# 11: Magnetic properties¶

## Example number 11.1, Page number 11.3¶

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

#Variable declaration
M=1.4;     #magnetic field(T)
H=6.5*10**-4;  #magnetic field(T)

#Calculation
chi=M/H;
mew_r=1+chi;      #relative permeability of iron

#Result
print "relative permeability of iron is",int(mew_r)
print "answer given in the book is wrong"

relative permeability of iron is 2154
answer given in the book is wrong


## Example number 11.2, Page number 11.3¶

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

#Variable declaration
M=3300;     #magnetic field(amp/m)
H=220;  #magnetic field(amp/m)

#Calculation
chi=M/H;
mew_r=1+chi;      #relative permeability

#Result
print "relative permeability is",int(mew_r)

relative permeability is 16


## Example number 11.3, Page number 11.3¶

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

#Variable declaration
H=10**6;  #magnetic field(amp/m)
chi=1.5*10**-3;
mew0=4*math.pi*10**-7;

#Calculation
M=chi*H;     #magnetisation of material(A/m)
B=mew0*(M+H);     #flux density(T)

#Result
print "magnetisation of material is",M/10**3,"*10**3 A/m"
print "flux density is",round(B,4),"T"
print "answer given in the book varies due to rounding off errors"

magnetisation of material is 1.5 *10**3 A/m
flux density is 1.2585 T
answer given in the book varies due to rounding off errors


## Example number 11.4, Page number 11.4¶

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

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

#Calculation
M=chi*H;     #magnetisation of material(A/m)
B=mew0*(M+H);     #flux density(T)

#Result
print "magnetisation of material is",M,"A/m"
print "flux density is",round(B,4),"wb/m**2"

magnetisation of material is 37.0 A/m
flux density is 0.0126 wb/m**2


## Example number 11.5, Page number 11.13¶

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

#Variable declaration
I=500*10**-3;    #current(A)

#Calculation
A=2*math.pi*r**2;
mew_m=I*A;     #magnetic moment(Am**2)

#Result
print "magnetic moment is",round(mew_m*10**3,3),"*10**-3 Am**2"
print "answer given in the book varies due to rounding off errors"

magnetic moment is 7.854 *10**-3 Am**2
answer given in the book varies due to rounding off errors


## Example number 11.6, Page number 11.17¶

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

#Variable declaration
B=2;     #magnetic field(T)
e=1.602*10**-19;   #charge(c)
m=9.108*10**-31;    #mass(kg)

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

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

change in magnetic moment is 3.943 *10**-29 Am**2


## Example number 11.7, Page number 11.21¶

In [19]:
#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

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

susceptibility is 3.267 *10**-4


## Example number 11.8, Page number 11.27¶

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

#Variable declaration
Bs=0.65;      #magnetic induction(wb/m**2)
d=8906;       #density(kg/m**3)
mew0=4*math.pi*10**-7;
w=58.7;     #atomic weight(kg)

#Calculation
N=d*n/w;     #number of nickel atoms(per m**3)
mew_m=Bs/(N*mew0*9.27*10**-24);     #magnetic moment(mewB)

#Result
print "magnetic moment is",round(mew_m,2),"mewB"

magnetic moment is 0.61 mewB


## Example number 11.9, Page number 11.27¶

In [26]:
#importing modules
import math
from __future__ import division

#Variable declaration
mew=9.4*10**-24;
H=2;      #magnetic field(weber/m**2)
k=1.38*10**-23;     #boltzmann constant

#Calculation
T=2*mew*H/(math.log(2)*k);    #temperature(K)

#Result
print "temperature is",round(T,1),"K"

temperature is 3.9 K


## Example number 11.10, Page number 11.28¶

In [39]:
#importing modules
import math
from __future__ import division

#Variable declaration
d=7.8*10**3;    #density(kg/m**3)
n=6.025*10**26;    #number of atoms
w=157.26;     #atomic weight(kg)
mewm=9.27*10**-24;
mew=7.1*mewm;
mew0=4*math.pi*10**-7;

#Calculation
N=d*n/w;       #number of atoms
mew_B=N*mew/10**3;     #magnetic moment per gram(Am**2)
Bs=N*mew0*mew;

#Result
print "magnetic moment per gram",round(mew_B,3),"Am**2"
print "magnetic moment per gram is",round(Bs,4),"Wb/m**2"
print "answer given in the book varies due to rounding off errors"

magnetic moment per gram 1966.851 Am**2
magnetic moment per gram is 2.4716 Wb/m**2
answer given in the book varies due to rounding off errors


## Example number 11.11, Page number 11.42¶

In [41]:
#importing modules
import math
from __future__ import division

#Variable declaration
Tc=3.7;     #temperature(K)
Hc0=0.0306;    #critical field(T)
T=2;      #temperature(K)

#Calculation
Hc2=Hc0*(1-(T/Tc)**2);      #critical field(T)

#Result
print "critical field is",round(Hc2,5),"Tesla"

critical field is 0.02166 Tesla


## Example number 11.12, Page number 11.44¶

In [45]:
#importing modules
import math
from __future__ import division

#Variable declaration
Tc=7.18;     #temperature(K)
H0=6.5*10**4;    #critical field(T)
T=4.2;      #temperature(K)
d=1*10**-3;    #diameter(m)

#Calculation
Hc=H0*(1-(T/Tc)**2);      #critical field(T)
ic=math.pi*d*Hc;       #critical current(A)

#Result
print "critical current is",round(ic,2),"A"
print "answer given in the book is wrong"

critical current is 134.33 A
answer given in the book is wrong