1. An electron which moves with a speed of 3 x10⁴ m/s parallel to a uniform magnetic field of 0.40 T experiences a force of what magnitude? (q_e = 1.6 x10^-19 C)

ans: zero; no magnetic force when moving parallel to B.

2. A proton moving with a speed of 3 x10⁵ m/s perpendicular to a uniform magnetic field of 0.20 T will follow which of the paths described below (q_p = 1.6 x10^-19 C and m_p = 1.67 x10^-27 kg)?

ans: a circular path of 1.5 cm radius; the perpendicular force is q*v*B, and the accel is q*v*B/m = v*v/r. Solve for r = m*v/q*B.

3. Two singly ionized isotopes, X and Y, of the same element move with the same speed perpendicular to a uniform magnetic field. Isotope X follows a path of radius 3.35 cm while isotope Y follows a path of radius 3.43 cm. What is the ratio of the two isotope masses, m_X/m_Y?

ans: 0.977; use r = m*v/q*B from above. The only thing that changes is r, so m1/m2 = r1/r2.