Chapter 26 Problem Solns - Chapter 26 21) A velocity...

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Chapter 26 21) A velocity selector uses a 60-mT magnetic field perpendicular to a 24-kN/C electric field. At what speed will charged particles pass through the selector undeflected? Answer: In a velocity selector only particles with a certain velocity will have a balance between the magnetic force and the electric force and only those particles will pass through. F E = F M => qE = qv × B=> qE = qvB => v= E/B => v= (24kN/C)/(60mT) = 4 × 10 5 m/s 23) How long does it take an electron to complete a circular orbit at right angles to a 1 G magnetic field? Answer: So what is happening is a particle comes into the magnetic field and then feels a force perpendicular to its motion which sends it into circular motion. What is interesting to note is that they don’t tell you the velocity so it will probably the case that velocity does not matter. The centripetal force on the particles is the magnetic force. mv 2 r = qv × B => v r = qB m What is the value v/r though? v/r is just the angular velocity. Thus w = v r = qB m In order to complete a circle we pass through 2 π radians. wt = 2
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This note was uploaded on 10/26/2008 for the course PHYSICS 8B taught by Professor Shapiro during the Spring '07 term at University of California, Berkeley.

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Chapter 26 Problem Solns - Chapter 26 21) A velocity...

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