5 Measurement of e/m for Electrons

Modern Physics

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PHY251 - e/m for electrons PHY 251 Measurement of e / m for Electrons Introduction In this experiment you will measure e / m , the ratio of charge e to mass m of the electron. The set-up consists of an evacuated (except for a low pressure of He gas) cathode ray tube which produces a beam of electrons of known energy. The tube contains an electron gun which emits, accelerates, and focuses electrons. The electron beam becomes visible when some of the electrons in the beam excite Helium atoms in their path, which subsequently de-excite with emission of visible-light photons. For an electron charge e and an accelerating voltage V the (non-relativistic) kinetic energy of the electrons is given by: K = 1 / 2 m v 2 = eV . The tube is supported at the center of a pair of large Helmholtz coils producing a uniform magnetic field B perpendicular to the velocity of the electrons. Thus, the electrons will be deflected to trace a circular path with a radius determined by e / m , the accelerating voltage
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This lab report was uploaded on 02/05/2008 for the course PHY 251 taught by Professor Rijssenbeek during the Fall '01 term at SUNY Stony Brook.

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5 Measurement of e/m for Electrons - PHY251 - e/m for...

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