Anyone able to calculate flux density?

Something Else

Something Else

Something Else

Soldato
Joined
19 Feb 2012
Posts
4,409
I'm trying to work out the flux density of an electromagnet and I'm stuck.

The question is as follows

"An electromagnet has a cross section as shown (see below). If the flux produced by the electromagnet is 2mwb calculate the flux density in the cross section

482750_10151585796130864_337110316_n.jpg


as you can see ive got as far as working out the area. its all in millimeters and its 10x10mm,
I don't expect anyone to give me the answer on a plate but if anyone can show me the steps to work it out then id be very grateful.
 
Smells like homework to me!

Anyway...

Wikipedia says that the units of flux density are Wb/m^2. Therefore, divide the flux value that you have by the area that you have.

However, you might want to double check those area calculations ;)
 
Err...i hope i'm not over simplifying this but surely it's just total flux divided by area? Units should probably be mwb/m^2
 
I have gotten this far working it out.

magnetic flux density is measured in tesla's

Φ= magnetic flux passing through a certain area and measured in webers
B= The magnetic flux density in tesla
A= The area, at right angles to the flux through which the magnetic flux passes

so i want B so the formula is

Φ÷A

so this should be 2÷100

now im confused again as i think i need to factor in that 100mm is area so its sqaured


also i think that the rounded corners will affect the flux density or is that just the flux pattern they have an effect on?

cheers for the help

and yea its sort of homework but not school. City and Guilds electrical qualification
 
You need to remember to standardise your units.

Φ base unit is in kg m2 s-2 A-1
B base unit is in kg s-2 A-1

So you need to make sure your factor in your area as m2 eg. 100 x 10-6 m2

/Salsa

Edit: Stupid forum cant type in scientific notation. Looks so messy but you get the idea :mad:
 
Somthing Else said:
thats where i fell down i think. because everything was in milli i assumed that maybe i didnt need to use it but i think i was wrong. thank you
Click to expand...

You're welcome :)

I think you are also correct in that the round corners will not affect flux density but will affect flux pattern. I am by no means an expert however so dont take my word as gospel ;)

/Salsa
 
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Flux density = total flux/area

Total flux = 2mwb = 0.002wb

Area = Middle (10X10) = 100mm2 = 0.1m2
(Two ends are just a circle)
+ Ends πr2 = (5X5)x3.142 = 78.54mm2 = 0.07854m2

Total Area = 0.17853m2

Total = 0.002wb(flux)/0.17854m2(area) = 0.0112 Tesla (11.2mT)

Sure someone will check it, and say it wrong. ( was wrong inverted area and flux by mistake) I think you may have doubled the area of the ends?)
 
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