Capacitors Lab

.pdf

School

University of Texas, San Antonio *

*We aren’t endorsed by this school

Course

1631

Subject

Physics

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by AdmiralRhinoceros4442

1 Capacitors Lab Online Purpose The purpose of this activity is to examine how the applied voltage and the basic geometry of a two plate capacitor affects things such as how much charge the capacitor is holding, the amount of electrical energy stored in the capacitor, and the electric field between the two plates. Theory A simple two plate capacitor consists of two plates of the same area A, separated by a distance d. When one of these plates in connected to the positive side of a potential difference source Δ V, and the other plate is connected to the negative side of the potential difference source, then a charge Q builds up on each plate. A positive charge will build up on the plate connected to the positive side of the potential difference source, and a negative charge will build up on the plate connected to the negative side of the potential difference source. As shown in the diagram to the right. The ratio of the magnitude of charge that builds up either plate and the potential difference that is applied to the plates gives a term called the capacitance C of the capacitor. The SI units of capacitance are Farads, F. 𝐶 = 𝑄 ∆𝑉 As we already know electric charges generate electric fields, and the electric charges built the two plates of the capacitor are no different. Since the two charges are of the same magnitude Q, and separated by a constant distance d, a uniform electric field is generated between the two plates. Here we are ignoring what is called the fringe effects, meaning the electric field at the edges of the two plates and beyond. In the diagram to the right, we can see that the electric field points from the positively charged plate towards the negatively charged plate.

2 Since each plate has on it a charge of magnitude Q, and has a surface area of A we can write the following equation. 𝑄 = 𝜎𝐴 Where Q is the magnitude of the charge on either plate, A is the surface area of either plate, and σ (sigma) is the surface charge density on the plate, meaning charge per area. Also, since the electric field between the two plates is uniform, we can write the following equation for it. 𝛥𝑉 = 𝐸𝑑 Here Δ V is the electric potential difference between the two plates, which by conservation of energy is equal to the electric potential being applied to the capacitor. E is the electric field between the two plates, and finally d is the distance that separates the two plates. Lastly, it can be shown that the magnitude of an electric field between two oppositely charged plates can be given by; 𝐸 = 𝜎 𝜀 𝑜 Where E and σ represent the physical quantities previously stated, and 𝜀 𝑜 is the Permittivity of free space. 𝜀 𝑜 = 8.85 ∙ 10 −12 𝐶 2 𝑁𝑚 2 ⁄ When we insert these three equations into our equation for the capacitance and apply a bit of algebra, we end up with the following: 𝐶 = 𝜀 𝑜 𝐴 𝑑 Here we have an equation for the capacitance of a capacitor that is related to its geometry, and independent of the charge built up on it and the potential difference being applied to it. The purpose of a capacitor is to store some electrical energy for later use. A typical example of this is the flash bulb on a camera. When taking a picture with the flash on a small amount of electrical energy is stored in a capacitor that is connected to the flash bulb. When the button is pressed, the charge stored in the capacitor is released, and then quickly flows through the flash bulb causing it to flash.

3 Setup 1. Go to the following website: Capacitor Lab - Capacitor | Capacitance | Circuits - PhET Interactive Simulations (colorado.edu) 2. You should now see the following: 3. Click on the Play Button to download the Legacy Java Version, and then open the software when it has completed downloading. Additionally, you may be able to run the Browser-Compatible Version directly from the website. This does not work for some computers.

4 4. Once the simulator loads you should see the following: Procedure: Part 1 1. Near the top right of your screen select the following: a. Capacitance b. Plate charge c. Voltmeter 2. Use your mouse to move the positive probe (red) of the voltmeter so that it is touching the top plate of the capacitor, and then move the negative probe (black) so that it is touching the bottom plate of the capacitor. a. You may have to adjust the positions of the probes during the lab as you move the capacitors ’ plates. 3. Use the sliding scale on the battery so that the voltmeter reads about 1.500 V. a. Record your value in table 1. 4. Using the green arrows that are ‘attached’ to the capacitor plates near the center left of your screen to set the initial separation to 5.0 mm, and the initial area to 100 mm 2 . a. Record these values in Table 1, for run 1. b. Also, record the values for Capacitance, and Plate Charge. 5. Select 6 more combinations of separation, and areas, then record their values, and the values for Capacitance and plate charge that go with each. Procedure: Part 2 1. Near the top right of your screen make sure the following are selected: a. Capacitance b. Plate charge

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Recommended textbooks for you

Physics for Scientists and Engineers with Modern ...

Physics

ISBN:9781337553292

Author:Raymond A. Serway, John W. Jewett

Publisher:Cengage Learning

University Physics Volume 2

Physics

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Glencoe Physics: Principles and Problems, Student...

Physics

ISBN:9780078807213

Author:Paul W. Zitzewitz

Publisher:Glencoe/McGraw-Hill

College Physics

Physics

ISBN:9781938168000

Author:Paul Peter Urone, Roger Hinrichs

Publisher:OpenStax College

Physics for Scientists and Engineers, Technology ...

Physics

ISBN:9781305116399

Author:Raymond A. Serway, John W. Jewett

Publisher:Cengage Learning

College Physics

Physics

ISBN:9781305952300

Author:Raymond A. Serway, Chris Vuille

Publisher:Cengage Learning

SEE MORE TEXTBOOKS

Recommended textbooks for you

Physics for Scientists and Engineers with Modern ...
Physics
ISBN:9781337553292
Author:Raymond A. Serway, John W. Jewett
Publisher:Cengage Learning
University Physics Volume 2
Physics
ISBN:9781938168161
Author:OpenStax
Publisher:OpenStax
Glencoe Physics: Principles and Problems, Student...
Physics
ISBN:9780078807213
Author:Paul W. Zitzewitz
Publisher:Glencoe/McGraw-Hill
College Physics
Physics
ISBN:9781938168000
Author:Paul Peter Urone, Roger Hinrichs
Publisher:OpenStax College
Physics for Scientists and Engineers, Technology ...
Physics
ISBN:9781305116399
Author:Raymond A. Serway, John W. Jewett
Publisher:Cengage Learning
College Physics
Physics
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Cengage Learning