PhysicsLAB AP Free Response Question
2000 B7

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A particle with unknown mass and charge moves with constant speed v = 1.9 x 106 m/sec as it passes undeflected through a pair of parallel plates, as shown above. The plates are separated by a distance d = 6.0 x 10-3 m, and a constant potential difference V is maintained between them. A uniform magnetic field of magnitude B = 0.20 T directed into the page exists both between the plates and in a region to the right of them as shown. After the particle passes into the region to the right of the plates where only the magnetic field exists, its trajectory is circular with radius r = 0.10 m.
(a) What is the sign of the charge of the particle? Check the appropriate space below and justify your answer.

____ Positive     ____ Negative     ____ Neutral     ____ It cannot be determined from this information.

 (b) On the diagram above, clearly indicate the direction of the electric field between the plates.

 (c) Determine the magnitude of the potential difference V between the plates.

 (d) Determine the ratio of the charge to the mass (q/m) of the particle.

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