1 Static Electricity Lab part 2

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Dec 6, 2023

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1 Summer 2022 Static Electricity STATIC ELECTRICITY BACKGROUND The word electricity comes from the Greek word electron which means amber (a tree resin that has been fossilized). When rubbed, a piece of amber can attract small objects like tiny pieces of paper. Later, other materials were found which exhibited this same behavior. Today we know that the source of this attraction is due to the presence of static electric charge. Electric charge comes in two forms: positive and negative. Electrons carry negative charge and protons carry positive charge. Most materials are electrically neutral – they have an equal number of positive and negative charges (thus an equal number of protons and electrons). Static electricity occurs whenever you have an accumulation of one type of charge. This can happen when two non- conducting materials are rubbed together – for example plastic and fur. A static charge is produced because some electrons are transferred from one object to the other. The material losing electrons now has fewer electrons than normal and becomes positive. The material gaining electrons now has more electrons and becomes negative. Surrounding a charge there is an invisible electric field which gets weaker the farther away one gets from the charge. Electric field lines are typically drawn to visualize the field. For a positive charge, the field is directed outward from the charge (figure 1a). For a negative charge, the field is directed inward towards the charge (figure 1b). As a result, like charges repel each other and unlike charges attract each other. a b Figure 1. illustrates the direction of the field in a positive and negative charge. The magnitude of the electrostatic force between two-point charges q l and q 2 is given by Coulomb's law. where r is the distance between the two charges and k is called the proportionality constant and is equal to 9 x 10 9 N.m 2 /C 2 . The direction of this force is determined by the sign of the charges: like charges repel and unlike charges attract and acts along the line between the two point charges. If a neutral material is placed inside a weak electric field, it will not experience a net force, because it contains an equal number of positive and negative charges. However, if a neutral object is placed inside a strong electric field, the material may become polarized . Inside a polarized material, positive and negative charges are no longer randomly distributed and are slightly separated 2 2 1 r q q k F =

2 Summer 2022 Static Electricity (positive on one side, negative on the other). Figure 2. Distribution of charges in a polarized and non-polarized object Using Coulomb’s law, we can explore the effect of the distance, between two charged particles, on the force between them. This force decreases as the distance between the charges increases. The electric field surrounding a charged object gets weaker with distance, the object will have a stronger attractive force on its closest charges of opposite sign and a weaker repulsive force on the like charges farther away. Thus, the polarized material will experience a net attractive force. For example, if you charge a balloon by rubbing it on your hair, it can stick to a neutral wall. In a metal, a charge can move freely and stay on the surface. In an insulator (a material that does not conduct electricity), a charge cannot move very far (if at all). Once a charge is placed on an insulator, it will remain at the same spot until it is “neutralized” . Coulomb’s Law: https://phet.colorado.edu/sims/html/coulombs-law/latest/coulombs-law_en.html Charge laboratory: https://phet.colorado.edu/sims/html/balloons-and-static-electricity/latest/balloons-and-static- electricity_en.html

3 Summer 2022 Static Electricity Name(s): Aries Naranjo, Priscilla Coronado LAB REPORT: STATIC ELECTRICITY Part 1 Learning Goals: Students will be able to describe and draw models for common static electricity concepts. (transfer of charge, induction, attraction, repulsion, and grounding) Part 1a: Test your understanding: Without using the simulations, predict the answers to these questions, then use the simulation below to check your ideas. Question 1: When the balloon is rubbed on the sweater, what might happen? Which of the options below do you predict for the answer? [ B ] Open the simulation to verify your prediction above: https://phet.colorado.edu/sims/html/balloons-and-static- electricity/latest/balloons-and-static-electricity_en.html ,

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4 Summer 2022 Static Electricity Question 2: From the simulation, what happens when the balloon is rubbed on the sweater? When the balloon is rubbed on the sweater the balloon gained the negative charges (electrons) from the sweater and the sweater stayed with the positive charges. Since they have different (unlike) signs for their charges they attract each other. Explore the simulation to develop your own ideas about electrical charge. Then, describe some of your experiments and your observation with captured images from the simulation. [Paste captured images below and include description/explanation of what is going on in the image] When exploring the simulation, the sweater lost its negative charges (electrons) and only the positive charges stayed making it overall positive. The balloon gained all the negative charges (electrons) from the sweater and became negatively charged and the sweater lost its negative charges (electrons) to the balloon and became positively charged. Since the positively charged sweater and the negatively charged balloon have different signs for their respective charges, they attract each other and that is why they stick together.

