Q 1 :

A capacitor of capacitance 100 μF is charged to a potential of 12 V and connected to a 6.4 mH inductor to produce oscillations. The maximum current in the circuit would be                     [2024]

  • 3.2 A

     

  • 1.5 A

     

  • 2.0 A

     

  • 1.2 A

     

(2)     

          From energy conservation, 12CV2=12Limax2

          Imax=CLV=100×10-66.4×10-3×12=128=32=1.5A

 



Q 2 :

In an LC oscillator, if values of inductance and capacitance become twice and eight times, respectively, then the resonant frequency of the oscillator becomes 'x' times its initial resonance frequency ω0. The value of 'x' is                      [2023]

  • 14

     

  • 4

     

  • 16

     

  • 116

     

(1)

ω=1LC

ωω0=LC8L·2C=14

ω=ω04



Q 3 :

An oscillating LC circuit consists of a 75 mH inductor and a 1.2μF capacitor. If the maximum charge to the capacitor is 2.7μC, the maximum current in the circuit will be ______ mA.                        [2023]



(9)

Maximum energy stored in capacitor is same as maximum energy stored in inductor.

12Limax2=12Qmax2C

imax=1LCQmax

       =2.7×10-675×10-3×1.2×10-6=9 mA



Q 4 :

A coil has an inductance of 2 H and resistance of 4Ω. A 10 V is applied across the coil. The energy stored in the magnetic field after the current has built up to its equilibrium value will be _________ ×10-2 J.                          [2023]



(625)

I=VR=52 A

E=12LI2=12×2×(52)2

E=625×10-2 J



Q 5 :

Inductance of a coil with 104 turns is 10 mH and it is connected to a dc source of 10 V with internal resistance of 10Ω. The energy density in the inductor when the current reaches (1e) of its maximum value is απ×1e2J/m3. The value of α is ________.       (μ0=4π×10-7Tm/A) .                             [2026]



(20)

L=10×10-3 H

N=104

I0=1010=1 A    (max current)

I=1e

Ed=B22μ0

B=μ0nI

L=μ0n2πR2

Ed=μ0n2I22

=4π×10-7×108×1e22

=20πe2