# direction problem.

A unfiorm electric field of 1.86 X 10^4 V/m and a uniform magnetitc field of 2.62 X 10^-3 T are oriented at right angles to each other in an empty region of space.

a) if a beam of electrons passes through these fields at right angles to both of them what is the speed of the electrons if they experience no deflection?

b) if the electrons are traveling in the +x direction of a right - handed ( x, y, z) coordinate system, and the magnetic field points in the +y direction, what is the direction of the electric field?

i dont know how to do b..that is not +z direction

### 1 個解答

• 最愛解答

(b) The beam of electrons are moving in the +x direction, thus the direction of conventional current is flowing in the -x direction.

Since the magnetic field lines are pointing in the +y direction, by using Fleming's Left Hand Rule (Motor Rule), the magnetic force is acting at the -z direction.

Hence, the electric force acting on the electrons should be pointing at the +z direction in order to balance the magnetic force. Therefore, the electric field lines act in the -z direction, as electrons go against the electric field lines.