Question

• What does it mean for two variables, such as current and potential, to have a linear relationship to each other? Describe two devices— incandescent lamps and diodes— in which current and potential do not follow Ohm’s Law. Why are these two devices exceptions? Use Kirchhoff’s loop rule for potentials and junction rule for currents to describe how a single battery in a car can be used to power multiple electrical devices.

Answer 1

linear relationship is a relationship of direct proportionality that, when plotted on a graph, traces a straight line.

Circuits or components that obey the relation V = IR are known as ohmic and have current-voltage plots that are linear and pass through the origin. In a true ohmic device, the same value of resistance will be calculated from R = V/I regardless of the value of the applied voltage V. That is, the ratio of V/I is constant, and when current is plotted as a function of voltage the curve is linear (a straight line).


Incandescent lamps -
The filament of an incandescent light bulb changes resistance significantly with temperature and therefore, the current through it increases at a slower rate than the increases in potential Difference and thus if forms a non linear Graph line and do not follow Ohm's Law.

Diodes -
In a p-n Junction Diode, a depletion zone forms around the junction (the join) between the two materials. This zone controls the behaviour of the diode. When forward biased - the current first rises slowly as voltage increases and then much rapidly. It is not proportional to the applied voltage across its terminals and does not follow Linear relatonship.

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