I had a problem in my physics class today involving Kirchhoff's current law in a circuit. I made a quick drawing showing the circuit arrangement in the problem:

My question isn't about how to calculate the actual values of I1, I2, and I3, but how to figure out their signs. Because there is a battery on each side of the circuit, I expected that I1 and I3 would both be negative, since current flows from the batteries in the direction opposite than that shown by the arrows in the drawing. But according to my physics book, I1 is negative and I3 is positive (and I2 is also positive, which I expected). How can this be true?

My question isn't about how to calculate the actual values of I1, I2, and I3, but how to figure out their signs. Because there is a battery on each side of the circuit, I expected that I1 and I3 would both be negative, since current flows from the batteries in the direction opposite than that shown by the arrows in the drawing. But according to my physics book, I1 is negative and I3 is positive (and I2 is also positive, which I expected). How can this be true?

Last edited: