Electric Charge Field Online Jonathan

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Physics

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Feb 20, 2024

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Physics Lab (Online Simulation) Charges and Fields Introduction to Static Electricity Electricity and Light TA name: Pramanand Joshi Due Date: 2/9/23 Student Name: Student ID: This lab uses the Balloons and Static Electricity John Travoltage and Charges and Fields Remote lab simulation from PhET Interactive Simulations at University of Colorado Boulder, under the CC-BY 4.0 license. Learning Goals: Students will be able to A. Describe and draw models for common static electricity concepts. (transfer of charge, induction, attraction, repulsion, and grounding) B. Determine the variables that affect how charged bodies interact C. Predict how charged bodies will interact D. Describe the strength and direction of the electric field around a charged body E. Use free-body diagrams and vector addition to help explain the interactions F. Compare electric fields to gravitational fields Theory: An Electric Field is a region in space in which electric forces act on electric charges. The Electric Field strength for any point in space is defined as the net Electric (Coulomb) Force per unit of positive charge acting on a charge placed at that point, i.e., ⃗ E = ⃗ F q [1] The SI unit for electric field is Newton / coulomb (N/C), or (more practically) volt/meter, (V/m). The direction of an electric field at any point is defined as the direction of the net electric force on a positive charge placed at that point. Since, F = k q 1 q 2 /r 2 (Coulomb’s Law), the Electric Field can be written in the form E = kq/r 2 where r is the distance from the charge. Faraday introduced the concept of lines of force to aid in visualizing the magnitude and direction of the total electric field about a charge or collection of charges. These concepts are listed below. 1

Physics Lab (Online Simulation) 1. A line of force is everywhere tangent to the electric field direction. 2. The lines of force originate on positive charges and terminate on negative charges. 3 The density of the lines of force (i.e. the lines/cm or lines/cm 2 ) in a region of space is used to represent the electric field strength in that region of space. 4 Lines of force will not cross over or touch one another. Electric fields can be represented by a scaled drawing, by first choosing a scale factor (proportionality factor) so that n number of lines/cm 2 represent a certain value of field strength (volts/m). (b) (a) Figure 1 Examine the figure above. The two figures represent an electric field departing a charged sphere. If we let figure 1( a ) represent an electric field with field strength of E , figure 1( b ) would represent an electric field with field strength of 2 E . (Twice the numbers of field lines depart the charge). In this experiment, we may estimate the electric field at certain points from the potential gradient, at these points E =  V/  x = (V 2 – V 1 ) / (x 2 – x 1 ) [2] Where V 1 and V 2 are the potential of two adjacent equipotential lines and (x 2 – x 1 ) is the distance between the lines in meters. It is possible to find any number of points in an electric field, all of which are at the same potential (voltage). If a line or surface is constructed such that it includes all such points with equal potential, the line or surface is known as an equipotential line or surface An expenditure of work is required when moving a charge parallel to the direction of the electric field. To move between one equipotential line to another, an amount of work is required to satisfy the laws of conservation of energy. From mechanics it is known that W = F d. From equation [1] it can be found that F = q E. Therefore, the work to move a charge can be determined by combining the two equations to obtain W = q E d. However, when a charged is moved along an equipotential line or surface, it is moving in a direction perpendicular to the electric field and therefore no expenditure of work is needed to move the charge. 2

Physics Lab (Online Simulation) This pre-lab is worth 5 points. Type your ALL ANSWERS in BLUE 1) What is an electric field? Electron fields are a region of space around a body that is charged where electric forces are acting on electric charges. 2) What are the units for an electric field? List both of them. Newton/Coulomb (N/C) or volt/meter (V/m). 3) What is an equipotential line? A line that is constructed that includes all points with an equal amount of potential. 4) Lines of force originate on positive charges and terminate on negative charges. 5) Electric field lines are (parallel, perpendicular ) to the equipotential lines. 3

