The Lorentz Force

A magnetic field can push on a moving charge, but only sideways — perpendicular to both its velocity and the field itself. This sideways push never speeds the charge up or slows it down; it only bends the path, curving it into a circle if the field stays constant.

F = q · v · B

• F — force (N): the sideways magnetic push on the charge
• q — charge (C): the amount of electric charge carried by the particle
• v — velocity (m/s): how fast the charge is moving, here perpendicular to the field
• B — magnetic field (T): the strength of the magnetic field the charge moves through

A charged particle with a charge of 2 coulombs moves at 3 meters per second, perpendicular to a magnetic field of 5 tesla. What force does it feel?

• q = 2 C
• v = 3 m/s
• B = 5 T

1. F = q · v · B
2. F = 2 C · 3 m/s · 5 T

F = 30 N

The same 2 coulomb charge now moves at 3 meters per second through a stronger 10 tesla field. What is the force on it?

• 30 N
• 15 N
• 60 N

A positive charge moves to the right through a magnetic field pointing into the page. Which way does the magnetic force push it?

• Upward
• Downward
• Forward, in the same direction it's already moving