7: Magnetic Properties

Example number 1, Page number 7-22

In [3]:
#importing modules
import math
from __future__ import division

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

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

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

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

Example number 2, Page number 7-22

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

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

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

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

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

Example number 3, Page number 7-23

In [12]:
#importing modules
import math
from __future__ import division

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

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

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

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

Example number 4, Page number 7-23

In [15]:
#importing modules
import math
from __future__ import division

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

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

#Result
print "magnetisation is",M,"A/m"
print "magnetic flux density is",round(B*10**3,4),"*10**-3 wb/m**2"
print "answer for flux density in the book varies due to rounding off errors"

magnetisation is -0.42 A/m
magnetic flux density is 1.2561 *10**-3 wb/m**2
answer for flux density in the book varies due to rounding off errors

Example number 5, Page number 7-23

In [17]:
#importing modules
import math
from __future__ import division

#Variable declaration
d=0.1;             #diameter(m)
i=0.5;             #current(ampere)

#Calculation
r=d/2;            #radius of atom(m)
mew=i*math.pi*r**2;     #magnetic moment(A-m**2)

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

magnetic moment is 3.93 *10**-3 A-m**2

Example number 6, Page number 7-23

In [25]:
#importing modules
import math
from __future__ import division

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

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

#Result
print "magnetising force is",round(H,1),"A/m"
print "relative permeability is",round(mewr,2)
print "answers given in the book are wrong"

magnetising force is 201.4 A/m
relative permeability is 17.38
answers given in the book are wrong

Example number 7, Page number 7-24

In [28]:
#importing modules
import math
from __future__ import division

#Variable declaration
r=0.52*10**-10;     #radius(m)
B=3;     #magnetic induction(web/m**2)
e=1.6*10**-19;      #charge(c)
m=9.1*10**-31;      #mass(kg)

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

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

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

Example number 8, Page number 7-24

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

#Variable declaration
r=5.29*10**-11;     #radius(m)
B=2;     #magnetic induction(web/m**2)
e=1.6*10**-19;      #charge(c)
m=9.1*10**-31;      #mass(kg)

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

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

change in magnetic moment is 3.936 *10**-29 A-m**2

Example number 9, Page number 7-24

In [32]:
#importing modules
import math
from __future__ import division

#Variable declaration
chi1=2.8*10**-4;       #susceptibility
T1=350;                #temperature(K)
T2=300;                #temperature(K)

#Calculation
chi2=(chi1*T1)/T2;     #susceptibility at 300K

#Result
print "susceptibility at 300K is",round(chi2*10**4,3),"*10**-4"

ssusceptibility at 300K is 3.267 *10**-4

Example number 10, Page number 7-25

In [34]:
#importing modules
import math
from __future__ import division

#Variable declaration
B0=6.5*10**-4;       #magnetic field(Tesla)
B=1.4;               #magnetic field(Tesla)

#Calculation
mewr=B/B0;           #relative permeability of iron

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

relative permeability of iron is 2153.85