Lecture 20 - Applications. Magnetic force on a current

# Lecture 20 - Applications. Magnetic force on a current -...

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1 Lecture 20 Applications Applications. Magnetic force on a current ACT: Direction of magnetic force The B field is directed toward the board. What is the direction of the force when the electrons are just coming out of the emitter (gray part)? Helmholtz coil electron beam A. Toward you B. To the left C. To the right DEMO: Electron beam in Helmholtz coils e - B F v FqvB Circular motion in a uniform field •un iform is initially perpendicular to Uniform circular motion Fma 2 m centripetal R 2 qvB mv qB Helix If the initial velocity of the charges is NOT perfectly perpendicular to B… F

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2 Particle accelerators Like the Large Hadron Collider (LHC) at CERN Huge magnets keep the particles moving in circles. In some sections, electric fields (NOT magnetic fields) accelerate the particles E Magnetic fields cannot do work! B mv p R qB qB  Measuring the mass of a particle in an accelerator Measuring the curvature of a path is the usual way of measuring momentum of particles in high energy experiments. mv p R qB qB negative particle into screen positive particle e + e - B Thompson’s q/m experiment mv R qB Radius of circular trajectory of charge q in uniform field B: Charge acquires its speed between two plates with potential difference V: 2 2 1 2 qV v m 
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## This note was uploaded on 09/21/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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Lecture 20 - Applications. Magnetic force on a current -...

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