Physics Kirchhoff's loop rule. Help Please!?

For ideal voltage sources when you are tracing the loop in the assumed direction of current and it passes through the voltage source from negative to positive...YOU ADD THE VOLTAGE of the voltage source.

Should you be tracing against current...or should assumed current flow opposite the source's preferred direction, you subtract the voltage source's voltage.

Should you be tracing against assumed current AND assumed current flows opposite the source's preferred direction, you ADD the voltage source's voltage.  (double negatives)


IF your battery is ideal, there is no difference between EMF and terminal voltage.

IF your battery is non-ideal, there IS a difference between EMF and terminal voltage, and you MUST model your battery as an ideal voltage source in series with a resistance called the internal resistance.  Draw a dashed line box around this combination for clarity.