Here is my question: While studying a coil of unknown inductance and internal re

Question

Here is my question:

While studying a coil of unknown inductance and internal resistance, you connect it in series with a 25.0 V battery and a 1.60 Times 102 Ohm resistor. You then place an oscilloscope across one of these circuit elements and use the oscilloscope to measure the voltage across the circuit element as a function of time. The result is shown in the figure. Across which circuit element (coil or resistor) is the oscilloscope connected? Find the inductance of the coil. In instead, the power supply was 20 V, what is the internal resistance of the coil?

Explanation / Answer

a) as in the starting phase of the graph we can notice that V is directly proportional to i, so oscilloscope connect across resistor.

b) voltage across R

Vr= Vo(1-1/e) = 0.63* 25= 16 V

time corresponding to this voltage, t= 0.5 ms

T= L/R

L= TR= 0.5*0.001* 160= 80 *10^-3 H

c) As we can see from graph, as time t approaches infinity, V_r approaches 25 V , therefore we can conclude that there is no voltage drop across the inductor. So, its internal resistance is Zero.

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