Question

A beam of charged particles enters a magnetic field and travels in a helical or spiral path. What does the shape of the path indicate about the initial velocity of the particles?

A. The initial velocity is parallel to the magnetic field
B. The initial velocity has components both parallel and perpendicular to the magnetic field
C. The initial velocity is perpendicular to the magnetic field
D. The initial velocity has greater magnitude than particles traveling in a circle through the magnetic field

Answer 1

B. The initial velocity has components both parallel and perpendicular to the magnetic field

Step-by-step explanation:

A moving charged particle can be deflected by a magnetic field, only when some component of its velocity is perpendicular to the direction of the magnetic field.

A particle will move in a circular path when it has only one velocity component and it is perpendicular to the magnetic field. If the particle has a component that is parallel to the magnetic field, its magnitude and direction is not altered since
`B\cdot v = 0`; The result is a circular orbit in the plane perpendicular to the magnetic field, and straight line motion parallel to the magnetic field—a helical path.