initial commit / add all books

29 files changed, 454 insertions, 0 deletions

diff --git a/2258/CH7/EX7.1/7_1.sce b/2258/CH7/EX7.1/7_1.sce
new file mode 100755
index 000000000..5f91cbf25
--- /dev/null
+++ b/2258/CH7/EX7.1/7_1.sce
@@ -0,0 +1,21 @@
+clc();

+clear;

+// To calculate the number of electron hole pairs

+T1=300;    //temp in K

+T2=310;    //temp in K

+ni1=2.5*10^19;   //per cubic metre

+EgeV1=0.72;    //value of Eg in eV

+EgeV2=1.12;    //value of Eg in eV

+Eg1=EgeV1*1.6*10^-19;    //Eg in J

+Eg2=EgeV2*1.6*10^-19;    //Eg in J

+KB=1.38*10^-23;     //boltzmann constant in J/k

+//density of electron hole pair is ni = A*(T^(3/2))*exp(-Eg/(2*KB*T))

+// let (T^(3/2))*exp(-Eg/(2*KB*T)) be X

+X1=(T1^(3/2))*exp(-Eg1/(2*KB*T1));

+X2=(T2^(3/2))*exp(-Eg2/(2*KB*T2));

+//therefore ni1=A*X1 and ni2=A*X2. dividing ni2/ni1 we get X2/X1

+ni2=ni1*(X2/X1);

+printf("the number of electron hole pairs per cubic metre is");

+disp(ni2);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.10/7_10.sce b/2258/CH7/EX7.10/7_10.sce
new file mode 100755
index 000000000..9d7f50a1b
--- /dev/null
+++ b/2258/CH7/EX7.10/7_10.sce
@@ -0,0 +1,17 @@
+clc();

+clear;

+// To calculate the resistance

+l=1;    //length in cm

+l=l*10^-2;    //length in m

+e=1.6*10^-19;

+w=1;    //width in mm

+w=w*10^-3;    //width in m

+t=1;     //thickness in mm

+t=t*10^-3;      //thickness in m

+A=w*t;

+ni=2.5*10^19;

+mew_e=0.39;

+mew_p=0.19;

+sigma=ni*e*(mew_p+mew_e);

+R=l/(sigma*A);

+printf("resistance of intrinsic Ge rod is %f ohm",R);

diff --git a/2258/CH7/EX7.11/7_11.sce b/2258/CH7/EX7.11/7_11.sce
new file mode 100755
index 000000000..5600b38ae
--- /dev/null
+++ b/2258/CH7/EX7.11/7_11.sce
@@ -0,0 +1,21 @@
+clc();

+clear;

+// To calculate the conductivity

+Eg=1.1;   //energy gap in eV

+m=9.109*10^-31;

+k=1.38*10^-23;

+T=300;

+e=1.6*10^-19;

+h=6.626*10^-34;

+mew_e=0.48;     //electron mobility

+mew_h=0.013;    //hole mobility

+C=2*(2*%pi*m*k/(h^2))^(3/2);

+X=2*k*T/e;

+Y=-Eg/X;

+A=exp(Y);

+ni=C*(T^(3/2))*A;

+sigma=ni*e*(mew_e+mew_h);

+printf("conductivity in ohm-1 m-1 is");

+disp(sigma);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.12/7_12.sce b/2258/CH7/EX7.12/7_12.sce
new file mode 100755
index 000000000..7c49f7299
--- /dev/null
+++ b/2258/CH7/EX7.12/7_12.sce
@@ -0,0 +1,18 @@
+clc();

+clear;

+// To calculate the intrinsic carrier density and conductivity

+m=9.109*10^-31;

+k=1.38*10^-23;

+T=300;

+e=1.6*10^-19;

+h=6.626*10^-34;

+Eg=0.7;

+mew_e=0.4;     //electron mobility

+mew_h=0.2;    //hole mobility

+C=2*(2*%pi*m*k/((h^2)))^(3/2);

