An electron is travelling in the positive x direction.A uniform electric field is in the negative y direction.If a uniform magnetic field with the appropriate magnitude and direction also exists in the region, the total force on the electron will be zero.The appropriate direction for the magnetic field is:
A)the positive y direction
B)the negative y direction
C)into the page
D)out of the page
E)the negative x direction

Question

An electron is travelling in the positive x direction.A uniform electric field  is in the negative y direction.If a uniform magnetic field with the appropriate magnitude and direction also exists in the region, the total force on the electron will be zero.The appropriate direction for the magnetic field is: 
A)the positive y direction 
B)the negative y direction 
C)into the page 
D)out of the page 
E)the negative x direction

Quizplus · Accepted Answer

The force on a charged particle moving in a magnetic field is given by the formula:

F = qvB sin(theta)

where 'q' is the charge of the particle, 'v' is the velocity of the particle, 'B' is the magnetic field, and theta is the angle between the velocity and the magnetic field.

In this case, the electron is travelling in the positive x direction and the electric field is in the negative y direction. Since the electric field is perpendicular to the magnetic field, the magnetic force will be perpendicular to both the velocity and the electric field.

To cancel out the electric force, the magnetic force must be equal in magnitude but opposite in direction. Since the magnetic force is perpendicular to the velocity, the angle theta must be 90 degrees. To achieve this, the magnetic field must be into the page, which is perpendicular to both the x direction of motion and the y direction of the electric field. Thus, the correct answer is C: into the page.

An Electron Is Travelling in the Positive X Direction