5 Summer 2022 Static Electricity Question 3: What do you think will happen when the balloon is moved closer to the wall? Which of the options in the second picture below would you predict for the answer? [ A ]

6 Summer 2022 Static Electricity Verify your predictions using the simulation. So, what did you observe? [Paste captured images below to support your answer] By using the simulation, I was able to prove my answer/prediction was correct. What I was able to observe was that when the negatively charged balloon was near the neutral wall the balloon polarized the charges in the neutral wall. The negative charges from the neutral wall moved away from the negatively charged balloon and the positive charges from the neutral wall came closer the negatively charged balloon. That is why neutral wall and negatively charged balloon attract each other.

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7 Summer 2022 Static Electricity Question 4: Consider the situation below with two negatively charged balloons. What do you think the balloons will do? Which of the options in the second picture below would you predict for the answer? [ B ]

8 Summer 2022 Static Electricity Verify your answer in Question 4 and write down below your observation. [ Paste captured images below to support your answer] By using the simulation, I was able to verify my answer/prediction was correct. In the simulation both negatively charged balloons moved away from each other due to the electrostatic force. The direction of the force depends on the charge’s signs so two similar sign charged particles will repel each other and why two different (unlike) sign charges attract each other.

9 Summer 2022 Static Electricity Part 1b: Open John Travoltage at https://phet.colorado.edu/en/simulation/john-travoltage then explore to develop your own ideas about electrical charge. Question 5: What might happen to the charge on the man when he touches the doorknob? Encircle your prediction. [ A ] Verify your prediction and write your observation(s) below: By using the simulation, I was able to verify my answer/prediction was correct. In the simulation, when John Travoltage’s foot is rubbed against the ground, the negative charges (electrons) get directed up into his leg and the rest of his body. When his hand is pointed towards the metal knob, the negative charges (electrons) in his body then move into the metal knob and back into the ground.

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10 Summer 2022 Static Electricity

11 Summer 2022 Static Electricity Part 2 In this part you will study the concept of electric field. Open https://phet.colorado.edu/sims/html/charges-and-fields/latest/charges-and-fields_en.html Use the settings shown in the figure (Turn ON Values only). Drag one negative charge, the E field sensor, and Tape Measure into the simulation screen. a. Determine the relationship between distance and the strength of the electric field around a charged body. Get about eight pairs of electric field (E) and distance (r) measurements. To measure the distance (r), position the Tape Measure in such a way the one of the crosshairs (+) is on the middle of the sensor and opposite crosshair is placed at the middle of the charge. Please see figure below. Use an Excel Worksheet to document your data, graph, and determine the equation for the relationship. Copy and paste your data table and graph from your spreadsheet below. Measuring the distance (r)

12 Summer 2022 Static Electricity b. Determine the relationship between amount of charge and the strength of the electric field around a charged body. You can stack charges on top of one another to make the amount of charge vary. Decide on the distance that you want to use. Get at least six different pairs of measurements for the charge and the electric field. Use an Excel worksheet to document your data, graph, and determine the equation for the relationship. Insert your data table and graph from your spreadsheet.

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13 Summer 2022 Static Electricity Question 6. Based on your results in parts a and b above, how does the electric field depend on the distance from the charge and the amount of charge? Once you have completed the assignment, save your report as a PDF and upload using the blackboard submission on the lab course page (found under “Lab Online Submissions”)

1 Static Electricity Lab part 2

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