+X=2*k*T/e;

+ni=C*(T^(3/2))*exp(-Eg/X);

+sigma=ni*e*(mew_e+mew_h);

+printf("conductivity is %f ohm-1 m-1",sigma);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.13/7_13.sce b/2258/CH7/EX7.13/7_13.sce
new file mode 100755
index 000000000..9908f81e2
--- /dev/null
+++ b/2258/CH7/EX7.13/7_13.sce
@@ -0,0 +1,14 @@
+clc();

+clear;

+// To calculate the energy band gap

+k=8.616*10^-5;

+T1=20;    //temp in C

+T1=T1+273;    //temp in K

+T2=32;     //temp in C

+T2=T2+273;    //temp in K

+rho2=4.5;    //resistivity in ohm m

+rho1=2;    //resistivity in ohm m

+dy=log10(rho2)-log10(rho1);

+dx=(1/T1)-(1/T2);

+Eg=2*k*dy/dx;

+printf("energy band gap is %f eV",Eg);

diff --git a/2258/CH7/EX7.14/7_14.sce b/2258/CH7/EX7.14/7_14.sce
new file mode 100755
index 000000000..c80307335
--- /dev/null
+++ b/2258/CH7/EX7.14/7_14.sce
@@ -0,0 +1,15 @@
+clc();

+clear;

+// To calculate the temperature

+EgeV=1;   //energy in eV

+k=1.38*10^-23;

+Eg=EgeV*1.602*10^-19;    //in J

+//EF can be taken as (Ev+0.5)eV

+//therefore (Ev+0.5)eV = (Ec+Ev)/2--------(1)

+//let fermi level shift by 10% then (Ev+0.6)eV = ((Ec+Ev)/2)+((3*k*T/4)*log(4))-----(2)

+//subtracting (1) from (2)

+//0.1 eV = (3*k*T/4)*log(4)

+E=0.1;    //energy in eV

+E=E*1.602*10^-19;    //energy in J

+T=(4*E)/(3*k*log(4));

+printf("temperature is %f K",T);

diff --git a/2258/CH7/EX7.15/7_15.sce b/2258/CH7/EX7.15/7_15.sce
new file mode 100755
index 000000000..f32b21d0f
--- /dev/null
+++ b/2258/CH7/EX7.15/7_15.sce
@@ -0,0 +1,26 @@
+clc();

+clear;

+// To calculate the conductivity of intrinsic silicon

+ni=1.5*10^16;

+e=1.6*10^-19;

+mew_e=0.13;

+mew_h=0.05;

+sigma=ni*e*(mew_e+mew_h);

+printf("conductivity is %f ohm-1 m-1",sigma);

+M=28.1;    //atomic weight of Si

+d=2.33*10^3;   //density in kg/m^3

+v=M/d;

+N=6.02*10^26;

+N1=N/v;

+printf("number of Si atoms per m^3 is");

+disp(N1);

+//1 donor type impurity is added to 1 impurity atom

+ND=N1/(10^8);

+p=(ni^2)/ND;

+sigma_exd=ND*e*mew_e;

+printf("conductivity for donor type impurity is %f ohm-1 m-1",sigma_exd);

+//1 acceptor type impurity is added to 1 impurity atom

+Na=N1/(10^8);

+n=(ni^2)/Na;

+sigma_exa=Na*e*mew_h;

+printf("conductivity for acceptor type impurity is %f ohm-1 m-1",sigma_exa);

diff --git a/2258/CH7/EX7.16/7_16.sce b/2258/CH7/EX7.16/7_16.sce
new file mode 100755
index 000000000..75fdddabe
--- /dev/null
+++ b/2258/CH7/EX7.16/7_16.sce
@@ -0,0 +1,9 @@
+clc();

+clear;

+// To calculate the diffusion coefficient of electrons

+T=300;   //temperature in K

+KB=1.38*10^-23;

