Question

At a given instant, the force on an electron is in the +z-direction (out of the page), which the electron is moving in the +x-direction (to the right). What can we say about the B field responsible for this force on the electron? (The y-direction is up on the page.)

Answer 1

Answer:

The direction of the B-field is in the +y-direction.

Explanation:

The corresponding formula is

$F_B = qv\times B$

This means, we should use right-hand rule.

Our index finger is pointed towards +x-direction (direction of velocity),

our middle finger should point towards the direction of the B-field,

and our thumb should point towards the +z-direction (direction of the force).

Since our middle finger in this situation points towards +y-direction, the B-field should be in +y-direction.

$\^{x} \times \^{y} = \^{z}$