How much of my personal statement should be demonstrating knowledge and how much should be past experiences?

Ideally, the two would be able to connect in some way. For example, past experiences volunteering at the local museum could highlight an aspect you particulalry enjoyed in a history lesson, or brought home to you the physical reality of how people lived in the past. If you don't think the two can be linked in any way, then a paragraph on each would be good as long as you could connect your experiences to the course you're applying to. If you don't think you have enough experiences to fill a paragraph then don't worry - you could always mention a book or documentary you saw that really drew your attention. As long as you demonstrate that your interest in the subject extends past lesson time, you are showing that you are committed to the course which is more important than having a rigid structure.