Coulomb's Law 2023

Page 1 of 8 PHYS 2021 Electric Field Vectors Lab 27 January 2023

Physics 2021 Electric Field Vectors Lab 27 Jan 23 Page 2 of 8 In this lab you will learn how to calculate the electric field due to multiple field charges. For a field created by two point charges you will calculate the magnitude and direction of the electric field vectors at test charges placed in the field. The magnitude and direction of the electric field vectors are given on the simulation graphic. You will calculate the net electric field vector on three test charges and compare them to electric field vectors on the screen. The qualitative magnitude of the electric field vectors for the entire field is given by the relative brightness of the vectors. You will notice that the field vectors more distant from the field charges are lighter in color than those closer to the charges. The magnitude of the field vectors at a test charge is proportional to the length of the vector. The magnitude and direction of the field vector at a test charge are given at the tail of the vector. Procedure 1. In your web browser go to http://phet.colorado.edu . a. Click on Simulations . b. On the Simulations drop-down menu click Physics. c. Uncheck every topic except Electricity, Magnets & Circuits . d. Click on the Charges and fields icon . e. Click on the arrow to run the simulation. 2. Running the Simulation a. Check the Grid and the Values boxes. b. Check the Electric Field box to show the electric field vectors. c. Use a lighter background. Click the Phet icon on the bottom right of the screen and choose options ; check the projector mode box and close then window. d. The placement of the field charges and the test charges is crude. If you use the full screen your charge placement will be more accurate. When calculating the distance between charges you may use the measuring tape on the simulation or the Pythagorean Theorem by counting the x and y distances between the charges. Using the Pythagorean theorem is easier. 3. Configuration 1 a. Place one positive field charge and one test charge (sensor) on the grid as in Figure 1 . The sensor has a charge of 1 coulomb. i. The length scale is defined at the bottom right of the grid. ii. Place one field charge at the intersection of two major grid lines. iii. Place a positive test charge 1 meters to the right of the field charge and 0.5

Physics 2021 Electric Field Vectors Lab 27 Jan 23 Page 4 of 8 4. Configuration 2 a. Create a dipole by placing a negative field charge in the previous field as in Figure 2 . Figure 2 b. Calculate the magnitude and direction of the electric field at the location of the test charge q 1 . c. To calculate the electric field at a test charge due to more than one field charge, the electric field vector on the test charge due to each field charge must be calculated separately; and then the two electric field vectors must be added vectorially. i. The electric field due to the positive test charge was already calculated in configuration 1. ii. Use the same procedure to calculate the electric field due to the negative field charge. iii. The magnitude of the net electric field at q 1 due to both field charges is calculated from the vector equation sign on the components of . . Remember to use the correct iv. The angle of the electric field is d. Show your calculations using the equation editor.

Physics 2021 Electric Field Vectors Lab 27 Jan 23 Page 5 of 8

Physics 2021 Electric Field Vectors Lab 27 Jan 23 Page 7 of 8 Table 2 Electric Field vectors for Figure 3 Test charge position Electric field magnitude [ V/m] Net Electric field angle [degrees] E 1,x E 1,y E 1,net E 2,x E 2,y E 2,net E 3,x E 3,y E 3,net 6. Calculations a. The electric field at any is defined to be the electric force per unit charge. (8) b. is the Coulomb force of the field charge Q on the test charge q . The force has units of newtons. c. (10) . i. k is the Coulomb force constant: . ii. Q is the magnitude of the field charge with units of coulombs. iii. q is the magnitude the test of charge with units of coulombs . iv. r is the distance S in units of meters S between the field charge and the test charge. v. is a unit vector along an axis extending through the two particles. The direction of is determined by the polarity of the charges. d. The angle of the electric field vector is calculated using the inverse tangent function.

Physics 2021 Electric Field Vectors Lab 27 Jan 23 Page 8 of 8 7. Report a. For your report show your calculations on this document where they are required and complete the tables. Everything must be typed. b. The equations defining the calculations will be included using the equation editor in the word processor software. c. Show that the units N/C and V/m are equivalent.