A proton starting from rest travels through a potential of 1.0 kV and then moves into a uniform 0.040-T magnetic field. What is the radius of the proton's resulting orbit? (mproton=1.67 * 10-27 kg, e = 1.60 * 10-19 C)

In the region of potential difference, protons will acquire velocity which can be found as follows

1/2 m v² = Ve, V is potential diff, v is velocity attained, m is mass of proton, e is charge on proton

v² = 2Ve / m

For circular path of proton in a magnetic field

mv² / r = Bev r is radius of circular path.

r = mv / Be

r² = m²v² / B²e²

= 2Ve/m x m² / B²e²

= 2Vm / B²e

= 2 x 1000 x 1.67 x 10⁻²⁷ / (.04² x 1.6 x 10⁻¹⁹)

=.013

r =.114 m

= 11.4 cm