+e=1.6*10^-19;

+mew_e=0.19;    //mobility of electrons in m^2/Vs

+Dn=mew_e*KB*T/e;

+printf("diffusion coefficient of electrons is %f m^2/s",Dn);

diff --git a/2258/CH7/EX7.17/7_17.sce b/2258/CH7/EX7.17/7_17.sce
new file mode 100755
index 000000000..de2ce317e
--- /dev/null
+++ b/2258/CH7/EX7.17/7_17.sce
@@ -0,0 +1,11 @@
+clc();

+clear;

+// To calculate the Hall voltage

+RH=3.66*10^-4;     //hall coefficient in m^3/coulomb

+I=10^-2;    //current in amp

+B=0.5;    //magnetic field in wb/m^2

+t=1;    //thickness in mm

+t=t*10^-3;    //thickness in m

+VH=(RH*I*B)/t;

+VH=VH*10^3;    //converting from Volts to mV

+printf("Hall voltage is %f mV",VH);

diff --git a/2258/CH7/EX7.18/7_18.sce b/2258/CH7/EX7.18/7_18.sce
new file mode 100755
index 000000000..d6354859f
--- /dev/null
+++ b/2258/CH7/EX7.18/7_18.sce
@@ -0,0 +1,11 @@
+clc();

+clear;

+// To calculate the density and mobility of charge carrier

+RH=-7.35*10^-5;    //hall coefficient

+e=1.6*10^-19;

+n=(-1/(RH*e));

+sigma=200;

+mew=sigma/(n*e);

+printf("density of charge carriers in m^3 is");

+disp(n);

+printf("mobility of charge carriers is %f m^2/Vs",mew);

diff --git a/2258/CH7/EX7.19/7_19.sce b/2258/CH7/EX7.19/7_19.sce
new file mode 100755
index 000000000..bfa4bcfba
--- /dev/null
+++ b/2258/CH7/EX7.19/7_19.sce
@@ -0,0 +1,12 @@
+clc();

+clear;

+// To calculate the magnitude of Hall voltage

+I=50;    //current in amp

+B=1.5;   //magnetic field in T

+n=8.4*10^28;     //free electron concentration in electron/m^3

+t=0.5;    //thickness in cm

+e=1.6*10^-19;

+t=t*10^-2;    //thickness in m

+VH=(I*B)/(n*e*t);

+VH=VH*10^6;   //converting VH from V to micro V

+printf("magnitude of Hall voltage is %f microVolt",VH);

diff --git a/2258/CH7/EX7.2/7_2.sce b/2258/CH7/EX7.2/7_2.sce
new file mode 100755
index 000000000..dd3ab1a6f
--- /dev/null
+++ b/2258/CH7/EX7.2/7_2.sce
@@ -0,0 +1,15 @@
+clc();

+clear;

+// To calculate the charge carrier density and electron mobility

+RH=3.66*10^-4;   //hall coefficient in m^3/coulomb

+sigma=112;    //conductivity in ohm-1 m-1

+e=1.6*10^-19;

+ne=1/(RH*e);

+//sigma = e*ne*(mew_e+mew_h)

+//assuming mew_h = 0

+mew_e=sigma/(e*ne);

+printf("the charge carrier density per m^3 is");

+disp(ne);

+printf("electron mobility is %f m^2/Vs",mew_e);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.20/7_20.sce b/2258/CH7/EX7.20/7_20.sce
new file mode 100755
index 000000000..11778893a
--- /dev/null
+++ b/2258/CH7/EX7.20/7_20.sce
@@ -0,0 +1,11 @@
+clc();

+clear;

+// To calculate mew and n

+RH=3.66*10^-4;

+e=1.6*10^-19;

+rho_n=8.93*10^-3;

+n=1/(RH*e);

+mew_e=RH/rho_n;

+printf("n per m^3 is");

