Question

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

a.the charge is negative and speeding up
b.none of these
c.the charge is negative and slowing down
d.the charge is positive and slowing down
e.the charge is positive and speeding up

Answer 1

\(r=\frac{m v}{B q}\)

Since the radius is decreasing, the charge must be slowing down.

and because it follows a clockwise spiral it must be a negative charge.