# Chapter 10:The Solid state¶

## Example 10.1,Page no:342¶

In [2]:
#Variable declaration
import math
Ro= 0.281  #equilibrium distance between ions, nm
n= 9  #exponent, from observed compressibilities of NaCl
e= 1.6*(10**(-19))  #charge of an electron, C
Po= 8.85*(10**(-12))  #Permittivity of free space, F/m

#Calculation
K=1.0/(4*(math.pi)*Po)  #constant, N.m**2/C**2
Uo= -(K*alpha*(e**2)*(1.0-(1.0/n)))/(Ro*(10**(-9)))  #Potential energy per ion pair, J
Uo= Uo/e  #converting to eV
E1= 5.14  #Ionisation energy for Na, eV
E2= -3.61  #electron affinity of Cl, eV
E= E1+E2  #Electron transfer energy, eV
Ecohesive = (Uo +E)  #per electron pair, eV
Ecohesive= Ecohesive/2.0  #for each ion, eV

#Result
print"The cohesive energy in NaCl is: ",round(Ecohesive,2),"eV"
print"\nWhich is not far from experimental value of -3.28 eV"

The cohesive energy in NaCl is:  -3.21 eV

Which is not far from experimental value of -3.28 eV


### Example 10.2,Page no:350¶

In [3]:
#Variable declaration
A= 1.0  #cross-sectional area of wire, mm**2
I= 1.0  #current in wire, A
n= 8.5*(10**28)  # electrons/m**3
e= 1.6*(10**(-19))  #charge of an electron, C

#Calculation
Vdrift= I/(n*(A*(10**(-6)))*e)  #m/s

#Result
print"The drift velocity of electrons in the copper wire is:%.2g"%Vdrift,"m/s"
print"\nNOTE:Calculation mistake in book.Wrongly written as 7.4*10^-4"


The drift velocity of electrons in the copper wire is:7.4e-05 m/s

NOTE:Calculation mistake in book.Wrongly written as 7.4*10^-4


### Example 10.3,Page no:353¶

In [4]:
#Variable declaration
n= 8.48*(10**28)  #free electron density, m**(-3)
Vfermi= 1.57*(10**6)  #Fermi Velocity, m/s
rho= 1.72*(10**(-8))  #resistivity, ohm
e= 1.6*(10**(-19))  #charge of an electron, C
Me= 9.1*(10**(-31))  #mass of electron, kg

#Calculation
lamda= Me*Vfermi/(n*(e**2)*rho)  #m
lamda= lamda*(10**9)  #converting to nm

#Result
print"The mean free path is:",round(lamda,1),"nm"

The mean free path is: 38.3 nm