Math Help

Hi All,

I am trying to cacalculate the strength of electromagnets.

After some searching i have found the equations but i just can't quite get a handle on some of it?

They have an iron core C shaped electromagnet 15cm long & 1cm square in area with a 1cm air gap & the permeability of air is 1 in this example.


They write: The reluctance of the air gap is 1 centimeter divided by 1 times 1 square centimeter.

The answer they have is 100 henries per meter.

(1 centimeter) / (1 * 1 (square centimeter)) = 100 m-1

How do they calculate this to get 100 as the answer?

I noticed that Reluctance is in Henries per Meter but the above calculation is in Centimeters so i assume the answers i have been getting are actually Henries per Centimeter, do i simply multiply the answer by 100 to change it to meters & then the answer is in Henries per meter & seem correct?.

Any help will be greatly appreciated

Burnt said:

Hi All,
The answer they have is 100 henries per meter.

(1 centimeter) / (1 * 1 (square centimeter)) = 100 m-1

How do they calculate this to get 100 as the answer?

Click to expand...

Have you tried converting into meters before you do the calculation?

Mike.

Burnt said:

They write: The reluctance of the air gap is 1 centimeter divided by 1 times 1 square centimeter.

The answer they have is 100 henries per meter.

How do they calculate this to get 100 as the answer?

Click to expand...

With this \/ you can convert mm/sec to miles/days

Dimensional analysis - Wikipedia, the free encyclopedia

Normally we would calculate reluctance R like this:

R=L/(u0*ur*A)

where

R is reluctance (1/h)
L is length (m)
u0 is magnetic space constant (h/m)
ur is relative permeability
A is area (m*m)

and we would get 79577471.5 (1/h),

but apparently here they want to use instead:

R=L/(ur*A)

with same definitions as above except R has different dimension.

Proceeding with the calculation, we'll first convert to meters and sq. meters:

L=0.01 meters
A=0.0001 square meters

Using the formula now,

R=0.01/(1*0.0001)=100 in units of 1/m which might be called h/m.

To use this we'd have to include the u0 constant:

R=100/(4*pi*10^-7)=79577471.5 in units of (1/h)

Thank you MrAl & all for there comments.

Your help is greatly appreciated.

Thanks Again