Question

(2) Charged pith balls hang from strings and repel each other as shown in the photograph. Assume the pith balls have equal mass and equal negative electric charge. The mass of each pith ball is O grams. The length of one string is 6.0 cm + 0.2 cm. The half-opening angle is 10" +1 (a) Estimate the number of excess electrons on one pith ball, include an estimate of the uncertainty in that number. Suggestion: start by deriving a symbolic expression for q, using the small angle approximation. Take a peek at HRW Problem 21-42 if that helps (but you must derive your own result, not use that as a starting point). Then, using the symbolic expression, check which variables q is sensitive (high powers) and insensitive (low powers) to. You may neglect small fractional uncertainties which in this case means taking the leading uncertainty only. Express your answer as q δq measured in units of e. Reminder: the master formula for propagation of uncertainties is: of oc b(ab This is for a quantity f(a, b, c,.. that depends on a,b.c..

Answer 1