Answer the following question given this paragraph: 

So does the magnetic force cause circular motion? Magnetic force is always perpendicular to velocity, so that it does no work on the charged particle. The particle’s kinetic energy and speed thus remain constant. The direction of motion is affected, but not the speed. This is typical of uniform circular motion. The simplest case occurs when a charged particle moves perpendicular to a uniform B -field, such as shown in Figure 22.20. (If this takes place in a vacuum, the magnetic field is the dominant factor determining the motion. ) Here, the magnetic force supplies the centripetal force F c = mv 2 / r . Noting that sin θ = 1 , we see that.


Q: Magnetic force is always perpendicular to what?

 Choices:

- speed

- sunlight

- length

- velocity

A:
velocity
