I know the answers, but I don\'t understand it and need to see how to show the w
ID: 1795248 • Letter: I
Question
I know the answers, but I don't understand it and need to see how to show the work.
Physics 212 Exam II Fall 2017 The next three questions pertain to the following situation: Two electrons labeled A and B possess positive charge q=1.6 x 10-1°C, and have mass m = 9,1 x 101 kg. The electrons are accelerated to different velocities and are sent into a region containing a constant, uniform magnetic field of magnitude 1.5 T but with unknown direction. The electrons' initial velocities are in the +x direction, and they enter the B-field region at the origin. Within the field region, they follow curved paths confined to the xy-plane (z = 0), then emerge at different locations on the y-axis: electron A emerges at y = a, and electron B emerges at y = b, where b > a as shown. Uniform B field q=1.6 x 10-19 c m = 9.1 x 10-3 kg B= 1.5 T 6. What is the direction of the uniform magnetic field in the region x>0? a. +x direction (to the right) b. -x direction (to the left) S. ty direction (upward) Kd7+z direction (out of the page) e. Y direction (into the page) 7. We know that the electrons have the same charge and the same mass. What is the ratio of their velocities vwve? a var Va = a/b b. valvg = Valb C. vwvg = /b? 8. If an electric field of magnitude E= 300 V/m is switched on before the electrons enter the field region, then electron Bis observed to move undeflected, in a straight line along the x-axis. The electric field is perpendicular to both the magnetic field and the initial velocity of the electrons, and occupies the same region as the magnetic field. What is the speed of electron B? a. Va - 100 m/s B. VA= 200 m/s C. - 450 m/s d. Cannot move in a straight line at any speed e. VA = 0 m/s 5 of 9 pages (15 problems)Explanation / Answer
given two electrons A and B
q = 1.6*10^-19 C
m = 9.1*10^-31 kg
B = 1.5 T
6. form fleming's left hand rule, current is to the right, force is upwards hence magnetic field is into the plane of the page
option e) into the page
7. now
mv^2/r = qvB
r = mv/qB
so, ra = mva/qB
rb = mvb/qB
hence
va/vb = ra/rb = a/b
hecne option a)
8. E = 300 V/m
now,
qvB = qE
vB = E
vb*B = E
vb = E/B = 200 m/s
va = 200(a/b)