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Physics Lab (Online Simulation) Static Charges 1. Open Balloons and Static Electricity , then explore to develop your own ideas about electrical charge. Describe several of your experiments and your observation with captured images from the simulation. a. One balloon: Neutral balloon had no affect on the wall after being rubbed on the wall. After rubbing the balloon against the sweater to get some negative charges, the balloon moved slowly to the left towards the sweater and then got stuck to it. 4

Physics Lab (Online Simulation) I took the negative charges from the sweater and then rubbed the wall, the balloon repelled the negative charges. The balloon repelled the negative charges on the wall. b. Two balloons: When the two balloons have no negative charges, they were stationary. But if there was any amount of negative charges, the balloons travel to the sweater. When the balloons were on the wall, a wave formed due to the negative charges repelling each other. 5

Physics Lab (Online Simulation) c. Wall removed: With the wall removed, one balloon picked up little negative charges, but would still be attracted to the sweater. It would move towards the sweater very slow. Taking two balloons, one was given more charges than the other. The one with more negative charges moved towards the sweater while the other one moved away from the sweater. 2. Open John Travoltage , then explore to develop your own ideas about electrical charge. 6

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Physics Lab (Online Simulation) Describe several of your experiments and your observation with captured images from the simulation. a. It took me 12 swipes to build enough charge to move the charges to eventually shock the door handle. b. When I pointed his finger away and started rubbing his feet, nothing would exit from him. c. I wanted to see what would happen when the finger was pointed downwards. After rubbing enough to get charged, the shock would still leave the body. 7

Physics Lab (Online Simulation) Test your understanding: Without using the simulations, predict the answers to these questions, then use the simulation to check your ideas. Question 1. When the balloon is rubbed on the sweater, what might happen? What do you predict for the answer?  B Describe an experiment and include images from the simulation that supports your answer . I rubbed a normal balloon with no charges onto the sweater. It picked up negative charges, which makes answer B the best answer. 8

Physics Lab (Online Simulation) Question 2 . What do you think will happen when the balloon is moved closer to the wall? What do you predict for the answer?  A Describe an experiment and include images from the simulation that supports your answer . I took a normal balloon and then rubbed it against the sweater to charge it negatively. When I placed it on the wall, the negative charges in the wall was repelled. Question 3. What do you think the balloons will do? 9

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Physics Lab (Online Simulation) What do you predict for the answer?  B Describe an experiment and include images from the simulation that supports your answer. I made two negatively charged balloons by rubbing them on the sweater. When they were close together, they would repel each other. Question 4. What might happen to the charge on the man when he touches the doorknob? 10

Physics Lab (Online Simulation) What do you predict for the answer?  A Describe an experiment and include images from the simulation that supports your answer. It took me 4 swipes to get the negative charges even in each arm. The closer I got to the door, the charges were discharged immediately. Electric Charge/Field 1. Two balloons were rubbed on a sweater like in the Balloons and Static Electricity and then hung like in the picture below. Explain why you think they move apart and what might affect how far apart they will be. I think if two negatively charged balloons were close to one another, they would repel each other. Only opposite signs attract, so two of the same sign charges would repel each other. The more of the same amount of charges would mean more repelling power. 11

Physics Lab (Online Simulation) Explain your understanding: 2. Watch the short video demonstration of Electric Field Hockey. https://phet.colorado.edu/sims/cheerpj/electric-hockey/latest/electric-hockey.html a. Why can you make a goal without hitting the puck?  It’s possible to make goal. The puck is charged, so using another object that is charged the same as the puck would repel it towards the goal. b. Why can you use either a positive charge or a negative charge to move the positively charged puck?  Using different combinations of both positive and negative charges can lead to may outcomes that end in hitting the goal. c. What do you think would happen if you use 2 charges instead of one to make the puck move?  Using two charges instead of one would cause the velocity to move much faster. 3. Examine the image with a positive and a negative charge on the playing field with the positive puck. a. What do you think the arrows on the puck are illustrating?  Arrows represent the direction and magnitude of charges affecting the puck. Red is repelling and blue is attracting. b. How does the arrow from the positive charge compare and contrast to the one from the negative charge?  The positive arrow points away from itself. The blue points towards the negative charge. c. Which way do you think the puck will move? 12

