PH 221 Grantham University Week 1 Coulomb Law Lab Report

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PH 221

Grantham University

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PH221 – Week 1 Lab

Coulomb’s Law

Before you can start working on the labs you must set up an account at KET Education and download the labs to your computer. Please follow these directions to access your physics labs.

Welcome to the Lab component of Physics II. All our labs use simulation applications of real laboratory equipment that are combined with measurement and graphing tools to allow you to explore, observe and analyze experiments. Each week you will complete one laboratory exercise using a virtual lab application and then use your results to write a formal lab report. Each experiment will be based around one main topic.

For this week’s lab you will use the Electrostatics simulation. Download and read the following user guide to familiarize yourself with the simulation.

Download the instructions for two laboratory activities you will complete this week. You may wish to print them out and use to collect and organize your results.

Coulombs Law Lab

Use the data and answers to the laboratory questions to help you write your lab report. Your lab report should focus on calculating the coulomb force acting on the charged pith balls and the charge on each pith ball. Then you should compare those experimental results with the actual charge indicated in the simulation.

The lab report will have the following six sections. Include section headings in bold at the beginning of each section.

Introduction – Explain the purpose of this laboratory and what results you expect to see in this experiment.

1.Background – Discuss the concepts that form the foundation for this lab. You should address what you learned from the weekly lectures and readings that are related to the lab.

2.Methodology – Describe the apparatus that was used in the experiment(s) and how it was used in performing the experiments. Also explain what tools were available within the laboratory that allowed you to collect or analyze the data.

3.Data – Enter the data that you collected in the lab. You can use screen shots from the Data Table within the Pivot Interactives labs. Data should be clearly labeled with physical quantities and units.

4.Analysis – Analyze your results. If your Data Table included Calculated Columns, then the equation you used in those calculations should be included and described here. Any graphs created with the data go in this section, as well as your interpretations of their meaning. Were your results consistent with your original expectations?

5.Conclusion – Provide a concise summary of the results of your experiment(s) – what you did, what you found and what it means. Speculate on possible sources of experimental error and/or uncertainty within the experiment. Describe an additional experiment that could be run with this equipment to expand on what you’ve learned OR explain how you could use this equipment to answer another real-world problem.

PH221: Rubric for Laboratory Assignment 4

OVERRIDE GRADE OF 1:

If a PDF file is used, name and GID must be on each page.

All of most of the screenshots are missing.

Screenshots lack a time stamp (when indicated)

Lab worksheet file(s) not submitted along with the lab report.

The following screenshots required with a computer timestamp included:

“Faraday_Bmin_max.png"

“Faraday_5_points.png.”

“Faraday_Emf_steps.png.”

Lab Report

Use the answers to the laboratory questions to help you write your lab report. Your report will focus on measuring the emf induced in a coil of wire when the magnetic field varies. You should discuss the factors that influence the magnitude of this emf.

Introduction

10

The purpose of the lab is clearly stated and is aligned with the lab objectives. Expected results are proposed.

8

The purpose of the lab and expected results are stated and consistent with the assignment.

6

The purpose of the lab and expected results are stated but lacks clarity or is not consistent with the assignment.

2

The stated purpose is not aligned with the lab objectives or missing key elements.

0

The introduction is missing.

Background

10

The concepts that form the foundation of the lab are discussed. Reference to the weekly lectures or readings are made.

8

Concepts that underly the lab are discussed, but no reference is made to the weekly lectures or readings.

6

Concepts that relate to the lab are discussed but are vague or contain minor errors.

2

Underlying concepts are described but reveal major errors in understanding.

0

The background was not addressed

Methodology

-Include a screenshot of the Faraday apparatus and description of how it works.

10

Methods, materials and equipment are specifically described using proper terminology. Concise, but detailed, procedure is provided.

8

Methods, materials and equipment are described, and a detailed procedure provided, but minor errors in terminology or descriptions are made.

6

Materials, methods and equipment are described, and a procedure provided, but they are too brief or vague to easily follow.

2

Some materials, methods and procedures are described, but they are not coherent or missing major pieces.

0

The methodology was not provided.

Data

Include:

- Screenshots corresponding to “Faraday_Bmin_max.png"

“Faraday_5_points.png.”

“Faraday_Emf_steps.png.”

-Completed Table 1 – Magnetic Field at 5 Positions

20

Adequate data is collected in the lab is presented in a logical way that is organized and clear. Data is relevant to the purpose of the lab. Tables and observations are complete, clearly labeled, and physical quantities and units are given when appropriate.