+disp(n);

+printf("mew_e is %f m^2/V",mew_e);

diff --git a/2258/CH7/EX7.21/7_21.sce b/2258/CH7/EX7.21/7_21.sce
new file mode 100755
index 000000000..104df520a
--- /dev/null
+++ b/2258/CH7/EX7.21/7_21.sce
@@ -0,0 +1,18 @@
+clc();

+clear;

+// To calculate the conductivity and equilibrium hole concentration

+mew_e=0.13;    //electron mobility in m^2/Vs

+mew_h=0.048;   //hole mobility in m^2/Vs

+ni=1.5*10^16;

+e=1.6*10^-19;

+T=300;   //temp in K

+ND=10^23;    //density per m^3

+sigmai=ni*e*(mew_e+mew_h);

+sigma=ND*mew_e*e;

+p=(ni^2)/ND;

+printf("conductivity of intrinsic Si is %f s",sigmai);

+printf("conductivity is %f s",sigma);

+printf("equilibrium hole concentration per m^3 is");

+disp(p);

+

+//answers for sigmai and sigma given in the book are wrong

diff --git a/2258/CH7/EX7.22/7_22.sce b/2258/CH7/EX7.22/7_22.sce
new file mode 100755
index 000000000..59e56de2c
--- /dev/null
+++ b/2258/CH7/EX7.22/7_22.sce
@@ -0,0 +1,22 @@
+clc();

+clear;

+// To calculate the forbidden energy gap

+T=300;   //temp in K

+kB=1.38*10^-23;

+mew_e=0.36;    //mobility of electrons in m^2/Vs

+e=1.6*10^-19;

+mew_h=0.7;    //mobility of electrons in m^2/Vs

+sigma=2.12;    //conductivity in ohm-1 m-1

+C=4.83*10^21;    //proportional constant

+ni=sigma/(e*(mew_e+mew_h));

+//exp(-Eg/(2*kB*T)) = (C*(T^(3/2)))/ni

+//let X be (C*(T^(3/2)))/ni

+X=(C*(T^(3/2)))/ni;

+//exp(-Eg/(2*kB*T)) = X 

+//applyinf log on both sides

+//Eg/(2*kB*T) = log(X)

+Eg=2*kB*T*log(X);

+printf("forbidden energy gap in eV is");

+disp(Eg);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.23/7_23.sce b/2258/CH7/EX7.23/7_23.sce
new file mode 100755
index 000000000..9e0ec3ba0
--- /dev/null
+++ b/2258/CH7/EX7.23/7_23.sce
@@ -0,0 +1,23 @@
+clc();

+clear;

+// To calculate the probability of occupation

+Eg=0.4;    //energy gap in eV

+Eg=Eg*1.6*10^-19;    //Eg in J

+KB=1.38*10^-23;

+T1=0;   //temp 1 in C

+T1k=T1+273;    //temp 1 in K

+T2=50;   //temp 2 in C

+T2k=T2+273;    //temp 2 in K

+T3=100;   //temp 3 in C

+T3k=T3+273;    //temp 3 in K

+//F(E) = 1/(1+(exp((E-Ep)/(KB*T))))

+//but E-Ep = (1/2)*Eg

+//therefore F(E) = 1/(1+(exp(Eg/(2*KB*T))))

+FE1=1/(1+(exp(Eg/(2*KB*T1k))));

+FE2=1/(1+(exp(Eg/(2*KB*T2k))));

+FE3=1/(1+(exp(Eg/(2*KB*T3k))));

+printf("probability of occupation at 0 C is %f eV",FE1);

+printf("probability of occupation at 50 C is %f eV",FE2);

+printf("probability of occupation at 100 C is %f eV",FE3);

+

+//answers given in the book are wrong

diff --git a/2258/CH7/EX7.24/7_24.sce b/2258/CH7/EX7.24/7_24.sce
new file mode 100755
index 000000000..1365aaad0
--- /dev/null
+++ b/2258/CH7/EX7.24/7_24.sce
@@ -0,0 +1,14 @@
+clc();

