What is the difference between a test charge (q) and a point charge (Q) in electrostatics (physics)?

Question

I tried to google this, but there is no good explanation.

In: 2

Answer 1

A point charge, Q, is an actual charge…it has it’s own field, it just has no size.

A test charge is fictitious/virtual…you’re saying “What would happen to this charge *IF* I put it here?”, not “I’m actually putting a charge here.” A test charge doesn’t influence the rest of the setup, a point charge does.