Coulomb's Law

Coulomb’s Law Peter Ciezczak September 12, 2014 1 Introduction In 1785, Augustin de Coulomb experimented on charged objects and examined their attractive and repulsive forces. Coulomb determined that the magnitude of the force exerted from one charge to another charge is equal to the charges multiplied by the k constant divided by the distance squared. This is now called Coulomb’s Law and is expressed as: (1) where F is the force that the charge exerts onto the other charge, k is the constant of proportionality or Coulomb’s constant, R is the distance between the objects and q1 and q2 are the values for the charges on each object. Like charges repel while opposite charges attract. 2 Experimental Methods Materials: The Material that was used during the experiment consisted of a pith ball electroscope, mirror scale, rabbit fur, acrylic rod, nylon, wool, cat’s fur, silk, rayon, plastic, rubber, PVC, and Teflon. Procedure: Part 1 1) Prepare the lab station by setting up the pith ball electroscope with the glass scale underneath with the materials in order. 2) Choose three rods and two materials to be used for Part 1. 3) Charge the rod by rubbing the rod with each material and touch the top of the pith ball electroscope. 4) Observe the distance between the pith balls and record the data. 5) Repeat steps 3 and 4 until all the material and rods are used. Part 2 1) Keep the same setup as in Part 1, but silk will be used as the material along with all 6 rods.

2) Knowing that silk rubbed with acrylic is positive, determine the charge produced when rubbed with a different rod. 3) Observe the charge, and record the data. 4) Repeat steps 2 and 3 until all the charges are known. Part 3 1) Keep the same setup as in Part 1, and determine what the unknown material is. 2) Rub the unknown material with any rod and determine if it is rabbit or cats fur. 3) Record the data. Data Part 2

Acrylic Nylon Rayon Plastic PVC Rubber

Part 1 Silk postive no result no result negative negative negative

(in cm) Silk

Wool

Rubber Acrylic Rayon 1 3.2 1.2 1.1 2.6 1.4 0.9 3 1.3 0.8 1.5 1.3 1 1.1 1.7 0.9 1.7 1.9

Figure 1 and 2: The tables above is the data collected after performing parts 1 and 2 of the experiment. Error To reduce error during each part, avoid touch the electroscope with anything but the rod when necessary. As a person touches it while it is charged, it will lose all the charge that is stored in it. The major source of error is measuring the distance between the two pith balls. Therefore, to reduce error, try to take the measurement when the pith balls are parallel with the glass scale. To make it easier when recording the distance, have one pith ball start at zero. These are the sources of error that may arise when performing this experiment. However, this may affect my results as the charges are really small. So the littlest error can change the actual value when calculating. 3 Results and Discussion For part on of the lab, silk and wool was chosen as the material while rubber, acrylic, and rayon was chosen as the rods. After observing the figure which states the magnitude of charge each material and rod has in the manual, the results seem to be correct. Silk with rubber and rayon

have low distances as they are closer to the neutral zone while acrylic has a higher distance. The reason is that it carries over a much greater charge. For wool, each of the rods have results that would make sense as wool is in the positive area. The distance between wool and each rod in the figure is not that far apart. Therefore, the distance on the electroscope should not be that far apart either which is what happened. For part two, the data collected seems to be correct. Since silk is neutral, it just depends on the rod used. According to the figure presented in the manual, the rod’s charge follows it. However, for nylon and rayon, a charge was not presented as the pith balls would not move due to the low charge. For part three, it was concluded to be rabbit fur since the distance between the pith balls was much greater compared to the results used in part one. The data collected is strong as all the number are close together except for wool and rayon. The data collected was scattered. However, for part two, the data collected was accurate as it matched the figure. The data supports the argument as equation one follows through what was done. 4 Conclusion Coulomb’s law is equal coulomb constant multiplied by each charge divided by the distance squared. This law holds true as the pith ball electroscope experiment support the ideas of the forces, attraction, and repulsion. In order to make this experiment better for myself, I wish I could take better measurements as I took my time so it lost its charge. In part one remember that since like charges repel, you are able to measure a distance between the two pith balls. In part two remember that you like repel and opposites attract. So you can use that to determine the charge that the rods produce. In part 3, use what you learned in part 1 and 2 to make your conclusion the mystery fur. 1.

(

)

2. Charge

Silk Wool

# of eRubber Acrylic Rayon 4.6154E2.3335E6.8524E10 09 10 2763732256 1.3973E+10 4103248331 3.9482E10 7.94E-10 9.669E-10 2364220391 4754471233 5789819055

3. The gravitational attraction is really small compared to the attraction/repulsion force due to the electrostatic force. The reason is that the pith balls weight .00004 kg each so it has no effect compared to the electrostatic force.

Gravitation attraction Rubber Acrylic Rayon Silk 1.07E-15 1.2403E-16 6.3148E-16 Wool 1.32E-15 5.1946E-16 4.0003E-16

4. The mystery fur was rabbit fur confirmed by trying multiple rods to test the strength of the charge. The test to determine if it was cat’s or rabbit fur was to determine the distance between the two pith balls. From previous lectures, it is known that rabbit’s fur is more positive than cat’s fur. So by comparing the distances, a person can determine if it is rabbit or cat fur.