Open the link for circuit diagram
http://i864.photobucket.com/albums/a...me/circuit.jpg
Keeping in view the circuit provided in the link if we find the equivalent resistance of the circuit by using the formula
Equivalent resistance = open circuited voltage/short circuited current
Equivalent resistance = 3V/0.4mA = 7.5kohm
But when we generally calculate the equivalent resistance then the 30kohm resistance and 10kohm resistance are in series because they share only a single node and in this way equivalent resistance comes out to be
Equivalent resistance = 30k + 10k = 40kohm
Why is this difference?