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Forces on Charges

Learn about charge motion in magnetic fields, wire observations, WebAssign updates, gradebook progress, upcoming quiz, magnetic field calculations, right-hand rule, magnetic forces, magnetic field effects on charges, and more detailed physics topics.

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Forces on Charges

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  1. Forces on Charges Spinning Around Again

  2. Here we are again: • Today we will have a discussion about charge motion in magnetic fields and so some observations of wires in magnetic fields. • There is A new WebAssign (Aren’t you excited??) posted. • I am still working on the gradebook so you can see your grades all together. • Friday will be a Quiz on this week’s work. Maybe last week’s too! • Next week more of the same.

  3. Last Session: • F=Bqv Sin(B,V) • Right hand rule for direction.

  4. A LONG, STRAIGHT WIRE VECTOR! permeability of free space

  5. What is magnetic field at X?? B X 1 Meter 450  1 Ampere Current OUT of Paper DIRECTION? “NW”

  6. REMEMBER:The effect of the sign of a moving Positive and negative charges will feel opposite effects from a magnetic field.

  7. The Velocity Selector

  8. Let’s Look at the effect of crossed E and B Fields: x x x B E x x x v • q , m

  9. x x x B B E E x x x v • q m v = E / B What is the relation between the intensities of the electric and magnetic fields for the particle to move in a straight line ?. FE = q E and FB = q v B If FE = FB the particle will move following a straight line trajectory q E = q v B FB FE •

  10. A charged particle is injected into a Magnetic Field. Can the field do WORK on the particle? A YES B NO C It depends on the direction the particle is moving in with respect to the field. D I want to go back on Spring Break!

  11. The Motion of a Charged Particle in a Magnetic Field The electrical force can do work on a charged particle. Parabola The magnetic force cannot do work on a charged particle.

  12. The Motion of a Charged Particle in a Magnetic Field The magnetic force always remains perpendicular to the velocity and is directed toward the center of the circular path.

  13. 21.4 The Mass Spectrometer magnitude of electron charge KE=PE

  14. Smaller Mass Mass Spectrometer

  15. Kratos Profile HV-3 Gas Chromatograph & Direct Probe Mass Spectrometer Description Medium resolution double focusing (E/B) magnetic sector mass spectrometer with gas chromatograph and direct probe inlets; electron impact and chemical ionization sources.

  16. EXAMPLLE: Molecular structure and mass spectrum of 1-acetyl-4-(2-pyridyl)piperazine. The mass spectrum was obtained with a Perkin-Elmer ion trap detector.

  17. An Example A beam of electrons whose kinetic energy is K emerges from a thin-foil “window” at the end of an accelerator tube. There is a metal plate a distance d from this window and perpendicular to the direction of the emerging beam. Show that we can prevent the beam from hitting the plate if we apply a uniform magnetic field B  such that

  18. r Problem Continued

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