The lightbulb has a different dynamic resistance depending on whether the voltage is increasing or decreasing....

The lightbulb has a different dynamic resistance depending on whether the voltage is increasing or decreasing. Explain why the dynamic resistance is different under these two conditions.

Expert Solution

The lightbulb uses materials that does not obey ohm's law in simple fashion i.e. some materials possess resistance which can change under different circumstances.

A material can be characterized electrically by measuring the current (I) that flows through the material when an electric potential difference (V) is applied across it. This information is most readily displayed in an IV curve (called the characteristic curve) which is a graph of the resulting current flow versus potential difference. A material is said to be Ohmic, or to obey Ohm's law, if the ratio of the voltage V to the current I is a constant. This constant is the resistance R and has the units of volts / amperes, or ohms.

Graphically, an ohmic device is characterized by a linear IV curve. Most metals are ohmic if the temperature is not allowed to vary appreciably. For materials that are non ohmic, the current - voltage relation can be a complicated function of the voltage. With some nonlinear IV curves, the definition of resistance given above is of little use in allowing a determination of the current for given potential difference. A more useful quantity is the dynamic resistance

         R =  delta V / delta I

which is defined by the small change in current (delta I) resulting from a small change in the potential difference (delta V). Graphically, this is the reciprocal of the slope of a tangent line drawn to the characteristic curve.

Here delta V decides the resistance not the V. Dynamic resistance can be positive or negative depending on delta V.

genius_generous answered 5 months ago

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