Agenda

• This Week– Ch. 27-29– Skip Lab, No Quiz

• Next Week– Finish 29, No Quiz– Review

• Following– Exam II on Monday (2 weeks)– April 6th [Or previous Friday if prefer]

• Sections– 27.1-27.8– 28.1-28.5– 29.1-29.5

Cross ProductHint: Google it!

Multiply along arrowsPositive Values

I,j,k direction unit vectors

Cross Product

Multiply along arrowsNegative Values

Cross Product

a x b =

Quick Solution for 2D or 3D problems

Cross Product

q(a x b) = q[ ]

How Big Are B Fields?

• B Field units: Tesla (T)– One T = 10,000 Gauss (G)

• Earth? – ~ 0.5 Gauss = 0.5x10-4 T

• Fridge Magnet– 10 Gauss = 1mT

• Largest Permanent Magnets– ~ 5,000 Gauss = 0.5T [Rare Earth]

• Largest Electromagnetic Magnets– ~ 10 T [Continuous]– ~ 100T [Pulse]– Superconducting special

Velocity Selector• Create an instrument which allows only electrons with 1keV Energy

to Pass through. Can use E Field & B field• Electric Force: F = qE • Magnetic Force: F = q(vxB)• Hint: Think Constant & Perpendicular• What should E& B be? What direction?• Design This!

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Mass Spectrometer

• Use magnetic Field to control which elements are counted by a mass spectrometer.

• Hint: Keep E field in source/detector areas

– Use Circular motion (FC = mac = mv2/r)

– Start with this design• Create a system that will measure C14 & C12 simultaneously with

two different detectors. Set up so ions enter analysis area with 1keV of KE, and the detector #2 is 2x the distance of detector #1 for maximum selectivity.

Source (Velocity Selector )

d1

d2 = 2 x d1

DET#1 DET#1

Force on Current Carrying Wires• Rank the total force felt by each of the following current carrying

wires. Each wire has an equal amount of current in the same constant B field. Each Wire covers an equal “x” distance

• Hint: Plug in #’s if it helps– #1: Straight Wire, distance 2L

– #2: Straight Wire (length L) + semicircle (radius r)

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L/102L/3

L

L/3

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Velocity Selector• Create an instrument which allows only electrons with 1keV Energy

to Pass through. Can use E Field & B field• Electric Force: F = qE • Magnetic Force: F = q(vxB)• Hint: Think Constant & Perpendicular• What should E& B be? What direction?• Design This!

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