Calculating Inductance in an RL Circuit

In summary, the problem involves an RL circuit with a 9.0 V battery and a 5.5 ohm resistor. The current in the circuit increases from 0 to 0.30 A in 0.17 s when the switch is closed. To find the inductance, we can use the equation I(t) = (V/R) e^(-tR/L), where v = 9, r = 5.5, and t = 0.17. This leaves the inductance as the only unknown variable, which can be solved for using the given values. Once the inductance is known, we can use the equation τ = L/R to find the time constant. Finally,
  • #1
n.hirsch1
14
0

Homework Statement



An RL circuit has a 9.0 V battery and a 5.5 ohm resistor. When the switch is closed, the current in the circuit is observed to increase from 0 to 0.30 A in 0.17 s.
A) What is the inductance?
B) How long after the switch is closed does the current have the value 0.47 A?


Homework Equations


τ = L/R
EMF = L*I / t
I = EMF / R *(1-e^-tR/L)

The Attempt at a Solution


I don't know how to find a time constant, my text doesn't explain it, which makes me think that this question may not even use this equation. I can't get to part B without an answer to part A. By using the second equation I got L = 5.1, but that isn't correct.
 
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  • #2
n.hirsch1 said:

Homework Statement



An RL circuit has a 9.0 V battery and a 5.5 ohm resistor. When the switch is closed, the current in the circuit is observed to increase from 0 to 0.30 A in 0.17 s.
A) What is the inductance?
B) How long after the switch is closed does the current have the value 0.47 A?


Homework Equations


τ = L/R
EMF = L*I / t
I = EMF / R *(1-e^-tR/L)

The Attempt at a Solution


I don't know how to find a time constant, my text doesn't explain it, which makes me think that this question may not even use this equation. I can't get to part B without an answer to part A. By using the second equation I got L = 5.1, but that isn't correct.

are you sure you don't know how?
 
  • #3
No, I don't. Its asking for inductance, I have resistance, I have no idea how to get the time constant.
 
  • #4
n.hirsch1 said:
No, I don't. Its asking for inductance, I have resistance, I have no idea how to get the time constant.

[tex]I(t) = \frac{v}{R} e^{\frac{-tR}{L}}[/tex]
You know the value of current = 300mA at t = .17. v = 9 and r = 5.5. This leaves 1 unknown. Solve for it.
 

1. What is an RL circuit inductance problem?

An RL circuit inductance problem refers to a circuit that contains both a resistor (R) and an inductor (L). These two components interact to create an inductive reactance, which can cause problems in the circuit's performance.

2. How does an inductor affect an RL circuit?

An inductor stores energy in the form of a magnetic field, which resists changes in current flow. In an RL circuit, this can cause a lag in the flow of current, leading to an increase in the overall impedance of the circuit.

3. What is the formula for calculating inductive reactance in an RL circuit?

The formula for calculating inductive reactance is XL = 2πfL, where XL is the inductive reactance, f is the frequency of the current, and L is the inductance of the circuit.

4. How can I solve an RL circuit inductance problem?

To solve an RL circuit inductance problem, you can use Kirchhoff's voltage law and Ohm's law to set up a system of equations. Then, you can use algebra to solve for the unknown variables, such as current or voltage.

5. What are some common applications of RL circuits?

RL circuits are commonly used in electronics, such as in power supplies and motor control circuits. They are also used in telecommunications, where they help to filter out unwanted signals and reduce interference.

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