regents lab 2_1 edited s18

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The Bronx High School of Science Physical Science Department Dr. J. Donahue, Principal Dr. A. Wheeler, Assistant Principal Name _________________________________________ Partner(s) _______________________________________ Teacher _______________________________________ Day/Periods _________ Date _______________________ Experiment 2.1 (Regents): Static Electricity and Using an Electroscope Do Now: As a positively-charged rod is brought near a negatively-charged electroscope, the separation of the electroscope leaves will: (circle one) increase / decrease / stay the same Diagram: Explanation: _____________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Problem: How are charges gained and transferred? Hypothesis: See “Predicted Charge” column. Materials: Needle electroscope; vinyl and acetate strips; rubber and glass rods; wool, cotton, fur and silk cloths; 2 metal rods/bolts and Styrofoam cups; box/books. Given data: Item Procedure Item acquires Item Procedure Item acquires rubber rod rub with fur (-) charge glass rod rub with silk (+) charge vinyl (brown) strip rub with wool (-) charge acetate (clear) strip rub with cotton (+) charge Procedure (make your predictions in the data table first): 1. Touch the knob of the electroscope with your finger to ground it. The electroscope needle should now be vertical (red end points to the bottom). If it still shows any deflection, have another group member try. 2. Rub the rubber rod with the fur for at least ten seconds to build up a reasonable charge. As per the given data, the rod should now be negatively charged. 3. Briefly touch the rubber rod to the knob of the electroscope. The needle should deflect approximately 45 degrees. If it does not move, repeat step 2 and try again. If only a small deflection is observed (e.g. on a humid day), you may try running the rod across the knob several times to "scrape" the charge off the rod and deposit it on the electroscope. If it is a very dry day, and too much deflection is observed, ground the electroscope again, and try charging the rod less and repeating the procedure. Roughly 45º is the optimal deflection of the needle. IMPORTANT : From this point on, nothing should touch the electroscope knob. When nothing is near it, you should continue to observe the 45 degree deflection. If this is ever not the case, you must repeat steps 1-3. 4. Now, try the first investigation. Rub the vinyl strip (not the clear one) with the wool for several seconds. Bring the vinyl strip near the electroscope (do not touch it!). You should observe the deflection of the needle increase while vinyl is nearby, and return to 45 degrees when it is moved away. This indicates that the vinyl is the same charge as the electroscope (negative). Record this result in your data table. 5. Next, try the same procedure, but this time bring the wool near the electroscope instead of the vinyl (do not touch it!). You should observe the deflection of the needle decrease while the wool is nearby, then return to 45 degrees when it is moved away. This indicates that the wool has the opposite charge of the electroscope (positive). Record this result in your data table. 6. Follow the procedures in your data table to test the remaining items. Regularly re-test with the rubber rod to make sure the electroscope retains a negative charge. If there is any reason for doubt, you must repeat steps 1-3. Summary Questions: Each Q MUST include diagram(s) and an explanation based on your knowledge of static electricity (and the behavior of electrons). 1. A neutral electroscope (red pointer straight down) will deflect in the presence of a positively charged object, just as it will in the presence of a negatively charged object. Explain. 2. Explain the results of experiment number 5. 3. Explain the results of experiment number 7. 4. Explain the results of experiment number 9.
Data Table Directions: For the predicted charge column: use the four referenced pair of materials above, your knowledge of static electricity, and the properties of conductors and insulators to predict the polarity of the excess charge. For the actual charge column: use the negatively charged electroscope to verify your predictions. # Procedure Item Predicted Charge Actual Charge 1 Rub vinyl (not clear) strip with wool vinyl wool 2 Rub acetate (clear) strip with cotton acetate cotton 3 Place a rod on a styrofoam cup, then touch rod with charged vinyl. metal rod 4 Repeat #3 with acetate instead of vinyl. metal rod 5 Setup as shown; bring charged vinyl ~ ½ inch from left end of rod. right end of rod 6 Repeat #5 with acetate instead of vinyl. right end of rod 7 (a) Hold charged vinyl ½ inch from left metal rod while both rods are touching, then separate the two rods while holding the vinyl in place. (b/c) Then, test each rod individually. left rod right rod 8 Repeat #7 with acetate instead of vinyl. left rod right rod 9 (a) While holding charged vinyl ½ inch from rod, touch rod briefly with finger. Take finger away, then take vinyl away. (b) Test the rod. metal rod 10 Repeat #9 with acetate instead of vinyl. metal rod
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