7: Magnetic properties

Example number 7.1, Page number 7.22

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

#Variable declaration
chi=-0.4*10**-5;      #magnetic susceptibility
H=5*10**5;      #magnetic field(A/m)
mew0=4*math.pi*10**-7;    

#Calculation
B=mew0*H*(1+chi);     #flux density(Wb/m**2)
M=chi*H;      #magnetic moment(A/m)

#Result
print "flux density is",round(B,3),"Wb/m**2"
print "magnetic moment is",M,"A/m"

flux density is 0.628 Wb/m**2
magnetic moment is -2.0 A/m

Example number 7.2, Page number 7.22

In [5]:
#importing modules
import math
from __future__ import division

#Variable declaration
chi=-0.25*10**-5;      #magnetic susceptibility
H=1000;      #magnetic field(A/m)
mew0=4*math.pi*10**-7;    

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

#Result
print "magnetisation is",M*10**2,"*10**-2 A/m"
print "flux density is",round(B*10**3,3),"*10**-3 Wb/m**2"

magnetisation is -0.25 *10**-2 A/m
flux density is 1.257 *10**-3 Wb/m**2

Example number 7.3, Page number 7.23

In [8]:
#importing modules
import math
from __future__ import division

#Variable declaration
H=250;      #magnetic field(A/m)
mewr=15;    #relative permeability
mew0=4*math.pi*10**-7;  

#Calculation
M=H*(mewr-1);      #magnetisation(A/m)
B=mew0*(H+M);     #flux density(Wb/m**2)

#Result
print "magnetisation is",M,"A/m"
print "flux density is",round(B*10**3,2),"*10**-3 Wb/m**2"

magnetisation is 3500 A/m
flux density is 4.71 *10**-3 Wb/m**2

Example number 7.4, Page number 7.23

In [10]:
#importing modules
import math
from __future__ import division

#Variable declaration
chi=-0.42*10**-3;      #magnetic susceptibility
H=1000;      #magnetic field(A/m)
mew0=4*math.pi*10**-7;    

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

#Result
print "magnetisation is",M,"A/m"
print "flux density is",round(B*10**3,3),"*10**-3 Wb/m**2"

magnetisation is -0.42 A/m
flux density is 1.256 *10**-3 Wb/m**2

Example number 7.5, Page number 7.23

In [13]:
#importing modules
import math
from __future__ import division

#Variable declaration
r=10/2;     #radius(cm)
i=500*10**-3;    #current(A)

#Calculation
mew=math.pi*(r*10**-2)**2*i;    #magnetic moment(Am**2)

#Result
print "magnetic moment is",round(mew*10**3,2),"*10**-3 Am**2"

magnetic moment is 3.93 *10**-3 Am**2

Example number 7.6, Page number 7.23

In [16]:
#importing modules
import math
from __future__ import division

#Variable declaration
mew0=4*math.pi*10**-7;    
B=0.0044;     #flux density(Wb/m**2)
M=3300;      #magnetic moment(A/m)

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

#Result
print "magnetizing force is",int(H),"A/m"
print "relative permeability is",round(mewr,1)
print "answer varies due to rounding off errors"

magnetizing force is 201 A/m
relative permeability is 17.4
answer varies due to rounding off errors

Example number 7.7, Page number 7.24

In [20]:
#importing modules
import math
from __future__ import division

#Variable declaration
r=0.052*10**-9;     #radius(m)
B=3;     #flux density(Wb/m**2)
e=1.6*10**-19;  
m=9.1*10**-31;    #mass(kg)

#Calculation
delta_mew=e**2*r**2*B/(4*m);     #change in magnetic moment(A m**2)

#Result
print "change in magnetic moment is",round(delta_mew*10**29,3),"*10**-29 Am**2"
print "answer given in the book is wrong"

change in magnetic moment is 5.705 *10**-29 Am**2
answer given in the book is wrong

Example number 7.8, Page number 7.24

In [24]:
#importing modules
import math
from __future__ import division

#Variable declaration
r=5.29*10**-11;     #radius(m)
B=2;     #flux density(Wb/m**2)
e=1.6*10**-19;  
m=9.1*10**-31;    #mass(kg)

#Calculation
d_mew=e**2*r**2*B/(4*m);     #change in magnetic moment(A m**2)

#Result
print "change in magnetic moment is",round(d_mew*10**29,3),"*10**-29 Am**2"

change in magnetic moment is 3.936 *10**-29 Am**2

Example number 7.9, Page number 7.24

In [27]:
#importing modules
import math
from __future__ import division

#Variable declaration
N=10**28;     #number of atoms(per m**3)
chi1=2.8*10**-4;   #susceptibility
T1=350;    #temperature(K)
T2=300;    #temperature(K)

#Calculation
chi2=chi1*T1/T2;    #susceptibility

#Result
print "susceptibility is",round(chi2*10**4,3),"*10**-4"

susceptibility is 3.267 *10**-4

Example number 7.10, Page number 7.25

In [30]:
#importing modules
import math
from __future__ import division

#Variable declaration
B=1.4;     #flux density(Wb/m**2)
B0=6.5*10**-4;    #magnetic field(Tesla)

#Calculation
mewr=B/B0;    #relative permeability

#Result
print "relative permeability is",round(mewr,2)

relative permeability is 2153.85