By the use of twoport network theory, the classical expression for the two-species Hall Coefficient,
is, on admission of terms neglected by earlier authors, corrected to
The new expression approximates the old when |By| « min {1/μn, 1/μp}. The condition of approximation establishes the range of field strength in which the classical expression is acceptable. Since the Hall Effect is part of the stock-in-trade of electrical engineers, however, it seems important that students should be aware of the correct expression.