I have been asked the following question in a problem sheet:

A $100mm$ diameter, $0.5mm$ thick silicon wafer at room temperature has a charge carrier density of $1.5×10^{10} cm^{-3}$. A potential difference is applied across the wafer, and the charge carriers are seen to move through the wafer at $844 ms^{-1}$. What is the flow rate of charge through the medium?

This seems simple; just use $I=nAev$ where $v$ is the drift velocity and where I have assumed that the question refers to current when it says "the flow rate of charge through the medium". Firstly is it right to assume that this is the current. Secondly, surely the drift velocity isn't $844ms^{-1}$ or do I just assume it is? I can't see another way of doing it without assuming that.

Then the following part of the question asks "what is the electric current?". Is it just the same answer as the above?

  • $\begingroup$ Is the potential difference applied across the thickness (.5mm direction) or the across diameter of the wafer? $\endgroup$ – Sam Bader Apr 2 '15 at 20:14
  • $\begingroup$ The question doesn't make that explicitly clear but I think that it's reasonable to assume that it's applied across the flat face of the wire as you asked $\endgroup$ – RobChem Apr 2 '15 at 20:24

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