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in an electron microscope, a tungstun cathode with work function 4.5 eV is heated to release electrons that are then initially at rest just outside the cathode. The electrons are accelerated by a potential difference to create a beam of electrons with a de Broglie wavelength of 0.038 nm. Assume nonrelativistic apply to the motion of the electrons. calculate the momentum of an electron in the beam, in kg x m/s. calcualte the kinetic energy of an electron in the beam, in joules. calculate the accelerating voltage. suppose the light, instead of heat, is used to release the electrons from the cathode. What minimum frequency of light is needed to accomplish this?

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shelly

  1. There are many parts to this question, and several different physics equations are needed to do the parts.

    I suggest you review how the De Broglie wavelength is related to momentum and Plank's constant, h. That will tell you the momentum, m V. Use the momentum and the electron mass m to get the kinetic energy, KE = (1/2) m V^2. The accelerating voltage V is given by KE = e *V, where e is the electron charge.

    Review the photoelectric effect for the last part. Someone will be happy to critique your work.

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    drwls

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