What Happens to Current Direction in an RL Circuit When the Switch is Opened?

In summary, the conversation discusses a circuit with a battery, switch, inductor, and three resistors. The switch is initially open and then closed at time t = 0. After being closed for a long time, the switch is opened and the direction of the current in the right hand loop is questioned. The correct answer is counterclockwise. Ampere's law is mentioned as a possible equation to use. The attempt at a solution involves finding the direction of current before and after the switch is opened, with conflicting answers given. Further discussion includes questioning the currents and voltages in the circuit.
  • #1
syhpui2
28
0

Homework Statement



A circuit made with a battery, a switch, an inductor. and three resistors is shown in the figure. To begin with, switch S has been open for a long time. Then at time t = 0 the switch is closed.

http://i.imgur.com/ws5UD.png
ws5UD.png


After being closed for a long time, the switch S is now opened.
What is the direction of the current in the right hand loop containing L, R2 and R3 immediately after the switch is opened?

(a) clockwise
(b) counterclockwise Correct Answer

Homework Equations



Ampere's law?

The Attempt at a Solution



I am not sure how do I ind the direction of current if switch is opened? Should be no current?

Thx
 
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  • #2
Before the switch is opened, what currents are flowing and in what directions?
 
  • #3
gneill said:
Before the switch is opened, what currents are flowing and in what directions?

There are current on r2,r3 and inductor and it is clockwise...
 
  • #4
syhpui2 said:
There are current on r2,r3 and inductor and it is clockwise...

No, that's not right. Yes, there is current through the inductor, but what is that current and what is the voltage across the inductor? What about R1?
 
  • #5




The direction of current in a circuit is determined by the flow of electrons. When the switch is closed, the battery creates a potential difference, causing electrons to flow in a specific direction. In an RL circuit, the inductor also plays a role in determining the direction of current.

When the switch is first closed, the current will flow in a counterclockwise direction in the right hand loop containing L, R2, and R3. This is because the inductor resists changes in current, so it initially acts as a barrier to the flow of current.

When the switch is opened, the flow of current is disrupted and the inductor will try to maintain the current flow. This means that the current will continue to flow in the same direction, counterclockwise, in the right hand loop.

Therefore, the correct answer is (b) counterclockwise. This can also be confirmed using Ampere's law, which states that the direction of the magnetic field created by the current is always perpendicular to the direction of the current flow. So if the current is flowing counterclockwise, the magnetic field will be directed out of the page, as shown in the figure.
 

FAQ: What Happens to Current Direction in an RL Circuit When the Switch is Opened?

What is the direction of current in an RL circuit?

In an RL (resistor-inductor) circuit, the current flows in the direction determined by the polarity of the voltage source. The current will flow from the positive terminal of the voltage source, through the resistor, and into the inductor. It will then flow out of the inductor and back to the negative terminal of the voltage source.

Does the current direction change in an RL circuit?

Yes, the direction of current in an RL circuit can change over time. This is due to the inductor's property of opposing changes in current. When the voltage source is first connected, the current will initially increase in one direction. As the current increases, the inductor builds up a magnetic field, which then resists the change in current. This causes the current to decrease in the original direction and start increasing in the opposite direction. This process continues, resulting in a back-and-forth flow of current in the circuit.

How does the current direction affect the behavior of an RL circuit?

The direction of current in an RL circuit plays a crucial role in the circuit's overall behavior. When the current is increasing in one direction, the inductor stores energy in its magnetic field. When the current is decreasing and flowing in the opposite direction, the inductor releases this stored energy. This back-and-forth flow of energy allows the circuit to maintain a constant current, even when the voltage source is removed.

Can the current direction in an RL circuit be reversed?

Yes, the current direction in an RL circuit can be reversed by changing the polarity of the voltage source. When the polarity is reversed, the current will also reverse direction, flowing in the opposite direction through the circuit. This change in current direction will also cause changes in the behavior of the circuit, such as the rate at which the inductor's magnetic field builds up or dissipates.

How can the current direction in an RL circuit be determined?

The current direction in an RL circuit can be determined by using the "right-hand rule" for current flow. With your right hand, point your thumb in the direction of current flow. Then, curl your fingers around the inductor in the direction of the magnetic field. Your fingers should point towards the positive terminal of the voltage source, indicating the direction of current flow. Alternatively, you can use Kirchhoff's voltage law to determine the direction of current by analyzing the voltage drops across each component in the circuit.

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