Teaching Physics with the Physics Suite Edward F. Redish

Constant current source

We have studied batteries which provide a fixed voltage across their terminals. In that case, we had to examine our circuit and use our physical principles in order to calculate the current through the battery. In neuroscience, it is sometimes useful to use a constant current source (CCS), which instead provides a fixed amount of current through itself . In this case, we have to use our physical principles in order to calculate the voltage drop across the source.

Suppose we have a fixed current source that always provides a current of I0 = 10-6 amps. For the three circuits shown below, find the the voltage drop across the current source. Each resistor has a resistance R = 2000 W. (If you prefer, you may leave your answer in terms of the symbols I0 and R.)

Note to the instructor: This is a refreshing antidote to the traditional over-emphasis on the constant-voltage battery as a power source.

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