Question

An electron is traveling horizontally from the northwest toward the southeast in a region of space where the Earth's magnetic field is directed horizontally toward the north. What is the direction of the magnetic force on the electron?

Short answer

Answer: The direction of the magnetic force on the electron is downward.

Step-by-step solution

Understand the given information and problem

We know an electron is traveling horizontally in the Earth's magnetic field. Due to their negative charge, moving electrons experience a force within a magnetic field (Lorentz force). Determine the force's direction.

Identify the directions of movement and magnetic field

The electron is moving from the northwest to the southeast. The Earth's magnetic field points horizontally towards the north.

Apply the left-hand rule or right-hand rule for electrons

Remember, we use the left-hand rule for electrons, contrary to the right-hand rule of conventional current flow. To apply the left-hand rule, stretch your left hand with thumb, index, and middle fingers perpendicular to each other. Your thumb represents the electron's motion, your index finger represents the magnetic field, and your middle finger represents the magnetic force.

Align your left hand with the movement and magnetic field

Point your thumb along the direction of electron movement, from the northwest toward the southeast. Point your index finger in the direction of the magnetic field, which is horizontally towards the north.

Observe the middle finger's direction

After aligning your thumb and index finger according to the electron movement and the magnetic field, your middle finger will point downward. This indicates that the magnetic force on the electron is in the downward direction. So, the direction of the magnetic force on the electron is downward.