Faraday

Faraday - H.O. Meyer, 12/4/05 Faraday Effect Goal:...

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Unformatted text preview: H.O. Meyer, 12/4/05 Faraday Effect Goal: Magneto-optics: optical activity in a homogeneous medium in the presence of a magnetic field. Measure the material constant that quantifies this effect (Verdet constant) Equipment: Diode laser, coil, controllable current supply, wave generator, photo diode, amplifier, storage scope... 1 Introduction In 1854 M. Faraday found that isotropic media become optically active when a magnetic field is applied in the propagation direction of the light. This was one of the earliest indications that light and electro-magnetism are related. The angle by which the plane of polarization of a linearly polarized beam is rotated is given by = dl B V (radians) , (1) where V is the so-called Verdet constant, and B is the magnetic field in the direction of the light, and the integral extends over the full length of the medium (in our case a cuvette with water). In order to understand the effect, it is useful to think of linearly polarized light as the superposition of left- and right-handed circularly polarized light of equal amplitude. If it happens that the index of refraction for left and right light are not the same (this is called circular bi-refringence), then the phase of one component will advance relative to the other by some angle. When recombining the two components, linear polarization results that is rotated by half that angle. Quantum mechanics is needed to understand the reason for the different indices of refraction. Left and right light is really a beam of polarized photons with spin 1 and magnetic substate +1 or 1, respectively. In a magnetic field, the energy levels that can be excited by such photons correspond to slightly different frequencies (discovered by Zeeman). The frequency shift is the Larmor frequency L = (e/2m)B , where e and m are charge and mass of the electron. From this it is quite straightforward to derive the charge and mass of the electron....
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Faraday - H.O. Meyer, 12/4/05 Faraday Effect Goal:...

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