PHYC202 Cuyamaca College Just answer the questions

Names Group Date Lab 4: Electric Fields Contents: I. Introduction ………….………………………………………………………… II. Field of a Point Charge……………………………………………………….. III. Multiple Charges………………………………………………………………. IV. Electric Field Hockey…………………………………………………………. V. Conclusions……………………………………………………………………. 1 2 5 8 9 I. Introduction Purpose As you probably noticed from the electrostatics lab, sometimes it’s pretty hard to get precise, consistent charges that stay where you want them, so in this lab we will be using our fancy computers to simulate charges and their fields in order to gain a more intuitive understanding of Electric Fields. You’ll then use all this awesome knowledge to play a video game. By the end of this lab you should be able to: • Determine the relationship between electric field, charge and distance for a point charge. • Determine the relationship between electric Field strength in a region. Materials/Equipment Computer Charges and Fields simulator Electric Hockey simulator Tips • Remember how to use excel to plot stuff. II. Field of a point charge A. QUALITATIVE Procedure 1. Open Charges and Field simulation https://phet.colorado.edu/en/simulation/chargesand-fields and click Run Now. 2. Once the simulation opens, check the boxes next to grid and values. 3. Place a 1 nC positive point charge in the middle of the screen. 4. Place a few electric field sensors around the charge Questions 1. The length of the arrow corresponds to the strength of the E-field. Where do you put the sensors to get the longest arrows? The shortest arrows? 2. On the left, draw a picture of the electric field in vector form for this positive 1 nC charge. On the right, predict what the electric field in vector form would look like for a 1 nC negative charge. 3. Test your prediction for the negative point charge using the simulation. Were you correct? Why or why not? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 2 B. QUANTITATIVE Relationship between distance and electric field 1. Based only on your observations from the previous section, what would you guess the mathematical relationship is between the distance from a point charge and electric field strength? 2. Using the ruler tool and the electric fields sensors, find the electric field at 10 different distances from the charge and enter them in the table below. Distance Electric Field Strength 3. Plot these points in excel and find the appropriate trendline. Make sure to label your axes and units and put the equation on the graph. Print the graph as a whole page and attach it to your lab. 4. Based on your graph, what is the mathematical relationship between distance from a point charge and its electric field strength? Did you predict correctly in question 1? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 3 Relationship between charge and electric field 1. Based only on your observations from the previous section, what would you guess the mathematical relationship is between charge and electric field strength? 2. Using the ruler tool and an electric field sensor you leave in one place, find the electric field strength as you add more and more charges and enter your data in the table below. Charge Electric Field Strength 3. Plot these points in excel and find the appropriate trendline. Make sure to label your axes and units and put the equation on the graph. Print the graph as a whole page and attach it to your lab. 4. Based on your graph, what is the mathematical relationship between charge and it electric field strength? Did you predict correctly in question 1? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 4 III. Multiple Charges Predict and observe the electric field vectors for two equal charges. 1. What pattern would you expect for the electric field produced by a pair of charges which are equal in size and have the same sign? (Do not set up the simulation until after you have made your prediction!) Draw your prediction of the electric field directional arrows you would expect. Show at least a dozen arrows at evenly spaced intervals covering the entire area of the box, including the area between the charges. 2. Check your prediction. a. In what ways is the pattern similar to your prediction? In what ways is it different? b. Looking at the simulation, where is the field strongest? Where is it weakest? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 5 Predict and observe the electric field vectors for two opposite charges. 3. What pattern would you expect for the electric field produced by a pair of charges which are equal in size and have the opposite sign? (Do not set up the simulation until after you have made your prediction!) Draw your prediction of the electric field directional arrows you would expect. Show at least a dozen arrows at evenly spaced intervals covering the entire area of the box, including the area between the charges. 4. Check your prediction. c. In what ways is the pattern similar to your prediction? In what ways is it different? d. Looking at the simulation, where is the field strongest? Where is it weakest? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 6 Make up your own charge distribution and predict the electric field lines. 1. Clear the screen and set up an arbitrary charge distribution (Do not set up the simulation until after you have made your prediction!) Draw your prediction of the electric field directional arrows you would expect. Show at least a dozen arrows at evenly spaced intervals covering the entire area of the box, including the area between the charges. 2. Check your prediction. e. In what ways is the pattern similar to your prediction? In what ways is it different? f. Looking at the simulation, where is the field strongest? Where is it weakest? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 7 IV. Electric Field Hockey A. SET UP: 1. Open Charges and Field simulation http://phet.colorado.edu/en/simulation/legacy/electric-hockey and click Run Now. 1. Play with the game on the practice level to figure out how it works. 2. Two additional rules: • no charges may be placed inside the goal or directly behind it • no charge may be placed directly on top of or next to another charge to cancel out its effect B. PLAY: 1. First, complete a level 1 game, adding only 2 charges. When you have a setup that works, show it to the instructor. Then print out the display. 2. Next, complete a level 2 game, adding no more than 5 charges. Print out the display. 3. Finally, complete a level 3 game, if you can’t, at least show the instructor you you have made 50 attempts. 4. Attach the printouts of your three successful games to the lab before turning it in. Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 8 V. CONCLUSIONS 1. Based on your results from part II (field of a point charge) and without looking it up, please guess a mathematical relationship (you do not need specific numbers or constants, just an approximate proportionality) between electric field, charge and distance from a charge. Justify your answer in a couple sentences. 2. How does the equation you came up with in question 1 relate to Coulomb’s Law for ! ! force between two point charges (remembering that Coulomb’s Law is 𝐹⃑ = 𝑘 “! ” ” 𝑟̂ )? Give a relationship between E and F and justify your answer. 3. How is an electric field different from a gravitational field? 4. Can gravity be shielded? Why or why not? What about electric fields? Why or why not? Physics 200 Spring 2015 ©Miriam Simpson, Cuyamaca College 9

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