Answer
$\frac{R_{reverse\;bias}}{R_{forward\;bias}}\approx 20$.
Work Step by Step
A pn junction diode does not obey Ohm’s Law, so “resistance” cannot be defined in the same way that it is for resistors. Instead, for a rough measure of resistance, let us consider the voltage that is required to drive an appreciable current through the device.
See Figure 29–30. We see that about 0.6 V is required to move a significant current through the diode when it is connected in forward bias. On the other hand, a much larger voltage, about 12 V, is required to move a significant current through the diode when it is connected in reverse bias.
In summary, to push the same current, approximately 20 times the voltage is require d in the reverse bias configuration, compared to the voltage required in the forward bias configuration.
One may say that the reverse bias resistance is approximately 20 times larger than the forward bias resistance.
