Lab 1 : Electrostatics and Triboelectric Series

Seneca Polytechnic
SES250 Electromagnatics

Purposes

  • To demonstrate that there are two types of electric charges in nature
  • To be familiar with scientific experimental techniques
  • Use experimental observation and apply logical reasoning to build a triboelectric series

Objectives

  • Perform qualitative observation of the following:
    • the separation of electric charges by friction
    • the existence of two types of charges
    • the existence of electrostatic forces between charged objects

Description

Objects are usually electrically neutral. The number of positive charges and negative charges is usually equal. Neutral objects neither attract nor repel each other electrically. This balance of charge can be upset by rubbing an object against another object further explained in Chapter 5.1 of University Physics Vol 2 or by the presence of another nearby charged object further explained in Chapter 5.2.

In this lab, the attractive and/or repulsive electrostatic force between charged objects will be observed using a setup shown in Figure 1.1. You will confirm the presence of electric charges and the forces exerted by these charges.

Figure 1.1 Lab 1 Setup

Figure 1.1 Lab 1 Setup

Triboelectric Series

"The triboelectric series ranks various materials according to their tendency to gain or lose electrons, which reflects the natural physical property of materials. Static electricity occurs when there is an excess of positive or negative charges on an object’s surface by rubbing certain materials together. The position of the material in the triboelectric series determines how effectively the charges will be exchanged. Normally, the build-up of static electricity would be undesirable because it can result in product failure or a serious safety hazard11,12 caused by electrostatic discharge and/or electrostatic attraction. This series can be used to select materials that will minimize static charging to prevent the electrostatic discharge or electrostatic attraction."

Source: Quantifying the triboelectric series by Zou et. al.

Materials

  • A stand
  • String or fishing line
  • Paper clip
  • Plastic Straw (Polypropylene)
  • Plastic Wrap
  • Wool Cloth
  • Glass Rod
  • Steel Rod
  • Wooden Rod / Dowel
  • Silk Cloth or Cotton Cloth
  • Plastic Rod (Acrylic)

Preparation

Answer all the lab preparation questions at the end of this document in your lab notebook BEFORE your lab session. Students who did not complete the lab preparation will be asked not to join the lab and receive a grade of ZERO (0) for the lab.

Lab preparation must be done individually in the lab notebook.

Lab Preparation Question

  1. Summarize the steps for this Lab in your notebook as the computer in the lab room will NOT be available for this lab.
  2. Describe how you can neutralize your hand from electric charges in the lab room using the technique mentioned in the lab manual.

  3. Copy and fill in the following observation table in your notebook (except for the observation column):

    Step Object 1 Rubbed with Object 2 Rubbed with Observation (Attract/Repel)
    6 Plastic Straw Wool Plastic Straw Wool
    8 Plastic Straw Wool
    9 Plastic Straw
    12
    13

Procedures

  1. If not enough stands are available, work in groups of 2. All questions in the lab must be answered individually and every member must individually demostrate completion of the lab.
  2. Place and secure the stand on the table. Attach a paper clip onto a strong then hang the paper clip about 5cm below the end hook of the stand. The paper clip is used to hold a plastic straw.

  3. Carefully secure a plastic straw onto the paper clip so it evenly sits on the paper clip and it's free to rotate on the stand.

    NOTE: In some instant, it might be beneficial to hang the stand off the side of the table to allow full rotation of the straw once it's attached to the paper clip.

  4. Technique and attention to detail is the key to this lab and in any of your future lab. Remove the plastic straw from the paper clip then rub both ends of a plastic straw with the wool cloth. ONLY handle the middle of the straw as handling the ends you've charged will alter its charge.

  5. Once charged, carefully suspend the plastic straw from the stand using the paper clip. ONLY handle the middle of the straw. What you've done is charging the plastic straw NEGATIVELY (free electron from the wool cloth is transferred onto the surface of the plastic straw).

    Note: If your hand touched the charged portion of the straw, your hand will discharge the straw causing the charged portion to return to neutral.

  6. Next, rub one end of a second plastic straw in the same way then hold it close to the first plastic straw (without touching). Remember, do not hold the straw on the side that you've charged. Observe the (attractive or repulsive) force exerted on the first plastic straw suspended from the stand.

    Lab Question 1: What interaction between the straws do you observe? Write it down into the observation table you created in the pre-lab.

