Graphing current vs. time in an RL circut

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SUMMARY

This discussion focuses on graphing current (I(1) and I(2)) versus time in an RL circuit, emphasizing the behavior of inductors in response to a voltage source. The key equations involved include Ohm's Law (V = IR) and the back EMF equation (Back EMF = -L * dI/dt). It is established that the current in an ideal inductor grows gradually due to Lenz's law, opposing abrupt changes, and that the voltage across the inductor is the negative of the back EMF. The relationship between current and time is not purely exponential due to the influence of the back EMF.

PREREQUISITES
  • Understanding of RL circuit dynamics
  • Familiarity with Lenz's law
  • Knowledge of differential equations related to electrical circuits
  • Basic grasp of graphing functions in physics
NEXT STEPS
  • Study the transient response of RL circuits using differential equations
  • Learn how to graph current and voltage in RL circuits over time
  • Explore the effects of resistance in parallel with inductors
  • Investigate practical applications of inductors in electronic circuits
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Electrical engineering students, educators teaching circuit theory, and hobbyists interested in understanding RL circuit behavior and graphing techniques.

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Homework Statement



Graph I(1) and I(2) vs. time. See attachment for illustration.

Homework Equations



V = IR
Back EMF = -L * dI/dt

The Attempt at a Solution



I realize that an inductor is essentially the opposite of a capacitor when it comes to current and voltage: that is, the current starts small and grows with an exponential curve until it plateaus while voltage starts large and drops to nearly nothing. However, I'm not sure how to treat this in parallel with a resistor. Assuming an ideal inductor with no resistance, it should carry a lot of current at the start since the R(L) of the equation of the voltage drop over the inductor V(L) = I(L) * R(L) will be close to zero...but I know this can't be the case!
 

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The current was zero before connecting the voltage source to the coil. You know Lenz's law: The back EMF induced in the coil opposes the change caused by switching on the the battery. The back EMF prevents any abrupt change, the current will grow gradually, not necessarily in an exponential way.

The voltage across the inductor is negative of the back emf:

U = L dI/dt

U is given and constant if it is an ideal voltage source. It does not matter whether you connect a resistor parallel with the coil or not. You can determine the rate of change of I through the coil. This current was zero before the voltage source was switched on. How does the current change with time?

ehild
 

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