Flux = BAcosx (need help understanding this equation!)

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gay4justinbeiber
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k so here's my problem... from what i understand, flux is at its maximum when the area and flux density are perpendicular to each other (i.e. at an angle of 90 degrees or pi/2 radians).

but cos90 / cos(pi/2) = 0, so at right angles to each other the flux is 0.

should i trust the equation or the principle? or is there something i'm not seeing? lol..
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AnonyMatt
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Isn't flux = BANsinx? :l

EDIT: I'm totally lying. Ignore this post tbh.
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jaroc
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(Original post by gay4justinbeiber)
k so here's my problem... from what i understand, flux is at its maximum when the area and flux density are perpendicular to each other (i.e. at an angle of 90 degrees or pi/2 radians).

but cos90 / cos(pi/2) = 0, so at right angles to each other the flux is 0.

should i trust the equation or the principle? or is there something i'm not seeing? lol..
Let's right it in the vector form:

\Phi = \vec{B} \vec{A}.

In scalar form it is

\Phi = BA \cos \theta.

But here, \theta is the angle between surface normal and magnetic induction \vec{B}. Surface normal vector \vec{A} is actually perpendicular to the surface - so when magnetic induction \vec{B} is perpendicular to surface, the angle between the normal vector and magnetic induction vector is 0. \cos 0 = 1, so now you can trust both the equation and the principle
I hope this is clear enough. If not, try to read on the net about "surface normal" vector.
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Stonebridge
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(Original post by gay4justinbeiber)
k so here's my problem... from what i understand, flux is at its maximum when the area and flux density are perpendicular to each other (i.e. at an angle of 90 degrees or pi/2 radians).

but cos90 / cos(pi/2) = 0, so at right angles to each other the flux is 0.

should i trust the equation or the principle? or is there something i'm not seeing? lol..
Yes the flux passing through a coil is obviously maximum when it passes through the area such that the lines are perpendicular to the plane of the coil.
The angle in the formula BANcos theta is measured to a line that is perpendicular to the plane of the coil. So when they are perpendicular the angle is actually zero.
Cos theta = 1 and you get the maximum value.
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gay4justinbeiber
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(Original post by jaroc)
Let's right it in the vector form:

\Phi = \vec{B} \vec{A}.

In scalar form it is

\Phi = BA \cos \theta.

But here, \theta is the angle between surface normal and magnetic induction \vec{B}. Surface normal vector \vec{A} is actually perpendicular to the surface - so when magnetic induction \vec{B} is perpendicular to surface, the angle between the normal vector and magnetic induction vector is 0. \cos 0 = 1, so now you can trust both the equation and the principle
I hope this is clear enough. If not, try to read on then net about "surface normal" vector.
ah snap! just drew it out and i know exactly what the angle your talking about is!

thank you
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gay4justinbeiber
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(Original post by Stonebridge)
Yes the flux passing through a coil is obviously maximum when it passes through the area such that the lines are perpendicular to the plane of the coil.
The angle in the formula BANcos theta is measured to a line that is perpendicular to the plane of the coil. So when they are perpendicular the angle is actually zero.
Cos theta = 1 and you get the maximum value.
thanks again
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gay4justinbeiber
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(Original post by AnonyMatt)
Isn't flux = BANsinx? :l

EDIT: I'm totally lying. Ignore this post tbh.
prick.
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Magnalex
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I think what you don't understand is the difference between magnetic flux and magnetic field. Magnetic flux is the rate of change of magnetic field.Thus when the field passing through the coil is at a minimum, the rate of change of the field will be at a maximum. Flux = BAcos theta where B is the magnetic field. Helped any?
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Eimmanuel
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(Original post by jaroc)
Let's right it in the vector form:

\Phi = \vec{B} \vec{A}.

In scalar form it is

\Phi = BA \cos \theta.

But here, \theta is the angle between surface normal and magnetic induction \vec{B}. Surface normal vector \vec{A} is actually perpendicular to the surface - so when magnetic induction \vec{B} is perpendicular to surface, the angle between the normal vector and magnetic induction vector is 0. \cos 0 = 1, so now you can trust both the equation and the principle
I hope this is clear enough. If not, try to read on the net about "surface normal" vector.
I think magnetic flux is given by
\Phi = \vec{B} \cdot \vec{A}

instead of
\Phi = \vec{B} \vec{A}.

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Eimmanuel
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(Original post by Magnalex)
I think what you don't understand is the difference between magnetic flux and magnetic field. Magnetic flux is the rate of change of magnetic field.Thus when the field passing through the coil is at a minimum, the rate of change of the field will be at a maximum. Flux = BAcos theta where B is the magnetic field. Helped any?
Let assume a simple geometry first where the magnetic field lines are perpendicular to a surface and ignore the magnetic field B as vector quantity.
In this case, we can treat magnetic flux as magnetic field lines. Then magnetic field strB is the number of lines passing through the unit surface area.

 B = \dfrac{\text{number of magnetic field lines}} {A}

This "number of magnetic field lines" is the magnetic flux. So in the some of the elementary physics text, magnetic field strength is called magnetic flux density. They meant the same thing. But as you advance to higher level, we would differentiate magnetic field strength with magnetic flux density.

https://www.quora.com/What-is-the-ph...eld-strength-H

https://www.quora.com/Why-are-magnet...in-free-space#

Think of magnetic flux density B as the simple density concept.

 B = \dfrac{\Phi} {A} compare with  \rho = \dfrac{\text{m}} {V} .

So magnetic flux is like mass and surface area is like volume. And the magnetic flux density is like density (amount of matter(mass) contains in a unit volume).

Magnetic flux density is number of magnetic field lines passing through a unit area.

Hope it helps.
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Bumbie
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Kindly Help. How do u calculate magnetic flux through a coil.A circular coil with 250 windings and radius 0,04m,is rotated clockwise inside a magnetic field with a strength of 3,2T
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Yash Gupta
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Great
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swinroy
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(Original post by Bumbie)
Kindly Help. How do u calculate magnetic flux through a coil.A circular coil with 250 windings and radius 0,04m,is rotated clockwise inside a magnetic field with a strength of 3,2T
Flux = BAN
B = 3.2
A = circular area using pi r- squared
N= 250
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