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   "source": [
    "# 1: Bonding in Solids"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example number 1, Page number 1.21"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "-2*a/r**3 + 90*b/r**11\n"
     ]
    }
   ],
   "source": [
    "#importing modules\n",
    "import math\n",
    "from __future__ import division\n",
    "from sympy import *\n",
    "import numpy as np\n",
    "\n",
    "#Variable declaration\n",
    "n=1;\n",
    "m=9;\n",
    "a=Symbol('a')\n",
    "b=Symbol('b')\n",
    "r=Symbol('r')\n",
    "\n",
    "#Calculation\n",
    "y=(-a/(r**n))+(b/(r**m));\n",
    "y=diff(y,r);\n",
    "y=diff(y,r);\n",
    "\n",
    "#Result\n",
    "print y"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "young's modulus is 157 GPa\n"
     ]
    }
   ],
   "source": [
    "#since the values of a,b,r are declared as symbols in the above cell, it cannot be solved there. hence it is being solved here with the given variable declaration\n",
    "#importing modules\n",
    "import math\n",
    "from __future__ import division\n",
    "\n",
    "#Variable declaration\n",
    "a=7.68*10**-29;     \n",
    "r0=2.5*10**-10;    #radius(m)\n",
    "\n",
    "#Calculation\n",
    "b=a*(r0**8)/9;\n",
    "y=((-2*a*r0**8)+(90*b))/r0**11;    \n",
    "E=y/r0;           #young's modulus(Pa)\n",
    "\n",
    "#Result\n",
    "print \"young's modulus is\",int(E/10**9),\"GPa\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example number 2, Page number 1.22"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "effective charge is 0.72 *10**-19 coulomb\n",
      "answer given in the book is wrong\n"
     ]
    }
   ],
   "source": [
    "#importing modules\n",
    "import math\n",
    "from __future__ import division\n",
    "\n",
    "#Variable declaration\n",
    "dm=1.98*10**-29/3;      #dipole moment\n",
    "l=0.92*10**-10;         #bond length(m)\n",
    "\n",
    "#Calculation\n",
    "ec=dm/l;        #effective charge(coulomb)\n",
    "\n",
    "#Result\n",
    "print \"effective charge is\",round(ec*10**19,2),\"*10**-19 coulomb\"\n",
    "print \"answer given in the book is wrong\""
   ]
  }
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