05-10-2009, 08:31 AM
The question also gave a rail resistance, and once this is considered the effect of ballast resistence is non-trivial (see attached diagram) as current is limited in the series circuit by the rail resistance (simple to calculate), but at each and every point along the rail, some current will "leak" out of the series circuit due to ballast resistance, giving the arrangement in my diagram.
I'm sure this arrangement does have a relativley simple equivalent circuit (like the cube of resistors problem), but I wasn't about to try and derive this in the 15 minutes the marks alotted!
I'm sure this arrangement does have a relativley simple equivalent circuit (like the cube of resistors problem), but I wasn't about to try and derive this in the 15 minutes the marks alotted!