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Unformatted text preview: Physics 325 Spring 2011 Discussion 3 February 7, 2011 Let us revisit the example of a charged particle (mass m , charge q ) in a uniform constant magnetic field ~ B = B z . This time, we use the cylindrical coordinates ( r,,z ) . (a) Write down the equations of motion in cylindrical components ( v r , v , and v z ). Start from ~v = v r r + v + v z z and take time derivative of both sides. Remember that both r and have non-zero time derivative. (b) Suppose the initial velocity is given, with v z = 0 at t = 0 . Without loss of generality, we can choose the origin of coordinates such that v r = 0 at t = 0 . Let v =- u at t = 0 . Even with this restriction, we still have a freedom to choose the value of r at t = 0 . What should we choose for r at t = 0 such that we have v r = 0 initially? (c) Solve for v r ( t ) and v ( t ) with the initial conditions from part (b)....
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