# Vector evaluation & Lorentz force 02

## Homework Statement

An electron in electric & magnetic fields;
E = 3.0x107 ex NC-1
B = 3.0 ez T
has velocity
v = 1.0x10^7 (2ex-ey)

Calculate em force on the electron.

## Homework Equations

I'm using the Lorentz force law here.
F = q(E + v X B)

I have an example solution using vectors to evaluate direction

| ex_______ey_______ez |
| 2.0x107_ 1.0x107 __ 0 |
| 0_______0________3.0 |

## The Attempt at a Solution

I think this has been posted as the solution to vXB,but then why is the E value 3.0 T there???

Could someone please ecplain why this is.

Last edited:

TSny
Homework Helper
Gold Member
I have an example solution using vectors to evaluate direction

| ex_______ey_______ez |
| 2.0x107_ 1.0x107 __ 0 |
| 0_______0________3.0 |

## The Attempt at a Solution

I think this has been posted as the solution to vXB,but then why is the E value 3.0 T there???

Could someone please ecplain why this is.

3.0 T is the B value, not the E value.

Oops, a typo, yes, but why is it there, how does it relate to the Lorentz law & is the solution

Final calculation 9.6x10-12 N

I seem to not be able to attach workings in a picture file, sorry.

TSny
Homework Helper
Gold Member
The determinant will give you the cross product of v and B. The result of the determinant will be a vector. You then need to add the vector E to v x B and finally multiply by q.

OK
vXB = ex (3.0x107 - 0) + ey (-6.0x107 - 0) + ez (0)

q(vXB)= -e (3.0x107 ex + (-3.0x107 ex - 6.0x107 ey) + 6.0x107 * 1.6x10-19 ey) N

F = 9.6x10-12 ey N