The Electrons in a beam are moving at 2.7x108 m/s in an electric field of 16000 N/C. What value must the magnetic field have if the electrons pass through the crossed fields undeflected?

B = 0.07 mT

Explanation:

q = 1.6x10^-19 coulombs

for the electron to pass through the field undeflected the magnetic force acting on it must equal the electrical force due to the electric field

electric force = Eq = 16000 * 1.6x10^-19 newtons

magnetic force = qvB = 1.6x10^-19 * 2.7x10^8 * B

16000 * 1.6x10^-19 = 1.6x10^-19 * 2.7x10^8 * B

B = 0.07 mT (milli tesla)