+clear;

+// To calculate the ratio between conductivity

+Eg=1.2;   //energy in eV

+Eg=Eg*1.6*10^-19;    //in J

+KB=1.38*10^-23;

+T1=600;   //temp in K

+T2=300;   //temp in K

+//sigma is proportional to exp(-Eg/(2*KB*T))

+//let sigma1/sigma2 be R

+R=exp((Eg/(2*KB))*((1/T2)-(1/T1)));

+disp(R);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.25/7_25.sce b/2258/CH7/EX7.25/7_25.sce
new file mode 100755
index 000000000..e08c114a7
--- /dev/null
+++ b/2258/CH7/EX7.25/7_25.sce
@@ -0,0 +1,16 @@
+clc();

+clear;

+// To calculate the resistivity of doped Ge

+ni=2.5*10^19;   //density of charge carriers in m^3

+r=1/(10^6);    //ratio

+e=1.6*10^-19;

+mew_e=0.36;   //mobility of electrons in m^2/Vs

+mew_h=0.18;   //mobility of holes in m^2/Vs

+N=4.2*10^28;    //number of Si atoms per m^3

+Ne=r*N;

+printf("number of impurity atoms per m^3 is");

+disp(Ne);

+Nh=(ni^2)/Ne;

+sigma=(Ne*e*mew_e)+(Nh*e*mew_h);

+rho=1/sigma;

+printf("the resistivity of doped Ge is %f ohm m",rho);

diff --git a/2258/CH7/EX7.26/7_26.sce b/2258/CH7/EX7.26/7_26.sce
new file mode 100755
index 000000000..286d01025
--- /dev/null
+++ b/2258/CH7/EX7.26/7_26.sce
@@ -0,0 +1,10 @@
+clc();

+clear;

+// To calculate the conductivity of material

+n=5*10^17;   //concentration in m^3

+vd=350;   //drift velocity in m/s

+E=1000;   //electric field in V/m

+e=1.6*10^-19;

+mew=vd/E;

+sigma=n*e*mew;

+printf("the conductivity of material is %f ohm m",sigma);

diff --git a/2258/CH7/EX7.27/7_27.sce b/2258/CH7/EX7.27/7_27.sce
new file mode 100755
index 000000000..7cfe809c3
--- /dev/null
+++ b/2258/CH7/EX7.27/7_27.sce
@@ -0,0 +1,9 @@
+clc();

+clear;

+// To calculate the concentration

+sigma_e=2.2*10^-4;   //conductivity

+mew_e=125*10^-3;    //mobility of electrons in m^2/Vs

+e=1.602*10^-19;

+ne=sigma_e/(e*mew_e);

+printf("concentration in m^3 is");

+disp(ne);

diff --git a/2258/CH7/EX7.28/7_28.sce b/2258/CH7/EX7.28/7_28.sce
new file mode 100755
index 000000000..52538a1e1
--- /dev/null
+++ b/2258/CH7/EX7.28/7_28.sce
@@ -0,0 +1,11 @@
+clc();

+clear;

+// To calculate the mobility and density of charge carrier

+RH=3.66*10^-4;    //hall coefficient in m^3/c

+rho_i=8.93*10^-3;    //resistivity in ohm m

+e=1.6*10^-19;

+nh=1/(RH*e);

+mew_h=1/(rho_i*nh*e);

+printf("density of charge carriers in m^3 is");

+disp(nh);

+printf("mobility of charge carriers is %f m^2/Vs",mew_h);

diff --git a/2258/CH7/EX7.29/7_29.sce b/2258/CH7/EX7.29/7_29.sce
new file mode 100755
index 000000000..8d35860df
--- /dev/null
+++ b/2258/CH7/EX7.29/7_29.sce
@@ -0,0 +1,20 @@
+clc();

