ANS Lab 02_Charge_Force_Field_v1

Lab 02: Charges, Electric Force and Electric Field You will need to run a simulation to do the lab. Answer the following questions as you work through the lab . Write your answers in blue . Re-load the file in Word or PDF format in Moodle before the due date. Lab Objective: 1. Learn how electric charges interact with an external electric field. 2. Understand the vector nature of electric force between charges and an external electric field. Material: Stop watch (e.g. you can use your smartphone for this). Introduction: The electric force acting on a charge q in an external electric field E is given by the relation 𝑭 !" =𝑞𝑬 . The stronger the external field, the larger the electric force. Also, a large charge can experience a large force in a weak electric field. In this lab, you will simulate the force acting on a charged particle in an external electric field. This lab is mostly qualitative. Simulation: Open the Electric Field of Dreams simulation in the PhET.colorado.edu website. https://phet.colorado.edu/en/simulation/efield Take a few minutes to become familiar with the simulation. Click all the buttons, check the “properties” of your charge. Change the values of mass and charge. Change the size and direction of the “external electric field” by dragging the blue dot (see figure below). For the simulations below, set the length of the electric field vector to about 1cm (see figure below), unless stated otherwise. 1a. Force on a positive charge: Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/ Change this

i. Click on the Properties button. Set the charge to 0.10 and the mass to 10. Click on the Add button. You should see a blue charge moving under the influence of the external electric field. Pause the motion of the charge and drag it to the middle of the box. “Play” the simulation again. Q1: Which direction does the charge move? a . Along the direction of 𝑬 b. Opposite of the direction of 𝑬 a. right b. left Q2 : What is the direction of electric force 𝑭 ? a . Along the direction of 𝑬 b. Opposite of the direction of 𝑬 a. right b. ii. Set the direction of the electric field so that it points to the right . Q3: What direction does the charge move? right iii. Set the electric field, 𝑬 in different direction and fill out the table below. Try to keep the magnitude of 𝑬 constant. Keep the mass at 10. Start the charge at a location that will allow for maximum travel. All observations should be made on the motion before the first bounce on the wall. Charge Direction of 𝑬 Direction of motion Direction of 𝑭 Describe the motion 0.1 Right Right Moves to the right in uniform motion 0.1 up Up Moves up in uniform motion 0.1 Left Left Moves to the left in uniform motion 0.1 Down Down Moves to the down in uniform motion 1.0 Right right Moves to quickly to the right due to increase in charge magnitude Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/

-0.1 Right Right Moves slowly in the oppositedirection of the e-@ield and electric force -0.1 Up Up Moves slowly in the oppositedirection of the e-@ield and electric force -1.0 Left Left Increases speed moving right in the oppositedirection of the e@ield and electric force -5.0 Left Left Increases speed moving right in the oppositedirection of the e@ield and electric force -10.0 Left Left Increases speed moving right in the oppositedirection of the e@ield and electric force -20.0 Left Left Increases speed moving right in the oppositedirection of the e@ield and electric force 2. Electric force as a function of the magnitude of the electric field, 𝑬 . For this part of the lab, you will keep the magnitude of the charge fixed and change the magnitude of 𝑬 2a. Force on a positive charge: Set the size of the charge to 0.5 and keep the mass at 10. i. Set the magnitude (the arrow) of 𝑬 to very small (almost zero). Label this as E 0 . Describe the motion of the charge in the space below. Do the same for four different magnitudes of 𝑬 . Describe the motion for each of the cases. Make sure you write the relative size of the electric field you use (e.g. E 1 = 2 E 0 , E 2 = 4 E 0 …etc.). This doesn’t have to be exact. 1. E 0 : has trouble moving along the direction of the small force vectors and e-field due to the decreased e-field 2. E 1 : slowly moves along the direction of the force vectors and e-field with slightly more speed 3. E 2 : moves along the direction force vectors and e-field with a slightly more uniform motion Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/

