# Find flux density

1. Aug 10, 2009

### circuitaki

an iron ring of mean length 5 cma has an air gap of 1mm and a winding of 200 turns. If the permeability of iron is 300 when 1A current flows through the coil find the flux density.

kindly help how I would drive it

2. Aug 10, 2009

### Staff: Mentor

Welcome to the PF. Try listing the Relevant Equations for this type of problem. There is an analogy with resistive circuits, where the current is determined by the driving voltage and the sum of the resistances in the circuit. Can you state whqt the analogous equations are for a magnetic circuit like this one?

3. Aug 11, 2009

### circuitaki

hi dear,

there is no person to help me in this

4. Aug 11, 2009

### Staff: Mentor

http://en.wikipedia.org/wiki/Magnetic_circuit

We can offer tutorial hints here (as I have done above), but we do not do the work for you.

What class is this for? What learning resources do you have from the class?

5. Aug 11, 2009

### circuitaki

hi dear,

MMF = Ni

B= $$\mu$$H

$$\mu$$ = $$\mu$$r$$\mu$$o

$$\mu$$NA

H = Ni/Length

6. Aug 11, 2009

### bm0p700f

I am not to sure what is meant by the air gap of 1mm. Also the mean length of the iron ring? It that the diameter. Man this is poorly worded.

First all what does flux density mean? How do you think you are going to calculate using the information you are given?

7. Aug 11, 2009

### Staff: Mentor

That's how this type of air-gap transformer/inductor problem is usually worded. The mean diameter is basically down the middle of the ring, so it's a 5cm ring with an air gap of 1mm (missing magnetic material).

8. Aug 11, 2009

### circuitaki

hi dear,

this is as as same worded as I have

9. Aug 11, 2009

### bm0p700f

That makes sense now.

10. Aug 11, 2009

### Staff: Mentor

So now you can solve your problem. Use the link I provided, and write out the equations for the reluctances and the other parts of the problem. Please show us your work as you solve for the flux...

11. Aug 11, 2009

### rootX

1) Find reluctances in the air gap and in the core
2) Find emf (or F)
3) Find flux
4) Find the flux denisty

I would leave it to you for finding all those formulas and relationships between reluctance, F, flux, and flux density.

Hint: You should already know this that you can build a electric circuit from above and treat F as V, flux as I and reluctance as R

12. Aug 11, 2009

### circuitaki

thank you root x I am at work at this moment as soon as Igo back I would perform it and then tell you thank you

13. Aug 12, 2009

### circuitaki

hi dear,

kindly guide me that here we found mmf or emf

14. Aug 12, 2009

### Staff: Mentor

Use the link in post #4, and rootX's hints in post #11, and show us your work in detail.

We will not do this problem for you. You have all that you need to work out the problem. Now show us your full work.

15. Aug 15, 2009

### circuitaki

Hi dear,,

how are you kindly help me the equation you tell me to drive for reluctance in this the area is not given and I have not know equation to drive it kidly help

16. Aug 15, 2009

### ideasrule

Call the area "A" and proceed with the calculation.

17. Aug 15, 2009

### circuitaki

hi dears but how can we put 2 unknown in a same equation for example for reluctance we need area S= l/ mu * A.

and same for flux weber= NI / l/munot *mur*A

18. Aug 18, 2009

### circuitaki

hi dear,

sory for late reply I was out of city as per your quidence I had put the area as A

now I have

total reluctance 24.3 A(area) AT/wb

H = 40.81 * 1o^2 AT/m

F = .5020 A(area) AT/m

now if I go to fine the E.M.F as per your guidence

i have this formula current*resistance=e.m.f

to find resistance I have R=conductance l/A

but still I have the problem of Area kindly help\me now with the equation from which I can find out the area

Kindly help me quickly I needed it urgent

19. Aug 19, 2009

### circuitaki

hi dears,

sorry for late reply acctualy I was out of city

as per your instructions I had put the area as a A

and I find out these total reluctance 24.3 A(area)AT/wb

magnetising force H = 40.81*10^2 AT/m

F = .5020 A(area) AT/wb

now to find out the flux or resistance agian I need the value of area which I have a problem

kndly help me with the equation with which I can find the area

20. Dec 11, 2011

### weird7

GIVEN:
L of Core=.5 m
Air Gap=10^3 m
N=200 turns
Permeability of iron(uFe)=300
I=1A
Uo=4pix10^-7
find B?

from uNI/L=B ;since B=Hu
therefore we have,NI=BL/u
NI(total)=NI(AIR)+NI(IRON)
(200)(1)=B(.5)/uFexU0 + B(10^3)/u(air)xUo
solve for B;
B=.094247779 Wb/m^2

hope you learn it (from heart)
from Philippines