electrostatic+forces+2015

Electrostatic Forces

NOTE FOR NEXT YEAR: HANG TWO POP CANS NEAR EACH OTHER AND USE VAN DE GRAF TO CHARGE THEM (CONDUCTION WITH SECONDARY SPHERE) TO SHOW THEM REPEL Week 1







Week 2



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PRACTICE TEST

1) What is an electric field? What causes them? How could you detect one? 2) What what kinds of charges are attractice and which ones are repulsive. 3) What is the charge on an electron and on a proton? Are they the same +/- sign? 4) What is Coulumb's Law and what are the variables and units? 5) What is similar and different about the formula for gravitation and the formula for electric force? Why is this such an important idea? 6) What does Fe and Fg have to do with the "theory of everything?" (not the movie, the concept) 7) How does a Van de Graf generator work? 8) Explain all the phenomenon we experienced by playing with the Van de Graf 9) How does lightning form? What does lightning and static cling have in common? 10) What are the ways you can charge an object? 11) What does "grounding" have to do with shocking someone? How does "charge imbalance" play into giving/receiving a shock? 12) Why can atoms never touch? What does the concept of "mathematical limits" help explain this idea? 13) If atoms are made of up mostly empty space, why can we move through the walls? 14) How do you calculate electrostatic levitation if given the mass of an object? 15) If you were to calculate the initial force and direction of a charged metal sphere as a reaction to two different stationary charges, would the object continue in that direction with that force? If not, what kind of path would it travel?

Problems

1) Two metal spheres are 0.55 meters apart. One sphere has a -3 micro-Coulumb charge. The total force between the two spheres is +25 N. What is the charge on the other sphere and how many excess protons/electrons are on it?

2) Due to a sudden burst of electromagnetic radiation from the sun, a 1.5 cubic meter region in space holds 1700 trillion excess electrons. What is the volume charge density of this region in space?

3) A rectangular metal plate with dimensions of 0.35 meters by 0.45 meters has a surface charge density of -4.0 x 10^-1 C/m2. What is the total charge on the plate and how many excess electrons are present?

4) Two identical metal (0.25 meters on each side) plates are 0.15 meters apart. One plate has 1000 trillion excess electrons and the other has half as many. What is the total repulsive force between the plate? What is the surface charge density for each plate?

5) A 50 gram metal disk with a total charge of -1.48 x 10^-7 C is laying flat on a table. An identical disk with identical charge is placed above the first disk. How high in the air will the 2nd disk levitate?