Answer:
B.(4.9 × 10-14 newtons) · sin(30°)
Explanation:
The magnetic force exerted on charged particles by a magnetic field is given by

where
q is the charge
v is the speed of the charge
B is the magnetic field intensity
is the angle between the direction of v and B
The first beam moves at right angle to the magnetic field, so
and the force on this beam is simply
(1)
The second beam moves at angle of
. The electrons are travelling at same speed v, and the magnetic field is still the same (and the charge q is also the same, since they are electrons as well), so the magnetic force in this case is
(2)
But from the previous equation we know that

so, if we substitute into eq. (2), we find
