Electrostatics lab Introduction: Static electrical charges are either positive or negative. Similar charges repel each other, opposite charges attract. Electricity can be discharged by grounding a charged object. Materials: Balloons Meter stick String Van de Graf generator Safety: Give each group enough space to operate. Shoes should be worn at all times. Procedure: Part A. Opposite and similar charges 1. Inflate and tie off two balloons of similar size and shape. Tie a 30 cm (approximately) thread to each balloon. 2. Rub each balloon on your head or pants to cause a negative electrical charge on the balloons. 3. Loosely tie each balloon at opposite ends of the meter stick. Suspend the meter stick and balloons between two chairs. 4. Move the balloons closer to each other but don’t let them touch. Record what happens on your own paper. 5. Bring your hand between the two balloons. Record what happens. 6. Move the two balloons so they touch each other. Record what happens. Part B. Positive and negative charges 1. Touch the balloons to discharge the static electricity. They should hang straight down. 2. Shred some paper into small pieces (but remember you will have to pick up all the pieces of paper before you leave class). 3. Charge one of the balloons by rubbing it on your hair or pants. Drop the paper on top of the balloon. Describe (record) what happens. 4. Charge the second balloon and bring it up close to the balloon with the confetti. Describe what happens. 5. Without brushing the paper off, see if you can get it to fall off by itself. Part C. Producing a large charge 1. Observe the interaction of the Van de Graf generator and the ping pong ball. 2. How long a spark can you get? (try different materials) 3. What if you are touching the generator and someone else? Or the sink? 4. With the generator OFF, tape a thumb tack to the generator. Turn it on. Hold your hand about an inch away from the point of the thumbtack. What do you feel? Why? 5. Experiment with the materials that are available at this station. See what happens with the Styrofoam balls, the rice crispies, the fluorescent light, string, bits of paper, and what ever else you can think of. Describe what happens in each of your experiments. 6. The voltage of the generator can be found by measuring the size of the globe, and realizing that it takes about 3 million volts to discharge across a distance of 1 meter of air. Measure and record the size of the globe and approximate the longest electric arc you can draw off the globe. You will use these measurements to calculate the voltage in #13 below. Data/Results The data will consist of all your observations and calculations written on your own paper. Make sure you number each observation according to the procedure. (i.e. C4. etc.) Conclusion: Answer the following questions on your own paper. You may need to refer to your book, chapter 32 and 33. 1. What charge does the balloon in Part A have? This means it has an excess of _______________. 2. WHY do the two balloons act the way they do when they approach each other? 3. What happened as the balloons got closer to each other? 4. Use Coulomb’s Law to explain this: If the distance between the balloons doubles, what happens to the amount of force attracting the balloons? 5. How could you calculate the charge on the balloons if the force and distance was known? Physics students: if the distance is 10 cm, and the repulsive force is 9.0 x 10-7 Newtons, what is the charge on the balloons? (see p. 634-636) 6. What kind of charge does your hand have? How do you know? 7. What kind of charge did the pieces of paper have? 8. WHY did the paper stick to the balloon? 9. How did you get the paper to fall off the balloon after it was sticking to it? 10. Why did the ping pong ball bounce back and forth from the generator (Part C)? What two forces were acting on it? 11. Draw a picture of the generator (find the diagram in your book) showing the charges that were on the generator and ball. 12. After a number of electric discharges, a strange (but pleasant) odor can be detected in the vicinity of the generator. It can also be smelled during or just after a thunderstorm, and if you have an electrostatic air cleaner in your home, you can detect it there as well. What is this odor? (there is a name for it – research it). 13. How many volts (approximately) can our Van de Graf generator generate? Show your calculations according to this formula: Voltage of generator = 3 million volts x radius of globe x distance of electric arc. Make sure your distance units are all in meters. 14. Write a conclusion about what you did and what you learned in this lab.
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