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Physics Lab (Online Simulation)  The puck moves to the right. The arrows indicate the move to the right. It would travel the same magnitude because they both have the same magnitude. d. How would the arrows look if the puck was negative?  There would be an arrow pointing towards a positive charge. An arrow pointing away from the puck towards the left would indicate that there was a negative repel. 4. Open Charges and Fields . In this simulation, a little different model is used. The little yellow “E field sensors” are like the hockey puck but they are on a high friction surface, so they stay in place allowing for measurements. Collect data by turning on Values & drag in the Tape Measure like in this image: a. Investigate to check your answers from #2 and #3. Write how the results of your investigation support or change your ideas.  The simulation showed what I expected, where the positive and negative influences on the sensor showed what the influences were. b. Determine the relationship between distance and the strength of the electric field around a charged body. Turn on Grid and Values by clicking the box with a check mark. Uncheck Electric Field. Notice the scale is 0.5 meters for one big box. Place a positive charge at a point on the grid so that it crosses a big horizontal and big vertical line. Now drag the voltmeter to the charge, measure the potential at its center and record that value in Table 1. *Note: the voltmeter is very sensitive. You should get over 1000 volts at the center. Complete Data Table 1 by measuring the potential at each value indicated. Plot the electric field as a function of distance using Excel. Give the plot a title and axis labels. 13

Physics Lab (Online Simulation) Don’t forget units on the axis! Copy and paste the graph below Data Table 1. Adjust the size of graph so it fits nicely in the page. Question: Does your graph agree with the equation for an electric field? Why or why not? Yes, the distance is proportional to the electric field. The equation E =(9kQ)/r^2 proves this. Data Table 1 Potential at center of charge (V 1 ):  1061 V Distance (m) Potential (V 2 ) Potential Difference ΔV (V 2 -V 1 ) Electric Field -ΔV/D (V/m) 0.1 103 V -955 V 9572 0.2 48.04 V -1012.94 V 5064.7 0.3 30.21 V -1030.4 V 3435 0.4 23.53 V -1037.47 V 2593.6 0.5 18.6 V -1042.45 V 2084.81 1.0 9.062 V -1051.933 V 1051.943 1.5 6.065 V -1054.936 V 703.295 2.0 4.511 V -1056.483 V 528.246 2.5 3.623 V -1057.381 V 422.957 Insert Graph here: c. Determine the relationship between amount of charge and the strength of the electric field around a charged body. 14

Physics Lab (Online Simulation) Place a positive charge on the crosshairs of the grid as you did in part b. Measure the potential and record the value as V 1 for 1 +e charge in Data Table 2. Now measure the potential 1 meter from the test charge and record the value as V 2 . Complete Data Table 2 by measuring each value indicated. *Note: stack charges on top of each other aligning as best as possible. Plot the electric field as a function of charge number in Excel. Be sure to include a title, axis labels and units! Copy and paste your plot below the data table 2. Question: Does your graph agree with the equation for an electric field? Why or why not? Yes, the curve is a linear line where the electric field is directly correlated with the charge. Data Table 2 Charge (+e) 1 2 3 4 5 V 1 8.993 V 17.96 V 26.93 V 35.96 V 44.95 V V 2 8.165 V 16.35 V 24.41 V 32.63 V 40.76 V ΔV -0.8344 V -1.673 V -2.505 V -3.324 V -4.163 V E-Field= - ΔV/D 8.34 16.7 25.0 33.2 41.6 Insert Graph here: 5. Explain how electric fields are like gravitation fields and how they differ. The Electric field may be helpful. . Both electric and gravitational fields both have forces that act on other objects. The forces get weaker due to an inversed distance from the field and object. Both electrical and gravitational 15

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Physics Lab (Online Simulation) fields have a direction and magnitude. They differ where gravitational fields deal with masses and electrical fields deal with charges. Gravity deals with very large objects with mass while electric fields deal with small objects. 16

Electric Charge Field Online Jonathan

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