A Proton Having a Speed Of $3.0 \times 10 ^ { 6 } \mathrm {~m} / \mathrm { s }$

Multiple Choice

A proton having a speed of $3.0 \times 10 ^ { 6 } \mathrm {~m} / \mathrm { s }$ in a direction perpendicular to a uniform magnetic field moves in a circle of radius $0.20 \mathrm {~m}$ within the field. What is the magnitude of the magnetic field? $( e$ $= 1.60 \times 10 ^ { - 19 } \mathrm { C } , m _ { \text {proton } } = 1.67 \times 10 ^ { - 27 } \mathrm {~kg}$ )

A) $0.16 \mathrm {~T}$
B) $0.080 \mathrm {~T}$
C) $0.24 \mathrm {~T}$
D) $0.36 \mathrm {~T}$
E) $0.32 \mathrm {~T}$