Physics 2112 Unit 12 Today’s Concept: Magnetic Force on Moving Charges Unit 12, Slide 1

Magnetic Force Unit 12, Slide 2 Electric Field Any particle can cause E field Any particle affected by E field Magnetic Field Only moving particle can cause B field Only moving particle affected by B field

Units Unit 12, Slide 3 Earth ~ 0.6 Gauss Frig Magnet ~ 0.01T (100 Gauss) MRI 1.5 ->5.0 Tesla (15,000 – 30,000 Gauss) LHC 8.4 Tesla World’s Record 45 Tesla (National High Magnetic Field Laboratory at Florida State) Units: Telsa (N/(Cm/sec)) Extremely large field so sometimes use Gauss = (10 -4 T)

Cross Product Review Cross Product different from Dot Product is a scalar; is a vector proportional to the component of B parallel to A proportional to the component of B perpendicular to A Definition of Magnitude: | A||B|sin  Direction: perpendicular to plane defined by A and B with sense given by right-hand-rule Unit 12, Slide 4

x y z B F qv Remembering Directions: The Right Hand Rule Unit 12, Slide 5

Example 12.1 (Acceleration of proton) Unit 12, Slide 6 The earth’s magnetic field is pointed roughly 70 o from the horizontal in Chicago. What would the acceleration of a proton be if it were moving at 1% of the speed of light in the horizontal direction?

CheckPoint 2 Three points are arranged in a uniform magnetic field. The B field points into the screen. Unit 12, Slide 7 A positively charged particle is located at point A and is stationary. The direction of the magnetic force on the particle is: A.right B.left C.into the screen D.out of the screen E.zero

CheckPoint 3 Three points are arranged in a uniform magnetic field. The B field points into the screen. Unit 12, Slide 8 Now the positive charge moves from point A toward B. The direction of the magnetic force on the particle is: A.right B.left C.into the screen D.out of the screen E.zero

Motion of Charge q in Uniform B Field x x x x x x x Uniform B into page Force is perpendicular to v Speed does not change Uniform Circular Motion Solve for R : R Demo q qq v F v F v F v F q Unit 12, Slide 9

Example 12.2 (Analysis Magnets) Unit 12, Slide 10 A proton enters the magnetic field of an analysis magnet at Fermilab and it deflected by an angle of  = 10 o. The field has a strength of 0.2T and a length of 2meters. What is the speed of the incoming proton? X X X X X X X   R sin 

Follow up Unit 12, Slide 11 The analysis magnet Photograph of track in bubble chamber (pre 1984) Electronic version of same thing (top quark event at CDF) Question: In the previous example how did you know it was a proton?