The `V-I` characteristic of a silicon diode is shown in the Fig. Calculate the resistance of the diode at
(a) `I_(D) = 15 mA` and
(b) `V_(D) = -10 V`.
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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 = 10mA,V = 0.7 V`
`r_(fb) =Delta V //Delta I = 0.1 V //10 mA = 10 Omega`
(b) From the curve at
`V = -10 V, I = -1 mu A`
Therefore, `r_(rb) =10 V//1 muA = 1.0 xx 10^(7) Omega`.