# Force on Moving Charges in a Magnetic Field

1. Aug 13, 2008

### Number1Ballar

1. The problem statement, all variables and given/known data
Consider the example of a positive charge q moving in the xy plane with velocity $$\hat{v}$$ = vcos($$\theta$$)$$\hat{x}$$ + vsin($$\theta$$)$$\hat{y}$$ (i.e., with magnitude v at angle $$\theta$$ with respect to the x-axis). If the local magnetic field is in the +z direction, what is the direction of the magnetic force acting on the particle?
Express the direction of the force in terms of $$\theta$$, as a linear combination of unit vectors, $$\hat{x}$$, $$\hat{y}$$, $$\hat{z}$$.

2. Relevant equations
Cross product.
$$\vec{C}$$ = $$\vec{A}$$ X $$\vec{B}$$ = (AxBy - AyBx)$$\hat{z}$$ + (AyBz - AzBy)$$\hat{x}$$ + (AzBx - AxBz)$$\hat{y}$$

3. The attempt at a solution
I don't know what to plug in, and overall am just confused as to what the formula means.

Any explanation would be greatly appreciated!

2. Aug 13, 2008

### Defennder

You only need to to apply the equation for the Lorentz force here. What have you learnt about how to evaluate the cross product of two vectors?