During the Millikan experiment used to determine the charge on the electron, a c

Question

During the Millikan experiment used to determine the charge on the electron, a charged polystyrene microsphere is released in still air in a known vertical electric field. The charged microsphere will accelerate in the direction of the net force until it reaches terminal speed. The charge on the microsphere is determined by measuring the terminal speed. During one such experiment, the microsphere has radius r 5.35 x 10-7 m, and the field has a magnitude E = 4.124 x 104 N/C. The magnitude of the drag force on the sphere is given by FD = 6rv where v is the speed of the sphere and is the viscosity of air ( = 1.8 x 10-5 N·s/m2). Polystyrene has density 1.05 x 103 kg/m3 (a) If the electric field is pointing down and the polystyrene microsphere is rising with a terminal speed of 1.09 x 10-4 m/s, what is the charge on the sphere? 6.54e-19 xC b) How many excess electrons are on the sphere? 2 x electrons (c) If the direction of the electric field is reversed but its magnitude remains the same, what is the new terminal speed? mm/s

Explanation / Answer

Part a.) The drag force Fd= qE=6pi×ita×r×V

q=6×3.14×1.8×10-5×5.35×10-7×1.09×10-4/(4.124×104)

So, q=47.953×10-20C answer.

Part b.) No. of excess electrons are-

n=qe=47.953×10-20×1.6×10-19

n=7.67248×10-38 electrons answer.

Part c.) If the electrical field is become reverse then the terminal speed is become 0.10254×1088 m/sec. Answer

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