Lab #1 Electrostatistics

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Dec 6, 2023

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Olivia Grigas, Stephanie Layland, Ashley Torres Physics 118 & 222 Lab 1 Electrostatics Introduction: Electricity is an important part of our lives, but it is easy to take it for granted and not think about what really happens when we get shocked by closing a car door or turning on a light switch. The purpose of this lab is to learn about static electricity by studying how an object can gain and lose excess electrical charge. Higher in the table = more likely to become positively charged by losing electrons. Human Hand Asbestos Rabbit Fur Glass Mica Human Hair Nylon Wool Fur Lead Silk Aluminum Paper Cotton Steel Wood Amber Hard Rubber, Nickel, Copper Brass, Silver Gold, Platinum Polyester Styrene (Styrofoam) Saran Polyurethane Polyethylene Polypropylene Vinyl (PVC) Teflon Lower in the table = more likely to become negatively

Olivia Grigas, Stephanie Layland, Ashley Torres charged by gaining electrons. Some of the basic ideas in electrostatics are the following: 1) Like charges repel, opposite charges attract. The more charge involved the stronger the force will be. The larger the distance between the charges, the weaker the force will be. (Coulomb’s Law) 2) It is only the excess charges that are important. 3) Charge is neither created nor destroyed. (Conservation of charge) 4) Charges are free to move through a conductor, but not through an insulator. (Occasionally an insulator can become a conductor. This is what occurs when a spark jumps between a gap and when lightning strikes.) 5) Electrostatic forces add as vectors. (Superposition) 6) Rubbing two different materials together yields opposite charges on each material. (This is often referred to as “charging by friction,” but that is somewhat of a misnomer. It is typically the pulling apart of the two objects that achieve the charge separation. When two objects slide past one another, they are in some sense being pulled apart continuously.) The list above gives a rough indication of which material will end up with the positive charge and which material will end up with the negative charge as a result of the rubbing. A material that is higher on the list (picture the list as one long column) gives electrons to objects lower on the list when they are rubbed together. (e.g.: Rub together glass and wool and the glass becomes positively charged.) Results may vary because of surface contamination and the amount of moisture in the air.

Olivia Grigas, Stephanie Layland, Ashley Torres Procedures: The following steps are designed to show how charges are gained and lost via friction, contact and induction. Use the effects in the introduction to explain each mini-experiment below. You should include diagrams that show where the excess charge is for each step. If you can’t tell whether the excess charge is positive or negative based on the chart, pick charges that are consistent with your experiment. You should test whether your explanations are correct by modifying the procedures when possible. Introduction: For this experiment, we will be conducting experiments to demonstrate the Four Big Ideas of Electrostatics. We will be demonstrating how charges are gained or lost due to contact and induction. The Four Big Ideas that we will be focusing on in this experiment are: Triboelectric Charge Separation, Polarization, Charge by Contact, and Charge by Induction. Experiments: 1) Scotch Tape a) Pull two 10 cm strips of scotch tape off a roll. Fold over one end of each strip so that they don't stick to your fingers. Now stick both of these to the table and pull them quickly off. Dangle the strips and try to bring them together. Describe what you observe and explain what happened to produce what you observed. Remember to draw a diagram showing the excess charge. Answer: When you rip the two pieces of tape off the table, there is a tug-of-war for electric charges between tape and the table. The tape either steals negative charges (electrons) from the table or leaves some of its own negative charges behind, depending on what the table is made of (a positive charge doesn’t move in this situation). In any case, both pieces of tape end up with the same kind of charge, either positive or negative. Since like charges repel, the pieces of tape repel each other. The process that took place in this was called triboelectric charge separation. b) Next, pass the entire length of each of the hanging strips lightly between two fingers several times, then hold the two strips near each other again. What happened? Explain. Be aware that you can get different results here depending upon how aggressively the tape is pulled through someone’s fingers. Discuss the results of this part with your lab instructor.

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Olivia Grigas, Stephanie Layland, Ashley Torres Answer: The tape became neutral after rubbing them with our fingers for our hands took the charge from them. Therefore, when they were put up against each other again, nothing happened. They neither attracted or retracted. c) Now carefully stick the two strips together so the sticky side of one strip adheres to the "dry" side of the other. You should end up with a double-thick layer of tape, which is sticky on one side and has two tabs at one end. Grasp those tabs and rapidly pull the strips apart. Hold them distantly separated, and then slowly bring them together. What happens? Explain what effects were involved. (Hint: If you want to show that friction is not involved, make sure you avoid rubbing the tape.) Answer: When the tape sandwich is pulled apart, one-piece rips negative charges from the other. One piece of tape therefore has extra negative charges. The other piece, which has lost some negative charge, now has an overall positive charge. This is because opposite charges attract, the two pieces of tape attract each other. Drawing: 2) The Balloon and the Wall Rub a balloon on your head and stick it to the wall. Explain how the balloon can stick to the wall even though the wall is not charged . Answer:

