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At 1:09 PM -0400 4/27/06, Michael Edmiston wrote:
Here is another example about how I think students view equations.
Consider the equation typically referred to as Ohm's Law. Should we
write it as R = V/I, V = IR, or I = V/R? Note that some textbooks
introduce R = V/I as the definition of resistance.
However, when students first encounter this, what experiences, if any,
have they had? They know that batteries have a particular voltage and
they most likely have been taught to think of this voltage as a type of
pressure. They also know that wires and other electrical devices have
resistance to the flow of current. Therefore, if we present the
equation I = V/R it immediately makes sense to them. They view the
voltage as causing the current, and they view R as restricting the
current, so voltage in the numerator and resistance in the denominator
makes intuitive sense to them.
Therefore I first introduce it as I = V/R so they can see the logic of
it.
I have a book on my desk which says, "Note: we could write the equation for
Ohm's law as \Delta V = IR, but I = \Delta V/R is a better description of
cause and effect because it is the potential difference that causes the
current."
Would you agree there is a cause and effect relationship here?
Larry