A monochromatic light (wavelenght 2000 A) shines on an Aluminium surface (W 4.2 eV)1) which is the maximum value for the energy an expelled electron may have? Ok this one is easy, it would be h.c/wavelenght - W2) And the minimum? Here is where i have a problem, i thought all electrons expelled would have the same kinetic energywhat would make it vary from electron to electron? maybe that said electron collided/got slowed down by another electron's electrical force?So which would the the minimum? 0, since a stationary free electron has that energy, and any less would mean it's still bound to the atom?3) i don't know how it's called in english but they ask me to determine the potential the surface must have in order to retain all the electrons the light kicks out.I THINK it's as easy as determining the maximum energy for an expelled electron in electron-volts, and dividing it by the electron's charge (the number would stay the same)Is it like that?
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2) The emitted electrons have a range of kinetic energy, from zero to the maximumThis is because electrons from just BELOW the surface can be knocked out - these can then lose some or all of their kinetic energy due to collisions with metal atomsSo the answer is zero3) Yes, you are almost correctTo prevent the electron escaping (to infinity - i.ezero potential), the surface must be sufficiently positive so that the work done moving electron from the surface to 0volts kinetic energy lostWhat happens is shown in the diagram in the linkElectrons are simply pulled back if the surface potential is sufficiently positiveIf the maximum kinetic energy of the expelled electron is 10eV for example, the potential of the surface must be at least +10V to ensure all electrons get pulled back This follows from the definition of the electron-voltThe potential in volts is numerically equal to the maximum energy in electron-volts.
