# lec09 - qE and magnetic force qvB in opposite directions...

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Magnetism If particle’s velocity v perpendicular to B – The magnetic force ( F ) stays perpendicular to v - B plane. –S i n c e F is perpendicular to v , it does no work on the particle. • The particle’s speed ( v ) stays constant • Its direction of motion changes continuously. • The trajectory is a circle – The particle performs uniform circular motion . – The centripetal acceleration is provided by the magnetic force. Newton’s 2 nd law Motion of Charged Particle in Uniform Magnetic Field = r v m v q B 2 q B mv r = ( uniform, into page ) r F r

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Applications Velocity Selector Has both E and B fields Electric force (
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Unformatted text preview: qE ) and magnetic force ( qvB ) in opposite directions – The forces balance each other for particles with velocity v=E/B • Mass Spectrometer – Ions (charge +e ) accelerate through potential difference V . F m =F e F m >F e F m <F e Uniform B field (out of paper) – Ions enter magnetic field ( B ) with velocity ( v ) perpendicular to B . – Detector (located at 2r ) counts only ions with mass ( m ) given by ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = 2 2 1 mv eV ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = r v m eBv 2 V B er m 2 2 2 = Mass spectrum obtained by varying B...
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## This note was uploaded on 12/06/2011 for the course PHYSICS 111&112 taught by Professor Unknown during the Spring '11 term at Ohio State.

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lec09 - qE and magnetic force qvB in opposite directions...

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