The TOEFL iBT has 4 sections.
First let us see the reading section. As you might have gathered by now, this section consists of 3-5 passages. Each passage has 12-14 questions to answer. The subject of the passage varies from elementary subjects like a science class lecture to complex subjects as zoology, advanced physics and others. Your concern is not the subject, but its length. Every passage is about 700 words in length, so be prepared to read some dry passage of 700 words in under 5-8 minutes.