Current in Inductor: Calculate Voltage at 7A

In summary, the conversation discusses finding the voltage across an inductor at the instant when the current decreases to 7 A with a time constant of 3 seconds. The solution involves using the equation for a discharging inductor in an RL circuit and taking into account the internal resistance. The final answer depends on the value of the resistance in the circuit.
  • #1
Angello90
65
0

Homework Statement


If the current in the inductor 10mH decreases exponentially from its
initial value of 14 A with a time constant of 3 seconds, what is the voltage
across the inductor at the instant when the current reaches 7 A?


Homework Equations


V(t)=L di/dt


The Attempt at a Solution


di = 7, dt=3
thus
V=(10e-3)(7/3)=0.0233v

Am I correct? Seems to be too simple for me
 
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  • #2
Angello90 said:

Homework Statement


If the current in the inductor 10mH decreases exponentially from its
initial value of 14 A with a time constant of 3 seconds, what is the voltage
across the inductor at the instant when the current reaches 7 A?

Homework Equations


V(t)=L di/dt

The Attempt at a Solution


di = 7, dt=3
thus
V=(10e-3)(7/3)=0.0233v

Am I correct? Seems to be too simple for me
you have to use the equation for a discharging inductor in an RL circuit.
[tex]V=IR[/tex]
[tex]V_{inductor} - V_{resistor} = 0[/tex]
[tex]L\frac{di}{dt} = IR[/tex]
[tex] \frac{R}{L}dt = \frac{di}{i}[/tex]
[tex] \frac{Rt}{L}= ln(i) + c_1[/tex]
[tex] i(t) = c_2e^{\frac{Rt}{L}}[/tex]
[tex]c_2[/tex] is the initial current (which is given)
 
  • #3
but there is no resistor in the circuit
 
  • #4
Angello90 said:
but there is no resistor in the circuit
We know that the time constant is equal to:
[tex]\frac{L}{R}[/tex[
Since the inductor has a time constant other than infinity, we know that there is a resistance. If resistance was zero, the time constant would be infinity, and the inductor would never lose current (i.e. it would never lose energy) since there would be no resistive losses.Since we know L and Timeconsant, we can solve for resistance if you wanted to know it.
 
  • #5
Ok now I get it. It's all about internal resistance right?

Thanks a lot xcvxcvc
 

1. What is an inductor?

An inductor is an electronic component that stores energy in the form of a magnetic field. It is typically made of a coiled wire and is used in circuits to regulate current flow and create voltage changes.

2. How does current affect the voltage in an inductor?

According to Ohm's law, the voltage in an inductor is directly proportional to the rate of change of current. In other words, the faster the current changes, the higher the voltage will be.

3. How do you calculate the voltage in an inductor at a specific current?

To calculate the voltage in an inductor at a specific current, you can use the equation V = L di/dt, where V is the voltage, L is the inductance, and di/dt is the change in current over time.

4. What is the unit of measurement for inductance?

Inductance is measured in units called henries (H), named after the scientist Joseph Henry who first discovered the phenomenon of inductance.

5. How does the voltage at 7A compare to the voltage at 10A in an inductor?

The voltage at 7A will be lower than the voltage at 10A in an inductor. This is because the rate of change of current at 7A is slower than at 10A, resulting in a lower voltage according to the equation V = L di/dt.

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