MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics: 8.02 Electric Potential Game Consider two point-like charged objects with charges 1q Q= !, and 2q Q= + Question 1: Suppose the point P is located at (2 , )P a a=. Using only symmetry considerations (i.e. without calculation), predict the direction of the electric field. Question 2: Now move from (2 , )P a a= to (2 , 2 )S a a=. Without calculation answer the following: is the electric potential difference ( ) ( )V S V P! positive, zero, or negative? Why? Question 3: Which arrow most closely represents the direction of the electric field at (2 , 2 )S a a=? Part Two: Electric potential game. We next want you to look at an applet that shows you the electric potential due to two point charges, and how that is related to the electric field, using the examples from Part One above. We then want you to play a game where you explore bit by bit the electric potential due to two “invisible” point charges and guess the sign of the two invisible charges. You “win” the game by using the least number of moves to figure out what the signs of the charges are.Question 4: Open up the landscape applet. When you open the application you will see the charge configuration you were given in Question 1 above. We also show the potentials due to these two charges. You can explore the electric field by moving your avatar around the xy plane in the scene using the keypad on the right. The vertical distance of the avatar above the xy plane is the electric potential at the avatar’s location. We also show the electric field at the avatar’s location below the avatar in the xy plane. Using the application, confirm your answers to Questions (1), (2) and (3) above. Question 5: Using the same application as above, create a potential landscape using two positively charged objects, using the controls on the right to change the sign of the charges. Find a point on the landscape where the electric field points away from both charged objects. Briefly describe your strategy. Explore the region around your selected point and observe how the electric field changes direction. Move the charges around, and change their signs, to get an idea of what the potential landscape looks like for arbitrary placement of the charges and how the electric field varies as you move your avatar around the xy plane. You will need the intuition developed here to do well in the game below!! Question 5: Open up the electric potential game. You will have two charges which will be invisible, and located at random positions. You will only see that part of the electric potential that your avatar has explored. Move your avatar around the plane until you have enough information to guess the signs of the charges. Play the game and see which group at the table gets the lowest cumulative score for three
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