The switch in the circuit has been open for a long time. Immediately after it is

Question

The switch in the circuit has been open for a long time. Immediately after it is closed, what is the CURRENT through THE INDUCTOR?

E/R1
0
E/(R1+R2)
E/L
E/R2
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Immediately after the switch has been closed, what can you say about the current in R1?

It is the same as the current in R2, and they are both equal to zero.
It is zero, and not the same as the current through R2
It is greater than the current through R2
It is the same as the current in R2, but greater than zero.
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What is the correct loop rule for a loop that goes through the battery, the inductor, and Resistor 1?

+E ? ?VL ? I1 R1 = 0
+E ? ?VL ? I1 R1 ? I2 R2 = 0
+E ? I1 R1 = 0
+E ? ?VL + I1 R1 = 0
+E ? L ? I1 R1 = 0
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Immediately after the switch is closed, what is the VOLTAGE across the INDUCTOR?
I L
E?I1 R1
E?I2 R2
E
0
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Explanation / Answer

You need to understand the behavior of an inductance L. Initially the current through an inductor is zero, and the current increases with time as voltage across the inductor/L; that is dI/dt = V/L.
A. The inductance initially passes zero current, so I = 10/20 = 0.5 A.
B. In steady state dI/dt = 0 so the voltage across the inductor = 0. Thus you can treat the inductor as a short circuit, and I = 10/(20||20) = 10/10 = 1 A.

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