the Fourier Transform often to analyze data. The data I'm...
16. ### Relationship between emf and magnetic field strength

Homework Statement See image below. Homework Equations motional emf = induced voltage = B L v The Attempt at a Solution I thought the answer would be A since there's a direct relationship between EMF and magnetic field strength. The answer is D.
17. ### Distance of compass to wire based on magnetic field strength

Homework Statement As shown in Figure 1 below, a long, straight conducting wire is stretched horizontally directly above a magnetic compass, both of which are separated by distance d. When electrical current is not flowing through the wire, the compass needle points in a direction parallel with...
18. ### Magnetic field strength over distance

I want to know how does distance affect the magnetic field of a permanent magnet. I have read about the inverse square law and how it could apply to magnetic fields over growing distances, but doing so, I read about monopoles, which is a new concept to me. So, for the time being, I would like a...
19. ### Magnetic field strength for circular loop

When deriving the magnetic field strength due to a circular loop at some distance away from it's center (using Biot-Savart's law), why is the angle between ds and r 90 degrees? This is a youtube video with the derivation, see 5:55
20. ### Magnetic field strenght - confusion here

I'm not sure how magnetic field strenghts and dipoles work. I know that the strenght decreases by 1/r^3, but - isn't magnetic field strenght a constant inherent to the magnet? - if it is not constant, what is? - how is all this related to magnetic damping force?
21. ### Negative values of magnetic fields strength obtained?

Homework Statement We were asked to use a Hall probe (in units of Guass) to measure the magnetic field strength in 0.5 cm increments away from a wire carrying 4 A of current. As we got further and further away from the wire our B value got smaller and smaller. Eventually they became negative...
22. ### Electromagnet magnetic field strength

Homework Statement Homework Equations ##\oint_{C} Bd\ell = \mu I_{enc}, B_{normal}## continuous across boundary, ##H_{parallel}## continuous across boundary The Attempt at a Solution $$\oint_{C} Bd\ell = \mu I_{enc} \rightarrow B = \frac{\mu NI}{2\pi r}$$ Any help much appreciated. How...
23. ### Calculate force on Permanent Magnet near a Paramagnetic surface

Hello all, new here but plan to stick around for a while. I am currently trying to make a sensor that can detect if a material below it is paramagnetic. I believe paramagnetic is the proper term, but it needs to detect if the force exerted by permanent magnet is above a certain threshold. The...
24. ### Magnetic field strength at point P around a solenoid

I have a solenoid, Length L, number of turns N, ampers I Radius R I have a Point P(x,y,z) anywhere around said solenoid. How can I calculate the field strength at point P, note it is OUTSIDE the solenoid, and could be anywhere outside. Assume the origin is the center of the solenoid, let's...
25. ### What is the maximum height a magnet can hover in a magnetic levitating globe?

Layman speaking here.. I have for a while been interested in a small desk toy. It is a magnetic levitating globe. There is a doughnut shaped electromagnet at the base which according to the internet is a toroid. Within the globe sits a disc shaped neodymium magnet. The globe hovers barely a...
26. ### Hall Effect Probe for Measuring Magnetic Field Strength

Homework Statement In a probe that uses the Hall effect to measure magnetic fields, a 11-A current passes through a 1.33-cm-wide and 1.31-mm-thick strip of sodium metal. If the Hall emf is 2.42 μV, what is the magnitude of the magnetic field (take it perpendicular to the flat face of the...
27. ### Finding the magnetic field strength

Homework Statement There exists a current of 5A in the ay direction at x=2m,z=-2m where the ay is the unit vector in the y direction. Find the magnetic field strength at the origin. Homework Equations B = (μI/2πR) * r B = μH The Attempt at a Solution B = (μI/2πr) B= (4π*10^-7)(5)/2π(2) where...
28. ### Could Earth's Early Magnetic Field Have Trapped Hydrogen in the Atmosphere?

could Earth's early magnetic field have been strong enough to trap hydrogen within the atmosphere?
29. ### Relationship between magnetic field strength and voltage

So I'm really confused with the relationship between magnetic field strength and voltage. Say you have a battery (with a DC voltage) with 4 coils, when voltage increases, does magnetic field strength increase? Is there any law (i.e. Faraday's law) that supports this?
30. ### Magnetic Field Strength Vs. Angle of direction

I have a simple question... does the magnetic field angle of direction vary when you vary the field strength? For example, say i have a magnetoresistive sensor, which, to my knowledge only detects the magnetic field angle of direction (unlike a halls, which senses field strength). I place...
31. ### Magnetic field strength that emits waves

Homework Statement The microwaves in a microwave oven are produced in a special tube called a magnetron. The electrons orbit the magnetic field at 2.99GHz, and as they do so they emit 2.99GHz electromagnetic waves. What is the magnetic field strength? Homework Equations ƒ=qβ/(2Pi*m) Thus...
32. ### Magnetic field strength and magnetic flux

Hi, please could someone help with my confusion over these two qauntities. In class we recently learned that magnetic field strength (B) is the number of flux lines (measured in Webers) per square metre. The magnetic flux on the other hand is the total number of flux lines (measured in Webers)...
33. ### Calculating how magnetic field strength decreases with distance