    Lab Question 2: Which electrostatics law have you confirmed? Explain your answer by specifying the charge in each plastic straw.

  7. Ensure your hand is not charged by placing your palm on the metal surface or the rubber mat on the workbench. Then discharge the second plastic straw by slowly touching it (not rubbing) with your hand then neutralize your hand. Repeat this a few times until the second straw no longer exerts any force on the first straw.

    Note: Technique is critical. You should often discharge yourself by placing your palm on the metal surface or the rubber mat of the workbench. We can assume they are connected to the ground (earth) and are electrically neutral.

  8. Recharge the second (now neutral) plastic straw by rubbing it with the plastic wrap. Hold it close to the first wool-charged plastic straw and observe the nature of the force.

    Lab Question 3: What interaction between the straws do you observe? Write it down into the observation table you created in the pre-lab.

    Lab Question 4: Use your observation to predict what type of charge is on plastic wrap-rubbed straw (positive or negative). ie. Did the plastic wrap-rubbed straw gain/lose electrons?

    Remember: It was previously given that the wool-rubbed straw is charged negatively.

  9. Discharge the second plastic straw. Take a glass rod and charge it using the wool cloth. Hold it close to the first wool-charged plastic straw.

    WARNING! The glass rod is fragile! Handle with care!

    Lab Question 5: What interaction between the straw and the rod do you observe? Write it down into the observation table you created in the pre-lab. Use your observation to predict what type of charge is on the wool-rubbed glass rod (positive or negative). ie. Did the wool-rubbed glass rod gain/lose electrons?

  10. Discharge the glass rod.

    WARNING! The glass rod is fragile! Handle with care!

    Lab Question 6: From the results in your observation table, which materials (plastic straw, wool, plastic wrap, glass rod) do you think will most likely gain electrons and which will most likely lose electrons?

    For example: We defined the straw as negatively charged when rubbed with wool. Therefore, the straw is more likely to gain electrons than the wool.

    The steps above demonstrate the triboelectric effects and electrostatic force between two charged objects. In the next steps, you will observe the force between a charged object and a neutral object.

  11. Touch a metal surface on the workbench to ensure your hand is not charged. Discharge the plastic straw on the stand and a glass rod with your hand until there is no electrostatic force between them when holding them near one another.

  12. Leaving the plastic straw neutral, charge the glass rob with the wool cloth. Hold the glass rod close to the plastic straw.

    Lab Question 7: What interaction between the rod and the straw do you observe? Write it down into the observation table you created in the pre-lab. Why is the neutral plastic straw attracted to the glass rob? Explain the phenomenon and discuss how this can draw you to the wrong conclusion regarding the charge on each object. Refer to Chapter 5.2 in the University Physic Volume 2 textbook if required.

    The steps above demonstrate transferring of charges on the surface of insulators. In the next step, you will observe what will happen when charging a conducting object.

  13. Leaving the neutral plastic straw suspended. Rub one end of a steel rod with the wool cloth then hold it near the neutral plastic straw.

    Lab Question 8: What interaction between the rod and the straw do you observe? Write it down into the observation table you created in the pre-lab. Explain the phenomenon. Refer to Chapter 5.2 in the University Physic Volume 2 textbook if required.

Once you've completed all the above steps, ask the lab professor or instructor over and demostrate you've completed the lab and written down all your observation. You might be asked to explain some of the concepts you've learned in this lab.

Bonus

  1. Using the concept you've acquired from this steps above, extend your observation table and determine where is the Plastic Rod or Slik or Cotton or Wooden Rod / Dowel is on the triboelectric series in Question 6. (5% of Lab Work mark for each materials). You must show your expiremental steps and observation.

Read the following cases to understand the logic:

Case 1: Plastic Wrap

If Material-A is rubbed with Plastic Wrap, Material-A is positively charged (lose electrons) because the Plastic Wrap is more negative (gain electrons).

Case 2:

If Material-A rubbed with Material-B is attracted to Material-C rubbed with Material-B, then we know the charge on Material-A is opposite to the charge on Material-C. However, to determine which one is positively charged and which on is negatively charged, we must know the properties of Material-B relative to Material-A and Material-C. As a result, always start your experiment with the known material (Plastic Wrap).

Once you've completed all the above steps, ask the lab professor or instructor over and demostrate that you've completed the lab and written down all your observations. You might be asked to explain some of the concepts you've learned in this lab.