Well, most active and passive basses when you don't use EQ are very similar. After all, the front end of your head is basically an active preamp! An active bass merely moves part of that EQ circuit into the bass where it more convenient to adjust while you are playing.
In the Common Application, it says that the Personal Essay should be at least 250 words, and attached on a separate sheet (presumably, if you're submitting it online, you attach a one-page file).
To do any topic justice in an essay format, you would have to write at least four or five paragraphs. Anything less than that would be far too inadequate to be called an essay. Much depends on the length of the essay.