Olivia Grigas, Stephanie Layland, Ashley Torres Static Electricity is a familiar electric phenomenon in which charged particles are transferred from one body to another. When you rub your hair against a balloon, charge transfer occurs, and Static Electricity is produced. If you rub a balloon against your hair, the balloon will steal electrons from the hair, which leaves the hair positively charged and the balloon negatively charged. The balloon will most likely be attracted back to the hair because opposite charges attract. The reason that the balloon will stick to the wall is because the negative charges in the balloon will make the electrons in the wall move to the other side of their atoms (like charges repel) and this leaves the surface of the wall positively charged. This is because opposite charges attract, the negatively charged balloon will be attracted to the positively charged surface of the wall. Drawing: 3) The Dripping Faucet Charge a rubber rod by rubbing it with fur. Go to the back sink, turn it on slightly and place the rod near the dripping water. Describe this effect and explain why you see this. Answer: When the rubber rod is rubbed with fur, the electrons are transferred from the rod, giving the rod a negative charge. Two negatively charged objects repel eachother. When a positively charged object is brought near a negatively charged object the two objects attract one another. Therefore, when the rubber rod is given a negative charge by rubbing it with fur, the water is attracted to the rod causing it to bend toward the rod. Drawing:

Olivia Grigas, Stephanie Layland, Ashley Torres 4) The Electroscope An electroscope consists of two very light, conducting pieces of foil that are attached to a metal conducting post. This design is very similar to what was used for some of the original electrostatic experiments. Drawing: a) Charge the electroscope by conduction. To do this, rub the black rubber rod with a piece of fur. Now rub the rod on the top of the electroscope. The angle between the two leaves should increase. Which concepts are needed to explain this? (If the leaves touch each other, carefully lift the glass and slide your finger between the leaves to discharge them. If it still doesn’t work, check with your lab instructor.)

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Olivia Grigas, Stephanie Layland, Ashley Torres Answer: The concept that explains this is charge by contact. Charge by contact involves the contact of a charged object to a neutral object. In this process, the charged object was the black rubber rod. Then, the rubber rod touched the top of the electroscope, which is the neutral object. The charge from the rubber rod moved onto the neutral object causing the two leaves to increase. Due to the repelling of the neutral object to the charged object, the neutral object then formed a charge. This process is known as charge by contact. b) Discharge the electroscope by touching the metal top with your finger. This process is called “grounding” an object. Explain how grounding works . Can you discharge the electroscope if you touch it with an insulator rather than a conductor like your finger? Again, rub the black rubber rod with a piece of fur. This time, bring it near to, but not touching, the top of the electroscope. If you see a spark move from the rod to the terminal, discharge the electroscope and start over. Why do the leaves rise up? Compare and contrast this with part (4a). Answer: Grounding is the process of removing the excess charge on an object by the means of the transfer of electrons between it and another object. When a charged object is grounded, the excess charge is balanced by the transfer of electrons between the charged object and the ground. You can discharge the electroscope when you touch it because your finger is positively charged and the electroscope is negatively charged. The leaves rise up because it is repelled by the positive charge caused by rubbing the fur and the rubber rod. c) Repeat parts (4a) and (b), by using something from the chart above that gives the opposite charge as the rubber rod and the fur. Does the electroscope work the same for positive and negative charges? (This may be a hard one to get to work, because the rabbit fur and rubber combination is much better than other combinations of materials.) Answer: The materials we used for this was a silk tie and a glass rod. It was hard to see a difference because of the material we used. However, when we touched the glass rod to the electroscope, the two leaves repelled away from each other. When we only brought the glass rod close to the electroscope, the two leaves also repelled away from each other, however not as much as the first time.

Olivia Grigas, Stephanie Layland, Ashley Torres d) Charge the electroscope by induction. To do this, charge the black rubber rod with a piece of fur and bring it near to, but not touching, the top of the electroscope as you did in part b. While holding the rubber rod there, touch the top of the electroscope on the side opposite of the rod. Remove your finger and then remove the rod. Why do the leaves rise up when the process is finished? Compare and contrast this with part (4a). Answer: The difference from part A to part D was that the leaves did not move back down once the rod was removed. When the rod was removed after we touched the top of the electroscope, the leaves stayed up and did not fall back down. e) Discharge the electroscope. Charge the electroscope so it has a negative charge. What do you need to do to get a negative charge? Now bring a charged rubber rod close to, but not touching, the top of the electroscope. What do the leaves do? Why do they do this? Does this verify the negative charge of the rubber rod? Choosing two objects (not objects you have used previously in this experiment), try to charge each object, then one at a time, bring the object close to, but not touching, the top of the electroscope. For each object, what do the leaves do? Explain what charge each object has and why the motion of the leaves tells you what this charge is? Answer: In order to get a negative charge, in this experiment, you have to ground the electroscope with your finger. This will allow extra electrons to move to the electroscope and then it will become negatively charged. By bringing the charged rubber rod close to, but not touching the electroscope, this process is called charged by induction. The leaves separate and this is because the freely-moving negative charges in the electroscope are repelled by the charges in the rubber rod. This then causes them to flood the two conducting leaves of the electroscope with extra negative charge.However with the glass rod they did not move as far apart but still showed movement. The charged glass rod attracted the electrons to the top and left a net positive charge on the leaves. Conclusion: In these experiments, we were able to see the effects of what happens to certain objects when their charges are gained or lost. Through the four big ideas of electrostatics, we saw the difference between how the different types of procedures worked for each experiment. We applied our knowledge of how different charges either attract or repel each other and we saw the effects of each. In each of the experiments, we were able to see how everyday objects were used to demonstrate the ideas of electrostatics.

Lab #1 Electrostatistics

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