Explain the differences and similarities between resistivity and resistance. Def

Question

Explain the differences and similarities between resistivity and resistance. Define current and explain which charge carriers are mobile in a conventional conductor (metal). How does the temperature affect the conductivity of a metal? A semiconductor? What causes a current to flow? What can slow it down? On the diagram below indicate how you would measure the current through and the voltage across the lightbulb. Let V indicate the multimeter DC voltage mode and A indicate it in DC current mode. Clearly indicate the position of the leads in each scenario. In a basic RC circuit indicate on the graph how the current would change in time as an initially fully charged capacitor is discharged over a resistance "R". Label the axis. Indicate how this curve would change if the resistance "R" were doubled without changing the capacitance value.

Explanation / Answer

The above questions have been answered correctly. Below is the answer for [f]

f]

The current in an RC circuit is given by: I = Ioe -t/RC

So, as time passes by, the current in the circuit decreases exponentially as the voltage drop across the capacitor rises exponentially. So, the curve for the current will be an exponentially decaying function with current on y axis and time on x axis. At t = 0s, I = Io .

If R' = 2R

then I = Ioe-t/2RC

re-arranging this gives, t' = - R'C ln(I/Io) = 2RC ln(Io/I)

So, the time taken to reach from I to Io to I is more if R is increased to 2R. Therefore, the graph will be less steep than the first graph.

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