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   "source": [
    "# Chapter 12: Resistance and DC Circuits"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.1, Page 237"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Magnitude, I4 = -3 A\n"
     ]
    }
   ],
   "source": [
    "#Initialization\n",
    "i1=8                                 #current in Amp\n",
    "i2=1                                #current in Amp\n",
    "i3=4                                #current in Amp\n",
    "\n",
    "#Calculation\n",
    "i4=i2+i3-i1                                #current in Amp\n",
    "\n",
    "#Results\n",
    "print'Magnitude, I4 = %d A'%i4"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.2, Page 239"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "#Initialization\n",
    "e=12                   #EMF source in volt\n",
    "v1=3                   #node voltage\n",
    "v3=3                   #node voltage\n",
    "\n",
    "#Calculation\n",
    "v2=v1+v3-e                   #node voltage\n",
    "\n",
    "#Results\n",
    "print'V2 = %d V'%v2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.4, Page 242"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Voc = 10 V\n",
      "R = 100 ohm\n"
     ]
    }
   ],
   "source": [
    "import numpy as np\n",
    "\n",
    "#We have used method II for solving our problem by using simultaneous equations\n",
    "\n",
    "a = np.array([[25,-2],[400,-8]]) \n",
    "b = np.array([[50],[3200]])\n",
    "c=np.linalg.solve(a,b)\n",
    "\n",
    "print'Voc = %d V'%c[0]\n",
    "print'R = %d ohm'%c[1]\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.5, Page 244"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Voltage, V = 7.14\n"
     ]
    }
   ],
   "source": [
    "#Initialization\n",
    "r1=100                  #Resistance in Ohm\n",
    "r2=200                 #Resistance in Ohm\n",
    "r3=50                 #Resistance in Ohm\n",
    "v1=15                 #voltage source\n",
    "v2=20                 #voltage source\n",
    "\n",
    "#Calculation\n",
    "#Considering 15 V as a source & replace the other voltage source by its internal resistance,\n",
    "r11=(r2*r3)*(r2+r3)**-1              #resistance in parallel\n",
    "v11=v1*(r11/(r1+r11))               #voltage\n",
    "#Considering 20 V as a source & replace the other voltage source by its internal resistance,\n",
    "r22=(r1*r3)*(r1+r3)**-1              #resistance in parallel\n",
    "v22=v2*(r22/(r2+r22))               #voltage\n",
    "\n",
    "#output of the original circuit\n",
    "v33=v11+v22\n",
    "\n",
    "\n",
    "\n",
    "#Results\n",
    "print'Voltage, V = %.2f'%v33"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.6, Page 246"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Output Current, I = 1.67 A\n"
     ]
    }
   ],
   "source": [
    "#Initialization\n",
    "r1=10                  #Resistance in Ohm\n",
    "r2=5                  #Resistance in Ohm\n",
    "v2=5                 #voltage source\n",
    "i=2                 #current in Amp\n",
    "\n",
    "#Calculation\n",
    "#Considering 5 V as a source & replace the current source by its internal resistance,\n",
    "i1=v2*(r1+r2)**-1                   #current using Ohms law\n",
    "#Considering current source & replace the voltage source by its internal resistance,\n",
    "r3=(r1*r2)*(r1+r2)**-1              #resistance in parallel\n",
    "v3=i*r3                         #voltage using Ohms law\n",
    "i2=v3*r2**-1                   #current using Ohms law\n",
    "i3=i1+i2                       #total current\n",
    "\n",
    "#Results\n",
    "print'Output Current, I = %.2f A'%i3"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.8, Page 251"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "V2 = 33.04 V\n",
      "V3 = 43.15 V\n",
      "Current, I1 = 1.73 A\n"
     ]
    }
   ],
   "source": [
    "import numpy as np\n",
    "r=25                    #resistance in ohm\n",
    "\n",
    "#We have used for solving our problem by using simultaneous equations\n",
    "\n",
    "a = np.array([[(-13*60**-1),(1*20**-1)],[(1*60**-1),(-9*100**-1)]]) \n",
    "b = np.array([[-5],[-100*30**-1]])\n",
    "c=np.linalg.solve(a,b)\n",
    "i1=c[1]/r                        #required current\n",
    "\n",
    "print'V2 = %.2f V'%c[0]          #wrong answer in textbook\n",
    "print'V3 = %.2f V'%c[1]          #wrong answer in textbook\n",
    "print'Current, I1 = %.2f A'%i1\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Example 12.9, Page 253"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I1 = 326 mA\n",
      "I2 = 33 mA\n",
      "I3 = 53 mA\n",
      "Voltage, Ve = 0.197 V\n"
     ]
    }
   ],
   "source": [
    "import numpy as np\n",
    "re=10                 #resistance in ohm\n",
    "\n",
    "#We have used for solving our problem by using simultaneous equations\n",
    "\n",
    "a = np.array([[(-160),(20), (30)],[(20),(-210), (10)], [(30),(10), (-190)]]) \n",
    "b = np.array([[-50],[0],[0]])\n",
    "c=np.linalg.solve(a,b)\n",
    "ve=re*(c[2]-c[1])\n",
    "\n",
    "print'I1 = %d mA'%(c[0]*10**3)             #current I1\n",
    "print'I2 = %d mA'%(c[1]*10**3)              #current I2\n",
    "print'I3 = %d mA'%(c[2]*10**3)              #current I3\n",
    "print'Voltage, Ve = %.3f V'%ve\n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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    "collapsed": true
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