Answer:
The current of the circuit at t = 0 is equal to 0.
If we take the limit as t approaches infinity, the current is equal to ε/R or V/R.
General Formulas and Concepts:
<u>Calculus</u>
Differentiation
- Derivatives
- Derivative Notation
Derivative Property [Multiplied Constant]:

Derivative Property [Addition/Subtraction]:

Derivative Rule [Basic Power Rule]:
- f(x) = cxⁿ
- f’(x) = c·nxⁿ⁻¹
Slope Fields
Integration
Integration Rule [Reverse Power Rule]:

Integration Rule [Fundamental Theorem of Calculus 1]:

Integration Property [Multiplied Constant]:

Integration Method: U-Substitution
<u>Electricity</u>
Ohm's Law: V = IR
- <em>V</em> is voltage (in Volts)
- <em>I</em> is current (in Amps)
- <em>R</em> is resistance (in Ohms)
<u>Circuits</u>
- Circuit Symbols
- Kirchhoff's Laws (Loop and Junction Rule)
- Inductors
Step-by-step explanation:
*Note:
In the given equation, our variable of differentiation is <em>x</em>. I will rewrite this as current <em>I</em> for physics notation purposes.
<u>Step 1: Define</u>
<em>Identify given.</em>

[Assuming switch <em>S</em> is closed] Recall that an inductor is used in a circuit to <em>resist</em> change. After a long period of time, when it hits steady-state equilibrium, we expect to see the inductor act like a wire.
<u>Step 2: Find Current Expression Pt. 1</u>
- [Kirchhoff's Law] Rewrite expression:

- Rewrite expression by dividing <em>R</em> on both sides:

<u>Step 3: Find Current Expression Pt. 2</u>
<em>Identify variables for u-substitution.</em>
- Set <em>u</em>:

- [<em>u</em>] Differentiation [Derivative Rules and Properties]:

<u>Step 4: Find Current Expression Pt. 3</u>
- [Kirchhoff's Law] Apply U-Substitution:

- [Kirchhoff's Law] Apply Separation of Variables:

Recall that our initial condition is when t = 0, denoted as <em>u₀</em>, and we go to whatever position <em>u</em> we are trying to find. Also recall that time <em>t</em> always ranges from <em>t</em> = 0 (time can't be negative) and to whatever <em>t</em> we are trying to find.
- [Kirchhoff's Law] Integrate both sides:

- [Kirchhoff's Law] Rewrite [Integration Property]:

- [1st Integral] Apply Logarithmic Integration:

- [2nd Integral] Apply Integration Rule [Reverse Power Rule]:

- Apply Integration Rule [Fundamental Theorem of Calculus 1]:

- Apply e to both sides:

- Simplify:

- Rewrite:

Recall that our initial condition <em>u₀</em> (derived from Ohm's Law) contains only the voltage across resistor <em>R</em>, where voltage is supplied by the given battery. This is because the current is stopped once it reaches the inductor in the circuit since it <em>resists</em> change.
- Back-Substitute in <em>u </em>and <em>u₀</em>:

- Solve for <em>I</em>:

<u>Step 5: Solve</u>
If we are trying to find the strength of the electrical current <em>I</em> at <em>t</em> = 0, we simply substitute <em>t</em> = 0 into our current function:

If we are taking the limit as <em>t</em> approaches infinity of the current function <em>I(t)</em>, we are simply just trying to find the current <em>after a long period of time</em>, which then would just be steady-state equilibrium:

∴ we have found the current <em>I</em> at <em>t</em> = 0 and the current <em>I</em> after a long period of time and proved that an inductor resists current running through it in the beginning and acts like a wire when in electrical equilibrium.
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Topic: AP Physics C - EMAG
Unit: Induction