Chapter 18, Problem 12P

* A 3.0-g aluminum foil ball with a charge of $\text{+4}\text{.0 }\times {\text{10}}^{\text{-9}}\text{C}$ is suspended on a string in a uniform horizontal $\stackrel{\to }{E}$ field. The string makes an angle of $\text{30°}$ with the vertical. What information about the $\stackrel{\to }{E}$ field can you determine for this situation?