Alternating Current – JEE Main Previous Year Questions with Solutions
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Q. In a series LCR circuit R = $200 \Omega$ and the voltage and the frequency of the main supply is 220 V and 50 Hz respectively. On taking out the capacitance from the circuit the current lages behind the voltage by $30^{\circ}$. On taking out the inductor from the circuit the current leads the voltage by $30^{\circ}$. The power dissipated in the LCR circuit is : (1) 242 W (2) 305 W (3) 210 W (4) Zero W [AIEEE – 2010]

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Sol. (1)

Q. A fully charged capacitor C with intial charge $\mathrm{q}_{0}$ is connected to a coil of self inductance L at t = 0. The time at which the energy is stored equally between the electric and the magnetic fields is :- (1) $2 \pi \sqrt{\mathrm{LC}}$ (2) $\sqrt{1 C}$ (3) $\pi \sqrt{\mathrm{LC}}$ (4) $\frac{\pi}{4} \sqrt{\mathrm{LC}}$ [AIEEE – 2011]

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Sol. (4)

Q. In an LCR circuit as shown below both switches are open initially. Now switch S1 is closed, $\mathrm{S}_{2}$ kept open, (q is charge on the capacitor and $\tau=\mathrm{RC}$ is Capacitive time constant). Which of the following statement is correct? (1) Work done by the battery is half of the energy dissipated in the resistor (2) At t $=\tau, q=C \sqrt{/ 2}$ (3) At $\mathrm{t}=2 \pi, \mathrm{q}=\mathrm{CV}\left(1-\mathrm{e}^{-2}\right)$ (4) At $\mathrm{t}=\frac{\tau}{2}, \mathrm{q}=\mathrm{CV}\left(1-\mathrm{e}^{-1}\right)$ [JEE Main-2013]

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Sol. (3)

Q. An LCR circuit is equivalent to a damped pendulum. In an LCR circuit the capacitor is charged to $\mathrm{Q}_{0}$ and then connected to the L and R as shown below. If a student plots graphs of the square of maximum charge on the capacitor with time (t) for two different values $\mathrm{L}_{1}$ and $\mathrm{L}_{2}\left(\mathrm{L}_{1}>\mathrm{L}_{2}\right)$ of L then which of the following represents this graph correctly ? (plots are schematic and not drawn to scale) [JEE Main-2015]

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Sol. (3) As damping is happening its amplitude would vary as The oscillations decay exponentially and will be proportional to $\mathrm{e}^{-\gamma t}$ where $\gamma$ depends inversely on L. So as inductance increases decay becomes slower  for

Q. An arc lamp requires a direct current of 10A at 80V to function. If it is connected to a 220V (rms), 50 Hz AC supply, the series inductor needed for it to work is close to :- (1) 0.065 H (2) 80 H (3) 0.08 H (4) 0.044 H [JEE Main-2016]

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Sol. (1) As damping is happening its amplitude would vary as The oscillations decay exponentially and will be proportional to $\mathrm{e}^{-\gamma t}$ where $\gamma$ depends inversely on L. So as inductance increases decay becomes slower  for

Q. For an RLC circuit driven with voltage of amplitude $\mathrm{v}_{\mathrm{m}}$ and frequency $\mathrm{w}_{0}=\frac{1}{\sqrt{\mathrm{LC}}}$ the current exhibits resonance. The quality factor, Q is given by : (1) $\frac{\omega_{0} \mathrm{R}}{\mathrm{L}}$ ( 2)$\frac{\mathrm{R}}{\left(\omega_{0} \mathrm{C}\right)}$ (3) $\frac{\mathrm{CR}}{\omega_{0}}$ (4) $\frac{\omega_{0} \mathrm{L}}{\mathrm{R}}$ [JEE Main-2018]

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Sol. (4) Quality factor $=\frac{\omega_{0} \mathrm{L}}{\mathrm{R}}$

Q. In an a. c. circuit, the instantaneous e.m.f. and current are given by e = 100 sin 30 t i = 20 sin $\left(30 t-\frac{\pi}{4}\right)$ In one cycle of a.c., the average power consumed by the circuit and the wattless current are, respectively. (1) $\frac{1000}{\sqrt{2}}, 10$ (2) $\frac{50}{\sqrt{2}}, 0$ (3) 50, 0 (4) 50, 10 [JEE Main-2018]

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Sol. (1)

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Comments
  • August 6, 2021 at 11:11 am

    Sir Update bhi krdo PYQS 2020 aur 21 ke plz

    4
  • July 11, 2021 at 10:40 pm

    Keep some more interesting questions along with these…

    1
  • April 30, 2021 at 7:36 pm

    thank you

    1
  • sym
    April 26, 2021 at 12:26 pm

    gd questions

    1
  • January 22, 2021 at 11:23 am

    Thank you

    6
  • December 9, 2020 at 6:25 pm

    Plz add more

    4
  • October 29, 2020 at 1:53 pm

    Thanks Buddy. Whatever question are there……They are quality based. Easy, Medium, Hard sab h. Thanks mate.

    3
  • October 20, 2020 at 5:24 pm

    Nice questions . Thanks for help.

    11
  • September 17, 2020 at 11:04 am

    ques quantity was quite less

    7
  • August 31, 2020 at 7:34 am

    It would be nice if you add 2019&20 questions

    17
    • October 10, 2020 at 12:58 pm

      Aur que nhi h kya sir… I effective se related

      2
  • August 29, 2020 at 7:01 pm

    Arey bhenchod. Tu bhi previous year questions dekh ke exam dene jayega

    4
  • August 27, 2020 at 7:48 pm

    Maa chudi padi hai yaha par

    2
  • August 27, 2020 at 10:20 am

    Thanks for the help.

    0
  • July 4, 2020 at 7:16 pm

    Good things

    0
  • June 8, 2020 at 3:44 pm

    Please make sure that the mathematical terms are correct and please correct the overlapings. Other than this all is well. THANK YOU

    0
  • Ved
    May 29, 2020 at 3:00 pm

    Bcdbhfbf

    0
  • sam
    December 25, 2019 at 8:47 pm

    was really interesting

    21