Question

What speed would a +1.00 C particle need to have to travel in a straight line through a 5.00 T magnetic field that is directed into the screen and a 2.00 V/m electric field that is directed from top to bottom?

40.0 m/s
4.00 m/s
0.400 m/s
0.0400 m/s

I will report you if you give a cruddy answer - please explain!

Answer 1

there are 2 forces acting on the particle: magnetic n electric force

the 2 forces must be equal 4 it to travel in a straight line

as it has +1C charge, q, the charge is dropped in the following:

magnetic force = qv x B where v is velocity n B is magnetic field;

x represents cross-product which in this case of 90-deg. is same as multiply

magnet force = v*5

electric force = qE where E is electric field

= 2

as magnet force = electric force

v*5 = 2

v=2/5=0.400m/s

Answer 2

Okay so we need to bring a couple of equations into this

First E =F/q

We have our q and E lets solve for F

F = Eq

So remember th equation

F = qV x B

F = qVBsin(Ф)

The angle is perpendicular so

sin(90) = 1

F = qVB

Solve for V

F/qB = V

Eq/qB = V

Look at that the charges cancel out!

V = E/B

(Fun fact: Thats what they use in mass spectrometers which is why it says the particle should travel in a straight line)

Anyways lets solve this!

V = 2/5

V = 0.4 m/s