Need Pointers for Basic EM Theory (questions)
Hey all,
Just started taking EM last week and our first homework assignment gave me a bit of trouble...
1.) The first problem I had issues with utilized a setup of three spheres suspended from a common point by threads of length 1.17m. The mass of each ball is 13.3 grams and the spheres hang in the shape of an equilateral triangle of side length 15.3 cm. (Find charge of each ball if they are identical.)
I tried using Coulomb's law with two of the spheres where the force is equal to 0 as the balls aren't moving, but I'm not sure that this is the correct way to go about solving this problem (seems too easy...) I got 6.88 x 10^8 C for the charge on each ball.
Anyone know if this is the correct way to solve this problem?
2.) The second problem was even a bit harder fro me to reason out. It involves a setup of 4 rods of length 25.0 cm with a uniform (1d) charge distribution. They form the base of a pyramid, the top of which is a small sphere of mass 3.46 x 10^4 grams and has a charge of +2.45 x 10^12 C. If it is in equilibrium 21.4 cm above the center of the square formed by the rods, what is the charge on each rod?
I wasn't sure how to do this one at all. The professor showed us an example of the (1d) uniform charge distribution in class as an upright rod affecting a test charge x units to the right of it. I thought maybe this would apply to this problem four times over as each of the rods would exert a force perpendicular to it's direction towards the test charge...is this correct, and would someone mind illustrating how I might compute this?
Thanks in advance,
B
