Othello Act 3 Questions

1. At the beginning of 3.3 Othello is completely in love with Desdemona. By the end of that scene, 480 lines later, Othello is ready to murder her for having an affair with Cassio. How have we gone from the first position to the second position so quickly? How does Iago plant the idea of Desdemona's infidelity in Othello's mind, and how does he make it grow?

2. What sort of person is Emilia, and what seems to be the nature of her relationship with her husband Iago? How does Desdemona's handkerchief come into play within that relationship between Emilia and Iago?