The V-I characteristic of a silicon diode is shown in the figure . Calculate the resistance of the diode at (a) `I_(D) = 15 mA` and (b) `V_(D) = -10 V `

Explanation

Considering the diode characteristics as a straight line between `I = 10 mA` to I = 20 mA passing through the origin , we can calculate the resistance using Ohm.s law .
a. From the curve , at I = 20 mA , V = 0.8 V , I = 10 mA , V = 0.7 V
`r_(fb) = (DeltaV)/(DeltaI) = (0.1)/(10) = 10 Omega`
b. From the curve at `V = -10V , I = -1 mu A`
`therefore r_(fb) = (10)/(1 mu) = 1.0 xx 10^(7) Omega`