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+{
+ "metadata": {
+  "name": "CH21"
+ },
+ "nbformat": 3,
+ "nbformat_minor": 0,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "metadata": {},
+     "source": [
+      "Chapter 21: Optical Properties"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "Example 21.1 Page No 125"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "# Calculation of absorption coefficient\n",
+      "\n",
+      "#Given\n",
+      "# x is thickness of glass(mm)\n",
+      "x=200\n",
+      "#It is intensity of non-absorbed radiation\n",
+      "#Io is intensity of non-relected radiation\n",
+      "f=0.98  #f=It/Io\n",
+      "\n",
+      "#Calculation\n",
+      "#b is absorption coefficient\n",
+      "b=-math.log(f)/x\n",
+      "\n",
+      "#result\n",
+      "print\"Absorption coefficient is \",round(b,4),\"mm**-1\"\n",
+      "\n"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Absorption coefficient is  0.0001 mm**-1\n"
+       ]
+      }
+     ],
+     "prompt_number": 2
+    }
+   ],
+   "metadata": {}
+  }
+ ]
+}
+\ No newline at end of file