Each note card expresses as many ideas as the researcher decides to record only one idea not more than two ideas one source page's ideas

   One source page´s ideas.

Explanation:

  Note cards are used to organize information when you´re starting a research paper. The information gathered there could be categorized by topic. When you find an interesting fact about the topic you should writing down paraphrasing it. For each topic, you could have as many cards as you want but each one must express only one idea extracted for a source.

  There are four items that the note card must have: Topic, Where you found the information, paraphrased information extracted from the source, source´s page.

  I hope this answer helps you.