Transcript
Page 1: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 2: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 3: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 4: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 5: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

1. Moving electric charges produce magnetic fields, B

B measured in Tesla (1T = 104 Gauss)

Earth’s B field ~ 0.5 Gauss

Largest permanent magnet ~ few T

Largest man-made magnet ~ 20 T

2. Magnetic fields exert forces on moving electric charges

Page 6: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

Magnetic Force

• F = qvB if v ┴ B• F = 0 if v ║ B• F = qvB sin, if v makes angle with B• Right hand rule for direction

• In case where v ┴ B, the trajectory is a circle

• In general, the trajectory is a helix

Page 7: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 8: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

Group Problem

• Suppose 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 ).

a) What is the force on the proton? (magnitude and direction )

b) What will be the path of the proton?c) Find the radius of the circular orbit of the

proton

Page 9: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

Forces & Torques on a Current Loop

w

B

F

F

r = (w/2)sin

=IA X

In general, = B sin, where is the angle between (perpendicular to the area) and B

Page 10: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

I

r

B

B

BI

ro

2

,

Right Hand Rule

Page 11: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

Group Problem

• A long straight wire lies along the x-axis and has a constant current of 3A in the + direction.

a) Find B at a point 2m from the wireb) Find B at a point 1.5 m from the wire in the opposite

direction from (a)c) 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.

d) 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

Page 12: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)
Page 13: Moving electric charges produce magnetic fields, B B measured in Tesla  (1T = 10 4  Gauss)

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