15

Adequate data is provided and relevant to the purpose of the lab, but with minor errors in labeling or units. Tables and observations are complete and generally include captions and units.

10

Relevant data is provided, but it is not adequate to address the purpose of the lab or contain errors or omissions so that it is difficult to derive useful information from the data.

5

Data provided is not relevant to the purpose of the lab. Data is not organized or major errors in labeling and units appear throughout.

0

Little to no organization of the data was present. Lacks data.

Analysis

Include:

- Completed Table 2 – Emf measured by Pickup Coil

- Discussion of the factors that influenced the magnitude of the induced emf.

20

Data is analyzed appropriately, and key results are presented in a logical sequence. All required calculations are included. Sample calculation(s) are provided to show how the calculations were done. All variables include units when appropriate.

15

Data is analyzed, but with some details missing. All required calculations are included but with minor errors.

10

Data is analyzed, but with key details missing or inaccurate. One of the required calculations is missing or major mistakes made in the calculations.

5

Data analysis is included but does not include the required calculations or major errors in the calculations are made.

0

Date analysis is lacking.

Conclusion

30

Conclusion contains a concise summary of the results, speculates on the possible sources of error and uncertainty in the lab, and proposes an experimental extension of the lab or applies its concepts to a real-world situation.

20

Conclusion is provided, but only two of three elements are well addressed.

10

Conclusion is provided but only summarizes the results.

5

A conclusion is provided, but does not communicate useful information about the results, sources of error or possible laboratory extensions.