+clear;

+// To calculate the Hall voltage and charge carrier concentration

+I=3;    //current in mA

+I=I*10^-3;    //current in amp

+e=1.6*10^-19;

+RH=3.66*10^-4;    //hall coefficient in m^3/C

+B=1;    //flux density in w/m^2

+d=2;   //dimension along Y in cm

+d=d*10^-2;   //dimension along Y in m

+z=1;   //dimension along z in mm

+z=z*10^-3;    //dimension along z in m

+A=d*z;   //area in m^2

+EH=RH*I*B/A;

+VH=EH*d;

+VH=VH*10^3;    //converting from V to mV

+n=1/(RH*e);

+printf("Hall voltage is %f mV",VH);

+printf("charge carrier concentration in m^3 is");

+disp(n);

diff --git a/2258/CH7/EX7.3/7_3.sce b/2258/CH7/EX7.3/7_3.sce
new file mode 100755
index 000000000..e81c5b276
--- /dev/null
+++ b/2258/CH7/EX7.3/7_3.sce
@@ -0,0 +1,17 @@
+clc();

+clear;

+// To calculate the conductivity of intrinsic silicon and resultant conductivity

+ni=1.5*10^16;   //intrinsic concentration per m^3

+e=1.6*10^-19;

+mew_e=0.13;    //mobility of electrons in m^2/Vs

+mew_h=0.05;    //mobility of holes in m^2/Vs

+ND=5*10^20;    //conductivity in atoms/m^3

+sigma1=ni*e*(mew_e+mew_h);

+nd=(ni^2)/ND;

+sigma2=ND*e*mew_e;

+NA=5*10^20;

+na=(ni^2)/NA;

+sigma3=NA*e*mew_h;

+printf("intrinsic conductivity of Si is %f ohm-1 m-1",sigma1);

+printf("conductivity of Si during donor impurity is %f ohm-1 m-1",sigma2);

+printf("conductivity of Si during acceptor impurity is %f ohm-1 m-1",sigma3);

diff --git a/2258/CH7/EX7.4/7_4.sce b/2258/CH7/EX7.4/7_4.sce
new file mode 100755
index 000000000..c0ffdde02
--- /dev/null
+++ b/2258/CH7/EX7.4/7_4.sce
@@ -0,0 +1,22 @@
+clc();

+clear;

+// To calculate the conductivity

+sigma1=2;    //conductivity in ohm-1 m-1

+EgeV=0.72;    //band gap in eV

+Eg=EgeV*1.6*10^-19;    //in J

+KB=1.38*10^-23;    //boltzmann constant

+T1=20;    //temp in C

+T1=T1+273;   //temp in K

+T2=40;    //temp in C

+T2=T2+273;   //temp in K

+//sigma2/sigma1 = exp((-Eg/(2*KB))*((1/T2)-(1/T1)))

+//by taking log on both sides we get 2.303*log10(sigma2/sigma1) = (Eg/(2*KB))*((1/T1)-(1/T2))

+//let (Eg/(2*KB))*((1/T1)-(1/T2)) be X

+X=(Eg/(2*KB))*((1/T1)-(1/T2));

+//let log10(sigma2/sigma1) be Y

+Y=X/2.303;

+//log10(sigma2/sigma1) = log10(sigma2)-log10(sigma1)

+//let log10(sigma2) be A

+A=Y+log10(sigma1);

+sigma2=10^A;

+printf("the conductivity is %f ohm-1 m-1",sigma2);

diff --git a/2258/CH7/EX7.5/7_5.sce b/2258/CH7/EX7.5/7_5.sce
new file mode 100755
index 000000000..7c5b96d01
--- /dev/null
+++ b/2258/CH7/EX7.5/7_5.sce
@@ -0,0 +1,20 @@
+clc();

+clear;

