Look at Lec 13 (part 2) Slide #1 to answer this question. This is about a charged particle moving in a circular path in an external magnetic field pointing into the page. The answer for part (a) is that the charge is negative. How can we figure out that the charge is negative by looking at the path of the circle? A charge moving in a circular path in an external magnetic field The charge is negative because using RHR #2, the charge is generating a magnetic field into the page. A magnetic field into the page is considered negative. The charge could be positive or negative. It is impossible to state that correctly unless we know the magnitude of the magnetic field B. The question just made an assumption, for no reason at all. The charge is negative because it is moving in a circular path in a magnetic field. A positive charge does not move in a circle in an external magnetic field. Using RHR #1 we see that the charge would have moved in a counterclockwise circle if it was a positive charge. Since the charge is moving in a clockwise circle, it must be a negative charge. None of the answer choices is correct.