0

A conclusion was not provided

Unformatted Attachment Preview

KET Virtual Physics Labs KET © 2019 Name School Date Coulomb’s Law Purpose To observe the effect of the electrostatic force on light-weight charged objects. To experimentally determine the charge on a sphere small sphere acting as the bob of a pendulum. Equipment Virtual Electrostatics Lab PENCIL Explore the Apparatus/Theory Open the Virtual Electrostatics Lab on the website. Figure 1 In this lab you’ll observe a typical large-scale manifestation of the forces between electrically charged objects. We’ll pit the force of gravity against the electrostatic force to determine the amount of charge on each of a pair of small identical spheres – pith balls. The operation of the Virtual Electrostatics Lab is very simple. A certain amount of charge is acquired by a charging rod when this rod is rubbed against the charging cat which has volunteered to take part in this experiment. Part of this excess charge is passed on to two initially neutral conducting pith balls which then share it equally. The pith balls are immediately forced apart by the Coulomb repulsion between them. They swing back and forth, gradually slowed by air resistance, until they are in static equilibrium as shown in Figure 1. If there was just one ball present its excess charge should be a spherically symmetrical surface charge. Because they are similarly charged – both negative – conductors placed near one another their excess charge would actually be skewed outward away from one another. To minimize the effect of this the balls have been made very small. The balls will be considered small enough relative to their separation VPL Lab – Coulomb’s Law 1 Rev 12/19/18 KET Virtual Physics Labs KET © 2019 distance that the redistribution of charge on them is insignificant. We’ll assume that the charge on each ball takes on a spherical distribution. So why does that matter? 𝐹=𝑘 $% $& '& Coulomb’s Law In Coulomb’s Law, r is the distance between the charges, q1, and q2. But our pith balls have charges spread all over their surfaces. So the force is actually the sum of all the forces between all the individual charges – electrons and protons – and each pair has a different r. Fortunately, if the (excess) charge is distributed evenly on a spherical surface, the force is the same as if the charge was all located at the center of each sphere. So r is just the distance between the centers of the pith balls. We now want to find to find the charge on one of the pith balls. Since they’re equally charged – they have an equal number of excess electrons – we’ll just call the charge on either ball, q. Your goal is to find q, (in Coulombs.) So how’s that going to happen? Let’s try out the apparatus first to get a clearer idea of what’s going to happen. Figure 2 shows how the apparatus looks at start up. Refer to Figure 1 for terminology. The parallel plates that are omitted from the figure are not used in this lab. 1. Notice that the charge number and charge on each ball in the info box both read zero. The charge number is a reference number that you’ll record for grading purposes. It’s meaningless otherwise. The charge on each ball is initially zero since they are initially uncharged. (Take a screenshot for the methodology section of the lab report). 2. Click anywhere on the charging rod. Keeping an eye on the info box, drag the rod so that the ball on its end moves across the cat. The more you drag it across the cat the more the charge # increases. The ball is fully charged when the number reaches 120. Try it. 3. Drag the charging rod until the charging ball touches the tip of the grounding rod. Poof. Back to zero. You can also move the grounding rod to touch the charging ball to discharge it. 4. Recharge the rod to a charge # > 50. Now drag it until it its ball touches either of the pith balls. Some charge has now been transferred. The pith balls equally share it. 5. You’re going to need to know the deflection angle, θ, between either ball and the vertical. That’s what the protractor is for. Move your pointer over the protractor Figure 2 until the pointer changes to a hand (or whatever). Click and drag it up near where the strings are tied and release. It should snap in place. (Take a screenshot for the lab report). Hold down the space bar until the curved edge of the protractor almost reaches the pith balls. You should now be able to read the angle between either string and the vertical line at 0°. This deflection angle is the angle you’ll be using in your calculations. You can shrink the protractor back down with the key and drag it out of the way when you don’t need it. VPL Lab – Coulomb’s Law 2 Rev 12/19/18 KET Virtual Physics Labs KET © 2019 Note: You can right-click or -click (Mac) to zoom in at any time. But while zoomed in you can’t drag anything. 6. To measure the separation between the centers of the balls, click on the ruler, somewhere to the left of 35 cm, and drag it to a convenient place beneath the pith balls. You’ll want to measure the distance between their centers when taking data. (Take a screenshot for your lab report) 7. You may also want to measure the length of the pendulum – the distance from the tie-off point to the center of a pith ball. Clicking to the right of 35 cm and dragging up or down will rotate the ruler. You can then align it with the string. Finding the charge, q on a pith ball Apparently the angle, θ, between the strings is important and we haven’t discussed why, so let’s have a look at that. Figure 3 (3a) (3b) In figure 3 you see two pairs of pith balls hanging from strings. Beside each ball is a dot where you’ll draw force vectors to create a free body diagram, FBD. In each FBD the balls will be in equilibrium. This means that ++++⃑* = 0 and ΣF ++++⃑. = 0 ΣF In figure 3a the pith balls are side-by-side and the strings are vertical. (This is impossible with this apparatus since the strings are attached at a point, but that won’t be an issue since we aren’t concerned with their behavior at this angle.) The vertical orientation of the strings could indicate one of two things. The balls could be oppositely charged. But we’ll never see that case since our pith balls can only be neutral or negatively charged. 1. What then can you say about the charges on the pith balls in Figure 3a? 2. Each pith ball is hanging at rest. What are the two (external) forces acting on, say, the left ball in Figure 3a? Strong nuclear, weak nuclear, friction, gravity (its weight), electrostatic, tension, air resistance 3. How do the magnitudes and directions of these two forces compare? (They are not accelerating.) The forces are 4. (Circle two) and . Draw a FBD for the right-hand ball in Figure 3a using the dot provided. Use the same scale as the FBD on the left ball. USE A PENCIL. In figure 3b the balls have been equally charged. Both are hanging at the same angle, θ either side of the vertical line. 5. Keeping the same scale, add a weight vector to the right ball’s FBD. (Ignore the weight of the excess electrons.) 6. The ball is in equilibrium, so there still must be an equal upward force. In figure 3a that force was the tension force. But the tension is no longer acting in the upward direction. It’s now acting in a direction of θ degrees relative to the vertical. The upward force is the y-component of the tension, Ty. Draw this vector and label it Ty. Be careful with your scale. VPL Lab – Coulomb’s Law 3 Rev 12/19/18 KET Virtual Physics Labs KET © 2019 7. You now have T’s y-component. From it you can draw the actual tension vector, T. Carefully add it to the FBD. 8. Explain how you knew how long the vector T should be. 9. Add the angle θ to your FBD. 10. You now have T and Ty on your FBD. Clearly there is a horizontal component of T, Tx. Add that to your figure. Draw it with its tail starting at the dot. Again, be careful with your scaling. We now have W, T, Ty, and Tx in our FBD. Are all these forces acting on the pith ball? Not exactly. We have some redundancy. T is the vector sum of Tx and Ty. So T has actually been replaced by its components. 11. Draw a “≈” through the T vector to indicate that we can ignore it now. 12. Look at our remaining three vectors. Does our FBD indicate that the ball is in equilibrium? 13. What type of force, missing from our FBD, is keeping the ball in equilibrium? Strong nuclear, weak nuclear, friction, gravity (its weight), electrostatic, tension, air resistance (Circle one) 14. Add that force vector to your FBD and label it Fe. Draw it with its tail starting at the dot. Again, be careful with your scale. 15. Draw the matching FBD for the left ball. Your sole task is to determine the charge on either pith ball and compare it to the value given in the info box. Here are some guidelines and suggestions. • Charge up the pith balls to start. Use a large charge for best results. • The forces involved are gravity (weight), W, the string tension, T, and the Coulomb force, Fe. Forces that are not horizontal or vertical will need to be resolved into correctly-labeled components. • Record any data you take in the data table provided. You may add to the table. • Explain your method in words, referring to labeled figures. (You supply the figures.) (Item 1 below.) For clarity’s sake, refer to the right-hand ball in your discussion. • Clearly show your calculations using the proper variable terminology. (Item 2 below.) Define any variables that you create. E.g., Fe: electrostatic force between pith balls Wait as long as possible before replacing your variables with numbers. (See Ex.) Ex. a = 2.5 m/s2, Vo = 12 m/s, Vf = 22 m/s, t =? Wrong 5 2.5𝑚/𝑠 = Right 556⁄79:56⁄7 ; VPL Lab – Coulomb’s Law 𝑎= , etc. 4 => 9=? ; , 𝑡= => 9=? A , 𝑡= 556⁄7 9:56⁄7 5.B6/7 & = 4.0 s Rev 12/19/18 KET Virtual Physics Labs KET © 2019 Table 1 Charge on a Pith Ball (you may not actually need all of these values) k = 9.0×109 N m2/C2 mass of a pith ball (from lab info box), m = _____________ kg charge # = _____ accepted value for charge on one pith ball (info box), Qa = _____________ C experimental value for charge on one pith ball, Qe = _____________ C separation between centers of pith balls, r = _____________ m length of the pendulum, L = _____________ m deflection angle of a pith ball from the vertical, θ = _____________ ° 1. Explain your method in words, referring to labeled figures. (You supply the figures.) VPL Lab – Coulomb’s Law 5 Rev 12/19/18 KET Virtual Physics Labs KET © 2019 2. Clearly show your calculations using the proper variable terminology. Include the calculation of percentage error for your value of the charge on a pith ball. 3. What do you feel was the major source of error? Why? 4. Is the assumption that the charge distribution is spherical most inaccurate for small or large r’s? Explain. VPL Lab – Coulomb’s Law 6 Rev 12/19/18 KET Virtual Physics Labs VPL Lab – Coulomb’s Law KET © 2019 7 Rev 12/19/18
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Explanation & Answer

