At a particular instant an electron is traveling in the +x direction, with speed

Question

At a particular instant an electron is traveling in the +x direction, with speed 3X105 m/s. At the location of the electron there is a magnetic field of magnitude 0.22 T in the -x direction, due to current running in a nearby coil. What is the direction of the magnetic force on the electron? What is the magnitude of the magnetic force on the electron? magl Additional Materials section 20.1 My 4. 0 -2 points MI4 20.1.020 An alpha particle (consisting of two protons and two neutrons) is moving in a circle at constant speed, perpendicular to a uniform magnetic field applied by some current-carrying coils. The alpha particle makes one clockwise revolution every 74 nanoseconds (see the figure). If the speed is small compared to the speed of light, what is the numerical magnitude B of the magnetic field made by the coils? What is the direction of this magnetic field? Proton Mass Neutron Mass 1.67e-27 kg Proton Charge +1.602e-19 C O out of the page O into the page Additional Materials section 20.1

Explanation / Answer

a) F= q ( B V) sin theta

F = -1.6 x 10^19 ( 0.22 T ) (3 x 10^5) sin 180 = 0 N

Electron will not experience any magnetic force

b)mv^2/ r= qvB

mv/r = qB

m ( 2pir/t) / r = qB

m ( 2pi /t) = qB

1.67 x 10^-27 ( 2 x 3.14 / 74 x 10^-9) = 2 ( 1.6 x 10^-19 ) B

B = 0.44 T

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