# Electromagnetic Induction

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Thread starter 2 months ago
#1
The following question is from b(ii)

How is magnetic flux linking the coil for a current of 3.5 A equal to B (flux density) at the centre of solenoid ×area of solenoid × N? Shouldnt it have been, flux linking the coil = magnetic flux intensity B at the centre of the solenoid × area of COIL × N?

Help would be highly appreciated, thanks!

I realise flux linkage = flux × N. But isnt flux calculated by multiplying the value of B by the area of the surface which it is linking/acting on? Instead of multiplying B by the area of the magnetic material producing that B.
Last edited by username5091846; 2 months ago
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2 months ago
#2
(Original post by crudux_c)
The following question is from b(ii)

How is magnetic flux linking the coil for a current of 3.5 A equal to B (flux density) at the centre of solenoid ×area of solenoid × N? Shouldnt it have been, flux linking the coil = magnetic flux intensity B at the centre of the solenoid × area of COIL × N?

Help would be highly appreciated, thanks!

I realise flux linkage = flux × N. But isnt flux calculated by multiplying the value of B by the area of the surface which it is linking/acting on? Instead of multiplying B by the area of the magnetic material producing that B.
Don’t forget that for a solenoid, the B field is mostly inside the coil acting parallel to the lengths of the cylinder that the coil creates.
So the area used in the CALC will be the circular cross section. Also the flux is perpendicular to this circular area so at a maximum of BAN without any trigonometric factor.
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Thread starter 2 months ago
#3
(Original post by swinroy)
Don’t forget that for a solenoid, the B field is mostly inside the coil acting parallel to the lengths of the cylinder that the coil creates.
Can you explain this again please?

Also, I still dont quite get why the area of solenoid is used to determine the flux linking the coil.
Last edited by username5091846; 2 months ago
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2 months ago
#4
(Original post by crudux_c)
Can you explain this again please?

Also, I still dont quite get why the area of solenoid is used to determine the flux linking the coil.
What area do YOU think should be used and why?
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Thread starter 2 months ago
#5
(Original post by swinroy)
What area do YOU think should be used and why?
I think area of coil should be used. From my understanding, I know the magnetic flux for anything is calculated by the product of magnetic flux intensity 'B' acting perpendicular to it and area.

We are calculating the flux in the coil, why use the area of solenoid? I'm aware that that's the only area given in the question so we don't have other option obviously, but I want to be able to understand the proper reasoning.
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2 months ago
#6
(Original post by crudux_c)
I think area of coil should be used. From my understanding, I know the magnetic flux for anything is calculated by the product of magnetic flux intensity 'B' acting perpendicular to it and area.

We are calculating the flux in the coil, why use the area of solenoid? I'm aware that that's the only area given in the question so we don't have other option obviously, but I want to be able to understand the proper reasoning.
Ok
Get the cardboard insert of a kitchen roll: It is a cylinder:look down on end of it and you are looking through a circular area A =pi r-squared
Wrap 20 turns of wire around the tube down the length and this is N = 20
Pass a current though this wire to produce a B field which acts down your eyeline along into the tube
The Flux Linkage is now BAN because
The B field is perpendicular to A
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