Ohm's law is applicable to resistors only. in case of devices such as diodes, transistors, fets, etc., the way they behave on application of a voltage across them is vastly different from how resistors behave (v = ir)' moreover, their behavior is often described by much more complicated equations than v = ir. the dc load line method is one of the ways in electronics to solve problems graphically and, therefore, avoid dealing with seemingly nasty and intractable equations.
This note explains the concept and working of p-n junction diode. the p-n junction is a versatile element, which can be used as a rectifier, as an isolation structure and as a voltage-dependent capacitor.