Electric Circuit Analysis of this First Order R-L Circuit

• Engineering
• Xiao Xiao
In summary, the equation states that the inductance will oppose a change in current, which is what you calculated.
Xiao Xiao
Homework Statement
Finding the current at (a) the instant just before the switch opens (b) the instant just after the switch opens.
Relevant Equations
iL before switch open is i+(0) and iL after the switch opens is i-(0), and i(0)=i+(0)=i-(0) so both have the same value?

Is that really a relevant equation ?

Or just a wild guess.

Please post a realistic attempt at solution, so we can help (PF guidelines forbid us unless...)

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BvU said:
Is that really a relevant equation ?

Or just a wild guess.

Please post a realistic attempt at solution, so we can help (PF guidelines forbid us unless...)

##\ ##
It isn't exactly a related equation but I couldn't leave it empty so I put it there, i have attempted a solution on my own, but my question is just if the current at the instant before the switch opens=the current at the instant right after the switch opens. I just want to know if that's correct or not because it's relevant if I want to continue solving the rest of the question with my solution.

BvU said:
Is that really a relevant equation ?

Or just a wild guess.

Please post a realistic attempt at solution, so we can help (PF guidelines forbid us unless...)

##\ ##
Okay, my professor's lecture was very confusing and didn't properly explain initial conditions, but now I used outside sources to study and my confusion about the question is cleared so I'll delete this in a bit.
Edit: I guess deleting questions doesn't work.

Xiao Xiao said:
It isn't exactly a related equation but I couldn't leave it empty so I put it there, i have attempted a solution on my own, but my question is just if the current at the instant before the switch opens=the current at the instant right after the switch opens. I just want to know if that's correct or not because it's relevant if I want to continue solving the rest of the question with my solution.
You have picked up the essential part of this exercise: the inductance will behave in such a way that a change in current is counter-acted, according to the relationship $$V = L{di\over dt}$$so: bravo, well done !

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Xiao Xiao

1. What is an R-L circuit?

An R-L circuit is a type of electrical circuit that contains both a resistor (R) and an inductor (L). The resistor is a passive element that resists the flow of current, while the inductor is an active element that stores energy in the form of a magnetic field.

2. What is the purpose of analyzing a first-order R-L circuit?

The purpose of analyzing a first-order R-L circuit is to understand how the circuit behaves and how the current and voltage change over time. This can help in designing and troubleshooting electrical systems.

3. How do you calculate the time constant of a first-order R-L circuit?

The time constant (τ) of a first-order R-L circuit can be calculated by dividing the inductance (L) by the resistance (R). This value represents the time it takes for the current to reach 63.2% of its final value in an initially uncharged circuit.

4. What is the relationship between the time constant and the behavior of the circuit?

The time constant is directly related to the behavior of the circuit. A smaller time constant means that the current will rise and reach its maximum value more quickly, while a larger time constant means that the current will take longer to reach its maximum value.

5. How do you analyze the voltage and current in a first-order R-L circuit?

To analyze the voltage and current in a first-order R-L circuit, you can use Kirchhoff's laws and Ohm's law. By applying these laws and using the calculated time constant, you can determine the behavior of the circuit and the values of voltage and current at any given time.

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