4. E 3 : quickly moves with the direction of the force vectors and e-field in a smooth motion 5. E 4 : moves the fastest along the direction of the force vectors and e-field 2b. Force on a negative charge: Set the size of the charge to -0.5 and keep the mass at 10. i. Set the magnitude (the arrow) of 𝑬 to very small (almost zero). Label this as E 0 . Describe the motion of the charge in the space below. Do the same for four different magnitudes of 𝑬 . Describe the motion for each of the cases. Make sure you write the relative size of the electric field (e.g. E 1 = 2 E 0 , E 2 = 4 E 0 …etc) 1. E 0 : moves in a slow stuttered motion in the opposite direction of the force vectors and e-5ield. 2. E 1 : moves at average pace with a smoother motion in the 3. E 2 : moves at a moderate pace with a smooth motion in the opposite direction of the force vectors and e-5ield. 4. E 3 : moves quickly in the opposite direction of the force vectors and e-5ield. 5. E 4 : fastest and smoothest movement in the opposite direction of the force vectors and e-5ield. Summary of electric force on a charge in an external electric field: Force on a charge in an external electric field 𝑬 is given by 𝑭 𝒆𝒍 =𝑞𝑬 . Answer the following questions. 1. If the charge is positive it will move in the same / opposite direction of the electric field. Same direction 2. If the charge is negative it will move in the same / opposite direction of the electric field. Opposite direction 3. A 2.0mC charge in an external field of 20N/C , North will experience a force of: 40*10^-3 Newtons, the direction of the force North 2*10^-3 x 20N/C = 40*10^3 Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/

pace going in the same direct E-Field and Force Vectors 6. q=0.1, m=0.2 1.30 Moves very quickly along the direction of the E- Field and Force Vectors 7. q=0.2, m=10 6.26 Moves at a moderate speed along the direction of the E-Field and Force Vectors 8. q=0.4, m=20 6.58 Slowly moves along the direction of the E- Field and Force Vectors Summary of part 3: Answer the following questions: Q7. What relation can you state about the acceleration of the charge and it mass? Describe the mathematical relation, such as “ directly proportional “ , or “ inversely proportional ” …etc. Newtons 2 nd Law of Motion can be combined with the equation from question 1 (F = qE) to give us the following equation (a = qE/m). This states that the acceleration of a particle is inversely proportional to its mass while directionally proportionally to the charge and electric 5ield. Q8. What relation did you see in trials 7 and 8? Does it match with the mathematical relation between the acceleration, mass and the charge given in Eq. 1.2? Yes, when comparing trials 7 and 8, the latter moved slower because the increasein charge was not large enough to counteract the increasein mass, thus it had less acceleration than trial 7. Had the increasein the mass and charge been proportional in both trials then the acceleration would have remained constant. Q9. An electron ( 𝑚=9.11×10 !!" 𝐾𝑔 and charge 𝑞=−1.60×10 !!" 𝐶 ) is inside a parallel plate capacitor as shown in the figure. The electric field (shown with red arrow) has a magnitude of 2000N/C. The electron is initially at rest. Answer the following questions. i. What is the force on the electron (magnitude and direction)? Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/

F = qE F = (-1.60*10^-19 x 2000 N/C) F = -3.20*10^-16 N ii. What is the acceleration of the electron? a = F/m a = (-3.20*10^-16 N / 9.11×10^-31 kg) a = 3.51*10^11 m/s^2 Q10. Replace the electron in above question with a proton ( 𝑚=1.67×10 !!" 𝐾𝑔 and charge 𝑞= +1.60×10 !!" 𝐶 ). i. What is the force on the proton? F = qE F = (1.60*10^-19 x 2000 N/C) F = +3.20*10^-16 N ii. What is the acceleration of the proton? a = F/m a = (+3.20*10^-16 N / 9.11×10^-31 kg) a = 1.92*10^11 m/s^2 Simula’on created by the Physics Educa’on Technology Project (PhET) c/o The University of Colorado at Boulder hAp://phet.colorado.edu/