DOC PREVIEW
PCC PHY 213 - Experiment: Coulomb’s Law & Electric Charge

This preview shows page 1-2 out of 5 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 5 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 5 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 5 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Experiment: Coulomb’s Law & Electric ChargeThe Experiment:The configuration:The physical model:Data collectionComplications:Final questionsPHY213: General Physics III page 1 of 5PCC-CascadeExperiment: Coulomb’s Law & Electric ChargeThis lab involves the study of the amount of surface charge on a piece of Scotch tape when one piece of tape is quickly pulled from another. Preliminary work: You can prepare a piece of charged tape by following the procedure described below. 1. Use a strip of tape about 20cm. Shorter pieces are not flexible enough, longer pieces are difficult to handle. Fold over one end of the strip to make a non-sticky handle: 2. Stick a strip of tape with the handle down onto a smooth flat surface (desk).3. Smooth this base tape down with your fingertips. This base tape provides a standard surface to work from. (Without this base tape, you get different effects ondifferent kinds of surfaces)4. Stick another tape with a handle down on top of the base tape5. Smooth the upper tape down well with your fingertips6. Write U (for Upper) on the handle of the upper tape7. With a very quick motion, pull the U tape up and off the base tape, leaving the base tape stuck to the desk. Following this procedure twice will enable you to produce two pieces of tape whose surface charge has the same sign (the tapes are both negatively charged but the sign of the charge is not significant for this experiment). Make sure that you repeat each step in the procedure.You should practice doing this so that you can quickly produce two pieces of similarly charged tape. You can test that the sign of the charge is the same by letting the tapes hang vertically from your fingers and bringing them toward each other. They should show a deflection as sketched below. handlePull RapidlyUpper tapeBase tapePHY213: General Physics III page 2 of 5PCC-CascadeThe Experiment:The configuration:Using two pieces of charged tape hang one from the edge of the table and hold another (tightly stretched) perpendicular to the hanging tape as shown below:As the stretched taped approaches the hanging tape you should see a deflection of the hanging tape. A side view of the deflected tape is shown below together with the forces acting on it. Charge q in this areaStretched tapePHY213: General Physics III page 3 of 5PCC-CascadeThe physical model:In this picture we have approximated the repulsive force between the tapes by a single force F directly opposite from the stretched piece of tape. We shall assume that this force is given by Coulomb's Law with the charge q given by amount of surface charge in the common square region where the two tapes cross each other (see the figure above). Since the tape strips are prepared using the same procedure we also assume q is the same for both tapes. Using these approximations the repulsive force F on the hanging tape is given by:2E2qF = ky� �� �� �rIf you hold the stretched tape steady the hanging tape will remain stationary. This means that the total torque of the tape by all external forces must be zero. Take the torque about the point P this implies that:net E W E WE E = + = 0 = -F z = - W x F z = W x t t t t t�� � � � �r r r r rr r r rr r r rYou can use the above two equations to obtain an equation for q in terms of measurable quantities. You should do this now and check with you partner (and other groups) that your equation is correct. Working Equation: (write it here)WrEFrzrxryrPHY213: General Physics III page 4 of 5PCC-CascadeData collectionOnce you have your final equation you should perform some experiments which will enable you to determine q. You will need to measure distances as accurately as possible so take some time to determine the best way to perform these measurements. Use at least two different sets of equilibrium distances to determine values for q. This will give you some confidence that the experiment is yielding consistent results.You will also need to know the mass of the hanging tape. There is full spool of tape and an empty spool that can be weighed for this purpose. Note: Calculate the length density of the tape then use this value and the length of your tape strip to determine the mass of the tape segment.Mass density of tape: ____________Table 1Trial mtapeWtapex y z qAverage:Complications:As you hold the tape there is a slow migration of charge from the tape to your hand, i.e., thetape discharges. Over a short period of time this is not a serious problem but if the measurements take too long then the charge q is not the same for different measurements. If you touch the tape in the middle, the tape will discharge in that region and q will be significantly reduced. There is then nothing you can do but cheerfully start over.Verification by Direct Measurement:1) Connect a charge sensor to the LabPro interface.2) Start the LoggerPro software.3) Attach the red and black leads to ground. Press the “Reset” button to zero the sensor.4) Connect the red lead to a metal can or bowl (placed in a larger glass bowl for insulation).5) Carefully insert one of the charged tape strips into the can (the tape should not touchthe can).6) Collect about 5 seconds of charge measurements. Using the “Statistics” tool, calculate the average and standard deviation values for the tape strip. easure the total charge of the tape. Record charge value in Table 2.7) Repeat step (5) with the second tape strip.PHY213: General Physics III page 5 of 5PCC-CascadeTable 2: Direct MeasurementMean Uncertaintyqstrip 1qstrip 2Average:Final questions1) What is the measured charge, q, in the square overlap area of the crossed pieces of tape(from Table 1)?2) From your answer in (1), determine the surface charge density () in this region.3) Calculate the total charge on hanging tape segment using your value from (2).4) From the measurements in Table 2, how do the total charge values compare between the2 pieces of tape?5) Compare the total charge calculated in (3) with the direct measurements (4). Calculate the % Error between these


View Full Document
Download Experiment: Coulomb’s Law & Electric Charge
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Experiment: Coulomb’s Law & Electric Charge and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Experiment: Coulomb’s Law & Electric Charge 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?