# If an electron enters a region of uniform magnetic

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If an electron enters a region of uniform magnetic field only, the force on the electron is given by: e/m = v/(rB) If B is produced by a set of Helmholtz Coils and we know v we can find e/m by measuring r: (x-a)^2 + (y-b)^2 = r^2 Equipment : Electron e/m deflection tube, Pair of helmholtz coil, Ammeter, Magnetic compass, One stand holder for holding the tube and Helmholtz coils, One L.T Power Unit(800) for the coils, One KV power unit (813) for the tube, One set of connecting wires, MATLAB.

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Procedure: Step 1: Set the accelerating potential V to about 3000 V (the same potential is applied between both plates so V = Vp). Adjust the Helmholtz Coil current I for zero deflection. Zero deflection corresponds to the electron entering and leaving the plate region at y=0 cm. Record V and I. Step 2: Turn of the High Voltage power supply. On the panel of the Power Supply 813, connect the bottom black cable (-) to the top red cable (+), i.e. to move the black cable from (-) to (+). Turn the power supply on and set the output back to the same potential V as in step 1. Keep the same current I in the Helmholtz Coils. Step 3: Insert given sample code into Matlab and edit it to fit you experimental voltage, current, and results. Step 4: Suck 2 dicks. And like it. Results:
d = 0.0520 v = 3.8882e+007 ratio_theory = 1.7563e+011 ratio_exper = 1.7912e+011 percent_error = 1.9838 Conclusion: Appendix:

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Xexp = [2 3 4 5 6]*10^-2*cosd(15); Yexp = [.2 .4 .3 .9 1.0]*10^-2; e = 1.6*10^-19; me = 9.11*10^-31; N = 320; R = 6.8*10^-2; I = .27; d = 5.2*10^-2 Vp = 3*10^3; B = 8.992*10^-7*N*I/R; E = .77*Vp/d; v = E/B; v x = 0:.002:0.1; y = -.4: 0.005:0.4; r = 19*10^-2; x = sqrt(2*y.*r - y.^2); plot(x,y,x,-y,Xexp,Yexp,'o') ratio_theory = e/me ratio_exper = v/(r*B) percent_error = (ratio_exper - ratio_theory)/ratio_theory*100

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