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# Charge To Mass Ratio For An Electron

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Introduction

Physics Formal Lab Charge To Mass Ratio For An Electron Professor: Dr.Kilner Ta: Mr.Laderman Done by: Amir Mofidi 010238350 Section 004 Abstract How electrons behave in the presence of a magnetic field was the purpose of this lab. In particular, how there is a force acting on the electron in a magnetic field related to its velocity; or in other words the force acting on the electrons will cause them to move in a circular path. Measuring the charge to mass ratio of an electron using an apparatus which fires electrons into a uniform magnetic field produced by Helmholtz coils; the particles follow a circular path. The anode voltage was set at 200v; the radius of the curvature of the electrons was changed by adjusting the Helmholtz coils current. Its radius ranges from 11cm to 6 cm; the strength of the magnetic field and the speed of the moving particles, one can figure out the charge to mass ratio. The value found for the ratio of electrons to mass to in this experiment would be 1.89�1011 coulombs/kg. Comparing this experimental value to the theoretical value which is 1.76�1011 coulombs/kg makes a 7.38% experimental error. ...read more.

Middle

To observe the circular motion of an electron beam in a nearly-uniform magnetic field and deduce the charge-to-mass ratio of the electron from measurements of the orbital radius. Based on theoretical calculations and experimental evidence, both the charge and the mass of an electron are constants, as is the ratio of the two. The magnetic field will induce a force on the electron which is perpendicular to both the direction and the magnetic field, and will force the electron beam to curve. The radius of curvature can be used to calculate the charge-to-mass ratio, since the curvature is directly related to both the mass of the electron and its charge. Method In this experiment the equipments were set up as in figure3. Figure 3 At the base of the e/m apparatus are inputs for the heater filament voltage (the cathode from which the electrons will be emitted), the anode voltage (the voltage through which the electrons will be accelerated), and the Helmholtz coil current. 6 volts from the output of the power supply was applied to the heater inputs located on the base of the e/m apparatus. The discharge tube power supply was turned on and the cathode glow red hot. ...read more.

Conclusion

It is fair to say that this simple experiment sparked a line of research which drastically changed our way of thinking about the universe. Aside from the thrill of repeating an important and historic experiment, this lab is an ideal forum for exploring the motion of charged particles in electric and magnetic fields. At the end of the day, it is to be known how to calculate the electromagnetic force on a particle in any field configuration. Conclusion In this experiment you will observe the behavior of electrons in a magnetic field and determine a value for the electron charge-to-mass ratio e/m. Although it ended up with a 7.38% error it is still an acceptable value for this experiment. The final observed value for e/m turned out to be 1.89�1011 coulombs/kg. Considering the inherent difficulties associated with the experiment, the results are astonishingly accurate. One difficulty was accurately measuring the radius of the beam on the ruler due to that the room was not dark enough and it made it hard to see the exact radius of the beam. Second the Helmholtz coils where not orient parallel to the direction of the earth's magnetic filed (about 15? east of geographic north); so the effect of the earth's magnetic filed was not minimized and it had its effects in this experiment. At the end it was very interesting lab with very good results. ...read more.

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