PHYS320 Lab 27 Electric Fields
Experiment 1: Static Materials
1. What happens when you bring the charged strip near the paper pieces? Why does this happen?
2. What happened when you brought two vinyl strips near each other? Draw a rough diagram depicting the direction of electric field lines between the two surfaces.
3. What happened when you brought the charged aluminum near the charged vinyl? Draw another diagram noting the direction of the electric field lines between these two surfaces.
4. Do you know which of these materials picks up positive charge and which picks up negative charge? How might it be possible to determine this?
5. What happened when you brought the charged rod near the metal surface? Explain what is happening in terms of free electrons.
Experiment 2: Static Balloons
1. What types of objects did the balloon stick to best? What can you conclude about the way charges in these objects react to the balloon’s charge?
2. Explain why the balloons either attracted or repelled each other in step 5. What happens when you put your hand in between them?
3. Your hand is a neutral object. Why does this happen if your hand does not carry any net charge (Hint: think about charge by induction)?
Experiment 3: Simple Electroscope
1. What happens to the strips of aluminum when you bring a charged object near them?
2.What can you say about the charge in the strips—are they like or unlike? How do you know
3.Is your charged electrode like or unlike the charged rod? Why?
4.Does it matter which charge—positive or negative—is on the object you are testing?
5.Is this an example of charge by induction or conduction?
Lab 4: Pith Ball Electroscope
1. What happened when you brought the charged vinyl near the electroscope?
2. What did you notice when you brought the aluminum strip near the pith ball that was charged by the vinyl?
Use Coulomb’s law to explain why the electroscope does not seem to be affected by the charged material at a distance of about 10 cm, but reacts significantly at a distance of 3 cm (distances are approximate).
4. How could you design an experiment to measure the Coulomb force between the charged material and the electroscope by measuring the angular acceleration of the electroscope? Assume you have measured the radius of the rotating electroscope, R, and the distance between the charged material and the pith ball, r.
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