Moving electric charges produce magnetic fields, BB measured in Tesla (1T = 104 Gauss)Earths B field ~ 0.5 GaussLargest permanent magnet ~ few TLargest man-made magnet ~ 20 T2.Magnetic fields exert forces on moving electric charges

Magnetic Force F = qvBif v BF = 0if v BF = qvB sinq,if v makes angle q with BRight hand rule for direction

In case where v B, the trajectory is a circleIn general, the trajectory is a helix

Group ProblemSuppose a proton has a velocity v = 106 m/s to the right perpendicular to a uniform magnetic field B = 2 T (take B directed up out of the paper ). What is the force on the proton? (magnitude and direction )What will be the path of the proton?Find the radius of the circular orbit of the proton

Forces & Torques on a Current LoopIn general, t = mB sinq, where q is the angle between m (perpendicular to the area) and B

=IA

r( = (w/2)sin

w

F

F

B

X

B

B

I

r

Right Hand Rule

Group ProblemA long straight wire lies along the x-axis and has a constant current of 3A in the + direction.Find B at a point 2m from the wireFind B at a point 1.5 m from the wire in the opposite direction from (a)Find the force on an electron located at the point in (a) and moving with a velocity of 3 m/s perpendicularly away from the wire.Find the force/length on a second long straight wire lying parallel to the first 3 m away and having a current of 2A in the opposite (-) direction

Chapter 18