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Alternating Current question

2023 · 6 Apr · Shift 2 · Q52
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  5. /2023 · 6 Apr · Shift 2 · Q52

Alternating Current question

2023 · 6 Apr · Shift 2 · Q52

JEE MainPhysicsAlternating CurrentMCQ+4 / −1
A capacitor of capacitance 150.0 μF150.0 ~\mu \mathrm{F}150.0 μF is connected to an alternating source of emf given by E=36sin⁡(120πt)V\mathrm{E}=36 \sin (120 \pi \mathrm{t}) \mathrm{V}E=36sin(120πt)V. The maximum value of current in the circuit is approximately equal to :
  1. A
    12A\frac{1}{\sqrt{2}} A2​1​A
  2. B
    22A2 \sqrt{2} A22​A
  3. C
    2A\sqrt{2} A2​A
  4. D
    2A2 A2A
View written solutionFree

Correct answer: D

  1. Given data
  • Capacitance: C=150.0 μF=150×10−6 FC = 150.0\,\mu\text{F} = 150 \times 10^{-6}\,\text{F}C=150.0μF=150×10−6F
  • Applied emf: E=36sin⁡(120πt) VE = 36\sin(120\pi t)\,\text{V}E=36sin(120πt)V

Comparing with the standard form E=E0sin⁡(ωt),E = E_0 \sin(\omega t),E=E0​sin(ωt), we get:

  • Peak voltage: E0=36 VE_0 = 36\,\text{V}E0​=36V
  • Angular frequency: ω=120π rad/s\omega = 120\pi\,\text{rad/s}ω=120πrad/s
  1. Formula for maximum current in a purely capacitive AC circuit

For a capacitor, I0=ωCE0I_0 = \omega C E_0I0​=ωCE0​

because capacitive reactance is XC=1ωC,X_C = \frac{1}{\omega C},XC​=ωC1​, and hence I0=E0XC=E0ωC.I_0 = \frac{E_0}{X_C} = E_0\omega C.I0​=XC​E0​​=E0​ωC.

  1. Substitute the values

I0=(120π)(150×10−6)(36)I_0 = (120\pi)(150\times 10^{-6})(36)I0​=(120π)(150×10−6)(36)

Now simplify:

150×36=5400150\times 36 = 5400150×36=5400

So, I0=120π×5400×10−6I_0 = 120\pi \times 5400 \times 10^{-6}I0​=120π×5400×10−6

5400×10−6=5.4×10−35400 \times 10^{-6} = 5.4\times 10^{-3}5400×10−6=5.4×10−3

Thus, I0=120π×5.4×10−3I_0 = 120\pi \times 5.4\times 10^{-3}I0​=120π×5.4×10−3

120×5.4×10−3=0.648120 \times 5.4\times 10^{-3} = 0.648120×5.4×10−3=0.648

Therefore, I0=0.648πI_0 = 0.648\piI0​=0.648π

Using π≈3.14\pi \approx 3.14π≈3.14, I0≈0.648×3.14≈2.04 AI_0 \approx 0.648 \times 3.14 \approx 2.04\,\text{A}I0​≈0.648×3.14≈2.04A

  1. Approximate answer

I0≈2 AI_0 \approx 2\,\text{A}I0​≈2A

  1. Option check
  • A: 12 A≈0.707 A\frac{1}{\sqrt{2}}\,\text{A} \approx 0.707\,\text{A}2​1​A≈0.707A
  • B: 22 A≈2.828 A2\sqrt{2}\,\text{A} \approx 2.828\,\text{A}22​A≈2.828A
  • C: 2 A≈1.414 A\sqrt{2}\,\text{A} \approx 1.414\,\text{A}2​A≈1.414A
  • D: 2 A2\,\text{A}2A

So the correct option is D.

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