RL circuit with three resistors

In summary: B: How does the current through the inductor change when the switch is reopened?"After the switch has been reopened for a very long time, how much energy EL is stored in the inductor?"This question is asking for the relation between voltage and current after a time interval has elapsed. This question is asking for the relation between voltage and current after a time interval has elapsed.
  • #1
syhpui2
28
0

Homework Statement



http://i.imgur.com/22jq3.png

22jq3.png


Three identical resistors are connected to a battery, an inductor, and a switch as shown in the figure. (The values of all circuit elements are given below the figure.) The switch has been open for a very long time, and then it is closed at time t = 0.

Part A

Immediately after the switch is closed, the voltage VL across the inductor is
(a) VL = 0 V
(b) VL = 6 V Correct
(c) Neither of the above answers is correct.

Part B

After the switch has been closed for a very long time, how much energy EL is stored in the inductor?
(a) EL = 3.30 × 10-6 J Correct
(b) EL = 5.62 × 10-6 J
(c) EL = 8.63 × 10-6 J
(d) EL = 1.07 × 10-5 J
(e) EL = 1.12 × 10-5 J

Part C
After the switch has been closed for a very long time, a steady current has been established through the inductor. The switch is then reopened. What fraction of this current, fI, remains after a time interval of Δt = 3 μsec has elapsed?
(a) fI = 0.0521
(b) fI = 0.0926
(c) fI = 0.158
(d) fI = 0.201
(e) fI = 0.236 Correct




Homework Equations




KVL, KCL

The Attempt at a Solution



Part A,
can i just say regardless of any situation, VL is equal to Vbattery immdiately after switch is closed?

Part B,
I can't find the current across L. in this case.

Part C,

I am not sure how to start with this question.

Thx
 
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  • #2
You need the relation between voltage and current across the inductor.

ehild
 
  • #3
A: When you first try to push current through an inductor, does it act like a short circuit, an open circuit, or a resistive circuit?

"current across L" is an odd statement, since current is never "across" anything. Current flows THROUGH things due to voltage ACROSS things. This is NOT semantics, it is integral to how electricity works.
 
  • #4
phinds said:
A: When you first try to push current through an inductor, does it act like a short circuit, an open circuit, or a resistive circuit?

"current across L" is an odd statement, since current is never "across" anything. Current flows THROUGH things due to voltage ACROSS things. This is NOT semantics, it is integral to how electricity works.

No current? I think...
 
  • #5
Yes. Your answer to Part A is correct.

ehild
 

1. What is an RL circuit with three resistors?

An RL circuit with three resistors is an electrical circuit that contains three resistors (components that resist the flow of electricity) and an inductor (a device that stores energy in a magnetic field). It is typically used to control the flow of electric current in a circuit.

2. How does an RL circuit with three resistors work?

An RL circuit with three resistors works by passing electric current through the resistors, which causes a voltage drop across each resistor. The inductor, which is made of a coil of wire, creates a magnetic field when current passes through it. The changing magnetic field induces a voltage in the inductor, which opposes the flow of current. This causes the current to decrease over time, making it an example of a "transient" circuit.

3. What is the purpose of using three resistors in an RL circuit?

The three resistors in an RL circuit serve different purposes. The first resistor, known as the "load resistor," controls the amount of current that flows through the circuit. The second resistor, called the "series resistor," limits the flow of current through the inductor. The third resistor, known as the "parallel resistor," helps to dissipate any excess energy stored in the inductor and prevent damage to the circuit.

4. What factors affect the behavior of an RL circuit with three resistors?

The behavior of an RL circuit with three resistors is affected by several factors, including the values of the resistors and inductor, the voltage applied to the circuit, and the time constant (a measure of how quickly the circuit responds to changes in voltage). The position of the resistors in the circuit can also impact its behavior.

5. What are some real-world applications of RL circuits with three resistors?

RL circuits with three resistors are commonly used in electronic devices such as power supplies, amplifiers, and filters. They can also be found in automotive ignition systems, where they help to regulate the flow of current to the spark plugs. Additionally, RL circuits are used in radio frequency identification (RFID) systems, which use inductors to transmit data wirelessly.

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