Applying Kirchoff's Law in an R-L circuit with parallel resistors

AI Thread Summary
In analyzing the R-L circuit with parallel resistors, it is established that for a long-closed switch, the inductor behaves like a wire, making the right resistor effectively irrelevant for current calculations. The current through the inductor before the switch is opened can be calculated using Ohm's Law, I = V/R, where V is the voltage and R is the resistance. The voltage across the right resistor before the switch is opened is also discussed, emphasizing the need to consider the current distribution immediately after the switch is opened. The confusion regarding the timing of the switch's state is clarified, confirming that the current in the right resistor should be evaluated right after the switch is opened. This discussion highlights the importance of accurately applying Kirchhoff's Law in circuit analysis.
amolv06
Messages
45
Reaction score
0
http://img296.imageshack.us/img296/6961/circuithk7.jpg

Assume that the switch has been closed a long time.

1.) Find the current through the inductor before the switch is opened.
2.) Find the voltage in the right resistor before the switch is opened.
3.) Find the current in the right resistor right after the switch is closed.

My question here is how do you treat both resistors? My hunch tells me that the right resistor is irrelevant, and that loop should be treated as superfluous, but I'm not sure. If anyone could answer that question, I would greatly appreciate it. Thanks.
 
Last edited by a moderator:
Physics news on Phys.org
I think 3.) should end in "After the switch is opened".

For a DC current, an inductor is just a wire. This makes the exact value of the right resistor indeed irrelevant.

for 3.) I can't say that the right loop is irrelevant. What happens to the current in the inductor right after you close the switch? where will this current now go?
 
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 then should look like the following?

\frac{V}{R} = I where I is 55/150?
 
Last edited:
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 should be:

I=V/R where I = 55/150?
 
amolv06 said:
Thanks, I completely mistyped that. 3 should read opened rather than closed.

Just to clarify, the answer to #1 should be:

I=V/R where I = 55/150?

Yes, that is the answer
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Trying to understand the logic behind adding vectors with an angle between them'
My initial calculation was to subtract V1 from V2 to show that from the perspective of the second aircraft the first one is -300km/h. So i checked with ChatGPT and it said I cant just subtract them because I have an angle between them. So I dont understand the reasoning of it. Like why should a velocity be dependent on an angle? I was thinking about how it would look like if the planes where parallel to each other, and then how it look like if one is turning away and I dont see it. Since...
Back
Top