Voltage in a circuit with variable resistance and diode in series?
The forward voltage drop of a silicon diode is only approximately 0.7 V. The current through a diode depends exponentially on the voltage across it (i.e. the current is a very strong function of voltage). This means the voltage is a weak function of current, so for currents that you are likely to encounter when the diode is conducting (maybe tens of mA, depending on the application), the forward voltage of the diode typically doesn't deviate much from a fixed value (about 0.7 V). So clearly diodes are different from resistors in this respect.
The constant forward voltage drop approximation is equivalent to the I-V relation of the diode being approximated by I = 0 for V &lt; 0.7 V, and I = ∞ for V &gt; 0.7 V. This means that as long as the diode is &quot;turned on&quot; (its voltage is about 0.7 V), its current could be anything positive depending on the circuit the diode is connected to: in this case the battery and the resistor.