+// To calculate the concentration of holes and electrons 

+mew_n=1300*10^-4;   //in m^2/Vs

+mew_p=500*10^-4;   //in m^2/Vs

+sigma=3*10^4;   //conductivity in ohm-1 m-1

+e=1.6*10^-19;

+N=sigma/(e*mew_n);

+ni=1.5*10^16;    //per m^3

+p=(ni^2)/N;

+P=sigma/(e*mew_p);

+n=(ni^2)/P;

+printf("concentration of electrons in n-type per cubic metre are");

+disp(N);

+printf("concentration of holes in n-type per cubic metre are");

+disp(p);

+printf("concentration of electrons in p-type per cubic metre are");

+disp(n);

+printf("concentration of holes in p-type per cubic metre are");

+disp(P);

diff --git a/2258/CH7/EX7.6/7_6.sce b/2258/CH7/EX7.6/7_6.sce
new file mode 100755
index 000000000..e33546f43
--- /dev/null
+++ b/2258/CH7/EX7.6/7_6.sce
@@ -0,0 +1,10 @@
+clc();

+clear;

+// To calculate the resistivity

+ni=2.37*10^19;   //intrinsic carrier density per m^3

+mew_e=0.38;    //in m^2/Vs

+mew_n=0.18;    //in m^2/Vs

+e=1.6*10^-19;

+sigmai=ni*e*(mew_e+mew_n);

+rho=1/sigmai;

+printf("resistivity is %f ohm m",rho);

diff --git a/2258/CH7/EX7.7/7_7.sce b/2258/CH7/EX7.7/7_7.sce
new file mode 100755
index 000000000..292240261
--- /dev/null
+++ b/2258/CH7/EX7.7/7_7.sce
@@ -0,0 +1,14 @@
+clc();

+clear;

+// To calculate the position of fermi level

+Eg=1.12;   //band gap in eV

+K=1.38*10^-23;

+T=300;   //temp in K

+//EF = (Eg/2)+(3*K*T/4)*log(mh/me)

+//given me=0.12m0 and mh=0.28m0. therefore mh/me = 0.28/0.12 

+//let mh/me be X. therefore X=0.28/0.12 

+X=0.28/0.12;

+EF=(Eg/2)+((3*K*T/4)*log(X));

+printf("the position of fermi level is %f eV",EF);

+

+//answer given in the book is wrong

diff --git a/2258/CH7/EX7.8/7_8.sce b/2258/CH7/EX7.8/7_8.sce
new file mode 100755
index 000000000..db5de244a
--- /dev/null
+++ b/2258/CH7/EX7.8/7_8.sce
@@ -0,0 +1,17 @@
+clc();

+clear;

+// To calculate the concentration of intrinsic charge carriers

+KB=1.38*10^-23;

+T=300;   //temp in K

+h=6.626*10^-34;

+m0=9.11*10^-31;

+mh=m0;

+me=m0;

+EgeV=0.7;    //energy gap in eV

+Eg=EgeV*1.6*10^-19;    //in J

+A=((2*%pi*KB/(h^2))^(3/2))*(me*mh)^(3/4);

+B=T^(3/2);

+C=exp(-Eg/(2*KB*T));

+ni=2*A*B*C;

+printf("concentration of intrinsic charge carriers per cubic metre is");

+disp(ni);

diff --git a/2258/CH7/EX7.9/7_9.sce b/2258/CH7/EX7.9/7_9.sce
new file mode 100755
index 000000000..ff2bc987e
--- /dev/null
+++ b/2258/CH7/EX7.9/7_9.sce
@@ -0,0 +1,10 @@
+clc();

+clear;

+// To calculate the resistivity

+ni=2.4*10^19;

+mew_e=0.39;

+mew_h=0.19;

+e=1.6*10^-19;

+sigmai=ni*e*(mew_e+mew_h);

+rhoi=1/sigmai;

+printf("resistivity is %f ohm m",rhoi);