# 20: Magnetic materials¶

## Example number 20.1, Page number 39¶

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration
M=2300;   #magnetisation(A/m)
B=0.00314;   #flux density(Wb/m**2)
mew0=4*math.pi*10**-7;

#Calculation
H=(B/mew0)-M;   #magnetizing force(A/m)
mew_r=(M/H)+1;  #relative permeability

#Result
print "magnetizing force is",round(H,4),"A/m"
print "relative permeability is",round(mew_r,5)

magnetizing force is 198.7326 A/m
relative permeability is 12.57334


## Example number 20.2, Page number 40¶

In [4]:
#importing modules
import math
from __future__ import division

#Variable declaration
H=10**4;   #magnetic field intensity(A/m)
chi=3.7*10**-3;   #susceptibility
mew0=4*math.pi*10**-7;

#Calculation
M=chi*H;   #magnetisation(A/m)
B=mew0*(M+H);   #flux density(Wb/m**2)

#Result
print "magnetisation is",M,"A/m"
print "flux density is",round(B*10**2,2),"*10**-2 Wb/m**2"

magnetisation is 37.0 A/m
flux density is 1.26 *10**-2 Wb/m**2


## Example number 20.3, Page number 41¶

In [7]:
#importing modules
import math
from __future__ import division

#Variable declaration
a=2.5*10**-10;   #interatomic spacing(m)
M=1.8*10**6;   #magnetisation(A/m)
n=2;   #number of atoms present in unit cell
e=1.6*10**-19;   #charge of electron(c)
m=9.1*10**-31;   #mass of electron(kg)
h=6.625*10**-34;   #planck's constant

#Calculation
nv=n/(a**3);   #number of atoms present per unit volume(per m**3)
Ma=M/nv;   #magnetisation produced per atom(A/m**2)
beta=e*h/(4*math.pi*m);   #bohr magneton(A/m**2)
Ma=Ma/beta;   #magnetisation produced per atom(bohr magneton)

#Result
print "average magnetisation produced per atom is",round(Ma,3),"bohr magneton"

average magnetisation produced per atom is 1.517 bohr magneton