Hi everyone, I am trying to calculate the decrease in magnetic field strength over distance, using a formula I found on this thread https://www.physicsforums.com/showthread.php?t=522223 The formula given was 1/r^3, where r is the distance from the source. The same thread says the formula...
34. ### Ampere's Law - Magnetic Field Strength

Homework Statement Use Ampere's Law to show that the magnetic fi eld strength at a distance R from a long, straight wire, carrying a current I, is: H = I/2\piR Homework Equations F=qVB B=\mu0I/2\piR The Attempt at a Solution I'm not sure how to answer this question. I got the...
35. ### Magnetic Field Strength versus Coil Density

Homework Statement We did a lab where we measured the magnetic field strength of a wire coil versus the coil density of the wire coil, keeping current constant. We determined the relationship of B (magnetic field strength) versus n (coil density) to be direct. I need to explain why this is...
36. ### The magnetic field strength required to oscillate an electron

Homework Statement "An electron is accelerated by a potential difference of 1 V and is injected into vacuum. How strong should the magnetic field in a vacuum be if you want the electron to circle along a loop with a radius of 10^-1m? Please indicate the direction of the magnetic field"...
37. ### What is the maximum magnetic field strength for a given size permanent magnet?

Now I'm sure one can find this at google somehow , even though I wasn't that successful with it. Does someone know what is the highest magnetic field strength for a givem size permanent magnet for example? Like a 1cm ball of neodymium or some other material, what would be the highest field...
38. ### Calculating magnetic field strength through objects.

If I have a magnetic field of say 5 Tesla which is 3m from a concrete wall 0.25m thick how would I go about calculating the strength of the magnetic field on the other side of the wall? Any help/guidance much appreciated!
39. ### Relation Between the Magnetic Field Strength and Distance

Hey guys, I have recently performed a lab where we are to find the equation relating the magnetic field strength to a distance from a dipole in both the transverse and longitudinal direction. We did this using a Hall Effect Probe and a magnetic dipole. What I found after plotting a Log...
40. ### Magnetic field strength in hysteresis?

Hi, I have been reading about magnetic hysteresis and all sources refer to magnetic field strength (H) as having the units (A/m). Why is it just amps/meter and not ampere-turns/metre as H = NI/L and not N/L? Is there another equation for H that I am unaware of? Cheers.
41. ### Superconductor: Magnetic Field Strength VS distance

Hi all, Does anyone know how the magnetic field strength of a superconductor varies as distance from the outside of the superconductor? Aside from a superconductor being able to creates a stronger magnetic field than a regular dipole, does the strength still go down as 1/r^2 or does it...
42. ### Magnetic field strength in two wires

1. Multiple choice problem, the prompt is the following: Two wires carry currents is opposite directions, as shown below. The wires are separated by a distance of 0.02 meter, and points P and Q are located 0.01 meter above and below the bottom wire. Compare the Magnetic field strength at...
43. ### Electromagnetism, finding magnetic field strength

1. A 0.034 kg copper rod is hung by two wires and placed in a constant magnetic field. A current of 14 A runs through the 0.050 m long copper rod, making it hang at an angle of 34° from the vertical as attached in the diagram. What is the magnetic field strength holding the copper rod in...
44. ### Magnetic field strength infinitely long wire

I'm new to posting on this forum so excuse me if I'm using the wrong symbols underlined := vector/vectorfield δ := derivative uvar := unit vector Homework Statement Consider a finitely conducting wire of infinity length with radius b. The wire is centered about the z-axis. Current is...
45. ### Help Experiment determining the Earth's magnetic field strength

I am in my senior year of school and I have been given a research task to do on the Earth's magnetic field in a given place. I have to come up with a full method for the experiment to perform in class in a week or so and then I need to use equations to create a discussion and show how I found...
46. ### Measuring earth magnetic field strength

I'm somewhere at a suburb near Sydney and I have problems designing an experiment to measure the strength of the Earth magnetic field so that means now I'm close to geographic south and I'm close to magnetic north right? how do I measure the angles between the GS and Mn and what do I have to...
47. ### Calculating Magnetic Field Strength in a Balanced System

Homework Statement Homework Equations force = current * length * field strength * sin (theta) current = 5.6 A mass/ length = 80g/m right angles = sin(90) = 1 The Attempt at a Solution i noticed the mass is given in grams, 80 grams to be exact or .08 kg . how would I find the...
48. ### Find magnetic field strength and maximum force

Homework Statement Homework Equations Force = Current * Length * Field Strength * sin(theta) (Force/ Length)/(Current * sin theta) = Field Strength The Attempt at a Solution (.28 N/m)/ (14 A * sin 27 degree) = .044 T or 44mT
49. ### Why do different gauss meters measure magnetic field strength differently

I have used two different Gauss meters to measure the same NdFeB rare Earth N45 (45 MGOe) disc magnet (D28X6mm), with a Residual Induction (Br) of 1320-1380 mT. The first is a Dr. Steingroever GmbH FH51 Gauss meter. It would take readings of up to approximately 1.2 Tesla (12,000 Gauss)...
50. ### Find the current given length and magnetic field strength

Homework Statement What is the current in a long wire if the magnetic field strength 1.0 cm from the wire's axis is 55 mu T. i know magnetic field strength which is 1 cm i know the length which is 55 milli-tesla. I need to find Current in Amperes which is I. The chapter gives me the...