Title: Understanding Coulomb's Law Learning Target: To interpret and apply Coulomb's Law Discussion: Answer the following questions. State the reason for your answer. 1. If two charges are fixed such that the distance r between them does not change, but the charge q₁ is increased, will the electric force become stronger or weaker? 2. If the charges are not changed, but they are moved farther apart (the distance r becomes bigger), will the electric force become stronger or weaker? 3. Which is stronger, the electric force or the gravitational force? Give a numerical example to support your answer. Exercises 1. If the distance between two negative charges is reduced to one-third the original distance (r new =1/3 r old), what will be the new electric force of repulsion F new compared with the old force F old? 2. Two opposite charges -q₁ and +q2 are 1 m apart. A third charge q3 is placed along the line joining q₁ and q2. If q3=q2= 2q1, find the exact position of q so that it feels no net electric force. Application Robert Millikan in his famous oil drop experiment was able to determine the charge of an electron. Draw a force diagram for the oil drop, discuss balance of forces in the experiment, and explain briefly how Millikan was able to achieve his aim in the experiment.