This is an excellent PowerPoint that both introduces and quizzes students over the three parts of author's purpose. The first few slides explain author's purpose, the three separate parts, and examples of each. The rest of the slides interactively quiz your class by having them differentiate the three parts of author's purpose (persuade, inform, entertain) using short and interesting paragraphs.
My kiddos loved this PowerPoint! I had them use their miniature white boards to display their answer choices. I would give them about a minute per slide and have them think about why they selected their answer choice. I would then have them display their boards, we would discuss the answer, and choose the answer choice on the PowerPoint according to majority rule. They had a blast!