Here is the final report. I have also attached the completed worksheet.There are three files attached. The "Coulomb's_Law_Report" file is the final draft of the report. The "Coulomb's_Law_PDF" file is a PDF file of the completed worksheet. The "Coulomb's_Law_Worksheet" file is a MS Word document that has the written answers for the worksheet. I typed out the answers just in case there was any confusion with the written answers in the PDF file. The answers in the word document go in the order on the worksheet, and they have the same assigned numbers as in the worksheet.Please let me know if you have any questions or concerns, or need a different format for the final report.

Name
Date
Coulomb’s Law Lab
Introduction
This laboratory experiment explores the effects of Coulomb’s law on two identical, spherical pith
balls. A simulated lab is used in order to find the theoretical charge on each pith ball. The
measurements taken from the simulated lab were then used to calculate the objective of this lab;
the charge on each pith ball. The Coulomb force acting on the pith balls, as well as the charge on
each pith ball, are analyzed and compared for both the theoretical and experimental procedures.
Because of the principles behind Coulomb’s law, it is expected that both the experimental and
theoretical values will be greatly similar.

Background
Coulomb’s law describes the electrostatic force between two charged particles. When two
charges, 𝑞1 and 𝑞2 , are separated by a distance 𝑟, Coulomb’s law can describe the electrostatic
force between them as follows:
𝑘𝑞1 𝑞2
𝐹=
𝑟2
1
where 𝑘 is Coulomb’s constant. This electrostatic force decreases by the ratio of 𝑟 2, which is also
known as the inverse square law. In an experiment, this inverse square law relationship can be
1
observed when the distance increases because the magnitude of the force will decrease by the 𝑟 2
ratio.
This electrostatic force, Coulomb’s force, is what causes the two charged particles to repel one
another. If the two pith balls have the same charge but opposite sign, they will repel and separate
by some distance 𝑟.
C...


Anonymous
Very useful material for studying!

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