Electrons
(e,m) emitted with negligible speed from an electron gun are accelerated through a potential difference
V0 along the
x-axis. These electrons emerge from a narrow hole into a uniform magnetic field of strength
B directed along
x-axis. Some electrons emerging at slightly divergent angles as shown. These electrons are refocused on the
x -axis for second time at a distance
√Nπ2mV0eB2. Find the value of
N ___.