試題詳解

 9. A proton moves around a circular path (radius = 2.0 mm) in a uniform 0.25 T magnetic field. What total distance does this proton travel during a 1.0 s time interval? (m_p = 1.67×10^-27 kg, q = 1.6× 10^-19 C)
(A) 82 km
(B) 59 km
(C) 71 km
(D) 48 km
(E) 7.5 km