Question

At a location near the equator, the earth’s magnetic field is horizontal and points north. An electron is moving vertically upward from the ground. What is the direction of the magnetic force that acts on the electron?(a) North (b) East (c) South (d) West (e) The magnetic force is zero.

Answer 1

Answer:

(b) EAST

Explanation:

you can assume that the magnetic field points rightward, that is, in the positive x direction (NORTH). Furthermore, you can assume that the direction of the motion of the electron is in the positive y direction. Hence, you have:

$\vec{B}=B_o\hat{i}\\\\\vec{v}=v_o\hat{j}$

You use the Lorentz formula to known which is the direction of the magnetic force over the electron:

$F=qv\ X\ B$

which implies the cross product between the unitary vecors j and i, that is

$\hat{i} \ X\ \hat{j} = -\hat{k}$  (WEST)

However, the minus sign of the charge of the electron changes the direction 180°. Hence, the direction is k. That is, to the EAST

Answer 2

Answer:

The electron will move east.

Explanation:

According to fleming's left hand rule for when the field and current are at right angles, the first finger represents the field's direction ( north to south), the second finger represents the current direction ( + to -) and the thumb represents the direction of motion..

See image below.