physics lab 10

# When an electron beam is produced by the electron gun

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magnetic field. When an electron beam is produced by the electron gun, the low-pressure Helium appears as a circular trace and its magnitude can be approximated by using the built in cm ruler which determines diameter readings. Cathode K is heated, releasing heated electrons, the motion of the electrons is accelerated by the electric potential (V) ( all this can be seen by figure 2 in appendix A); applied between anode P and Cathode K. Using the law of Conservation of Energy, the velocity of the electrons accelerated by V can be determined with the equation: (1) which results in: (2) Where the mass of the electron (m) is measured in kg and the electrical charge of the electron (e) is measured in C. A Lorentz Force F = evB (3) is established due to the electrons perpendicular motion with velocity (v) to the uniform magnetic field (B). This force gives the electrons their circular path in a plane perpendicular to that of the magnetic field’s. Establishing a magnetic field with magnetic flux density equal to B [b/m 2 ], we can obtain the equation (4) Where r is the radius and v is the velocity of the circular motion respectively. From the previous equation, we determine , (5) which allows for the calculation of the charge to mass ratio, or e/m, being (6)

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