In some cases your professor may require you to create a research question rather than just a research topic.
A research question:
Why bother to have a research question?
Characteristics of Research Questions
For example, the question, "How many female characters appear in the Harry Potter series?" is not a research question because it:
The question, "How are female characters portrayed differently in Harry Potter and the Deathly Hallows and Harry Potter and the Sorcerer's Stone?" is a research question because it: