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Slide 2 Here we have an apple that is at a height h above the Earths surface. Slide 3 The apple has a potential energy equal to Slide 4 Anywhere along the dotted line the apple has the same height, therefore the same potential energy. Slide 5 Slide 6 Slide 7 This line that has the same potential is called an line. Slide 8 This line that has the same potential is called an line. Slide 9 For any object there is an infinite number of lines. Slide 10 Here we show some of the different lines. Slide 11 If we moved the apple along one of these lines Slide 12 there would be no change in potential energy therefore no work would be done. Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Slide 18 Slide 19 Slide 20 Slide 21 Slide 22 Slide 23 Slide 24 Slide 25 Slide 26 Slide 27 Slide 28 Slide 29 Slide 30 Slide 31 Once again, there was NO WORK done in moving the apple along the from point A to point B. Slide 32 We also know that if we raise an apple above the Earth and let it go, it will fall. Slide 33 Slide 34 Slide 35 Slide 36 Slide 37 Slide 38 The direction that the apple accelerates tells us the direction of the gravitational force. Slide 39 The direction of the gravitational force and the pattern of equilpotential lines give us a view of the. By Richard J. Terwilliger Slide 40 around the Earth. Slide 41 means that there will be a gravitational force on an object if it is placed in the field. Slide 42 Could this model also work with Slide 43 And how would we deal with two different net charges? Slide 44 Lets start with an object that has a NET NEGATIVE charge. Slide 45 Slide 46 Slide 47 Slide 48 Slide 49 Slide 50 Slide 51 Slide 52 Slide 53 Placing a test charge in the vicinity of this net negative charge and noticing if it experiences a force will tell us if there is an Electric Field around the charge. Slide 54 It will also tell us the direction of the Electric Field. Slide 55 The test charge is always defined as Slide 56 Therefore the test charge has a force acting on it the net negative charge. Slide 57 This is the direction of the Slide 58 Moving the test charge around the net negative Slide 59 and plotting the direction of the force will show us the field surrounding the charge. Slide 60 This positive test charge if free to move will fall towards the net negative charge. Slide 61 Slide 62 The positive test charge has no potential energy at this point. Slide 63 To pull the positive test charge away from the negative we must do work on the positive test charge. Slide 64 This work is equal to the potential energy at that point. Slide 65 So similar to the equipotentials surrounding the Earth, Slide 66 we have equal potentials surrounding the net negative charge. Slide 67 If the charge moves along the equipotential there is no work done. Slide 68 Slide 69 Slide 70 Slide 71 Slide 72 Slide 73 Slide 74 Slide 75 Slide 76 Slide 77 Slide 78 Slide 79 Slide 80 Slide 81 Slide 82 Slide 83 Slide 84 Slide 85 Slide 86 Slide 87 By Richard J. Terwilliger Slide 88 If the charge moves along the equipotential there is no work done. By Richard J. Terwilliger Slide 89 If the charge moves along the equipotential there is no work done. Slide 90 Slide 91 Slide 92 Slide 93 Slide 94 Slide 95 Slide 96 By Richard J. Terwilliger Slide 97 If the charge moves along the equipotential there is no work done. Slide 98 Slide 99 Slide 100 We now know the direction of the force and the pattern of equipotentials around the net negative charge. Slide 101 Notice the lines of force are at right angles to the equipotential lines. 90 o Slide 102 Slide 103 We can now predict the electric lines of force and the equipotential lines around a charge. Slide 104 A positive test charge placed near the net positive charge will experience a force outward. Slide 105 Therefore the electric field surrounding the net positive radiates out away from the positive. Slide 106 And the equipotential lines must cross these force lines at right angles forming concentric circles. Slide 107 Notice the force lines never cross each other and the equipotential lines never cross. Slide 108 So we now know what the fields look like around either a positive or negative charge Slide 109 Slide 110 What would the electric field lines and the equipotential lines look like around two charges? Slide 111 One negative and one positive. Slide 112 First we place our positive test charge in the field and determine the direction of the force on the test charge. Slide 113 The test charge is repelled away from positive and attracted toward the negative. Slide 114 Now move the test charge to a new position and determine the direction of the force. Slide 115 Keep moving the test charge and determine the direction of the force at each new position. Slide 116 Slide 117 If we place the test charge at the position shown, Slide 118 The test charge will experience a large force pushing it away from the positive charge and Slide 119 A very small force pulling it towards the negative charge. Slide 120 The electric field, at this point, would be the resultant of these two forces. Slide 121 Move the test charge and again find the resultant. Slide 122 Here the test charge is further away from the positive charge so the force is smaller. Slide 123 Move the test charge and again find the resultant force. Slide 124 Keep repeating until you have the pattern for the electric field line, the line of force. Slide 125 Once more. Slide 126 Connecting all of these arrows gives us the electric field line. Slide 127 From here we can finish the pattern. Slide 128 Now draw in the Remember, they never cross each other and must cross the force lines at right angles. Slide 129 Slide 130 Slide 131 Slide 132 Slide 133 Slide 134 Slide 135 Slide 136 Slide 137 Slide 138 Slide 139 Slide 140 Slide 141 Slide 142 Slide 143 Slide 144 Slide 145 Slide 146 Slide 147 Slide 148 Slide 149 What does the Electric Force lines and Equipotential lines look like between parallel plate charges? Slide 150 Slide 151 Lets check it out! Slide 152 First well start with two parallel plates. Slide 153 Next well charge one plate net negative and the other plate net positive. Slide 154 To determine the direction of the electric field well place the test charge between the plates. Slide 155 Remember the test charge? Slide 156 Is the test charge positive or negative? CLICK on YOUR ANSWER Slide 157 Hello? McFly! Slide 158 The electric field direction is determined using a net test charge Slide 159 Slide 160 A positive charge placed between the two parallel plates Slide 161 will be forced away from the positive plate and towards the negative plate. Slide 162 Slide 163 Slide 164 Slide 165 Slide 166 Slide 167 Slide 168 Slide 169 Slide 170 Slide 171 Slide 172 Slide 173 Slide 174 Slide 175 Slide 176 Slide 177 Slide 178 Slide 179 Slide 180 Slide 181 Slide 182 Slide 183 Slide 184 Slide 185 Slide 186 Slide 187 Slide 188 Slide 189 Slide 190 Slide 191 Slide 192 Slide 193 Slide 194 Slide 195 Slide 196 Slide 197 Slide 198 Slide 199 Slide 200 Slide 201 Slide 202 Slide 203 Slide 204 Slide 205 Slide 206 Therefore the electric field direction between two parallel charged plates is away from the positive plate and towards the negative plate. Slide 207 And the equipotential lines are perpendicular to the force lines. Slide 208