To find the reverse resistance of the diode, we can use Ohm's law, which is given by:
\[
R = \frac{\Delta V}{\Delta I}
\]
where:
- \( \Delta V \) is the change in voltage,
- \( \Delta I \) is the change in current.
The reverse potential changes from 10 V to 15 V, so:
\[
\Delta V = 15 \, \text{V} - 10 \, \text{V} = 5 \, \text{V}
\]
The reverse current changes from 20 \(\mu\text{A}\) to 40 \(\mu\text{A}\), so:
\[
\Delta I = 40 \, \mu\text{A} - 20 \, \mu\text{A} = 20 \, \mu\text{A} = 20 \times 10^{-6} \, \text{A}
\]
Now substitute the values into the formula for resistance:
\[
R = \frac{5 \, \text{V}}{20 \times 10^{-6} \, \text{A}} = \frac{5}{20 \times 10^{-6}} = 250 \times 10^{3} \, \Omega = 250 \, \text{k}\Omega
\]
Thus, the reverse resistance of the junction diode is \( 250 \, \text{k}\Omega \).