wat is static and dynamic resistance ?

Static Resistance is basically the DC resistance offered by a pn junction diode and originates when it is connected in a DC circuit. It is the resistance offered by the diode to the flow of DC current.

Mathematically, it is given as the ratio of the DC voltage across the terminals of the diode to the DC current flowing through it.

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Dynamic Resistance is the AC resistance offered by a pn junction diode and originates when it is connected in an AC circuit. It is the resistance offered by the diode to the flow of AC current.

Mathematically, it  given as the ratio of the change in AC voltage across the terminals of the diode to the resulting change in AC current flowing through it.