MEDIUM
JEE Main/Advance
IMPORTANT
Earn 100

For an RLC circuit driven with a voltage of amplitude Vm and frequency ω0=1LC the current exhibits resonance. The quality factor Q is given by: 

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Important Questions on Alternating Current

MEDIUM
JEE Main/Advance
IMPORTANT
In an A.C. circuit, the instantaneous e.m.f. and current are given by, E=100sin30t,I=20sin30t-π4. In one cycle of A.C., the average power consumed by the circuit (in watt) and the watt-less current (in ampere) are, respectively:
EASY
JEE Main/Advance
IMPORTANT

Hysteresis loops for two magnetic materials A and  B are given below :

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These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use :

MEDIUM
JEE Main/Advance
IMPORTANT

An LCR circuit is equivalent to a damped pendulum. In an LCR circuit the capacitor is charged to Q0 and then connected to the L and R as shown below:

 

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If a student plots graphs of the square of maximum charge (Q2Max) on the capacitor with time (t) for two different values L1 and L2(L1>L2) of L then which of the following represents this graph correctly? (Plots are schematic and not drawn to scale)

MEDIUM
JEE Main/Advance
IMPORTANT
A current of 4 A flows in a coil when connected to a 12 V d.c. source. If the same coil is connected to a 12 V, 50 rad s-1, AC source, a current of 2.4 A flows in the circuit. Determine the inductance of the coil. Also, find the power developed in the circuit if a 2500 μF condenser is connected in series with coil.
HARD
JEE Main/Advance
IMPORTANT
A box P and a coil Q are connected in series with an AC source of variable frequency. The EMF of source is constant at 10 V. Box P contains a capacitance of 1 μF in series with a resistance of 32 Ω. Coil Q has a self inductance 4.9 mH and a resistance of 68 Ω. The frequency is adjusted so that the maximum current flows in P and Q. Find the impedance of P and Q at this frequency. Also find the voltage across P and Q, respectively.
MEDIUM
JEE Main/Advance
IMPORTANT

In a series LCR circuit with an ac source of 50 V, R=300Ω, frequency v=50π Hz. The average electric field energy stored in the capacitor and average magnetic energy stored in the coil are 25 mJ and 5 mJ, respectively. The RMS current in the circuit is 0.10 A. Then find:

(a) Capacitance (c) of capacitor 

(b) Inductance (L) of inductor.

(c) The sum of rms potential difference across the three elements.

HARD
JEE Main/Advance
IMPORTANT
An inductor 20 × 103 Henry, a capacitor 100 μF and a resistor 50 Ω are connected in series across a source of EMF V=10 Vsin314t. Find the energy dissipated in the circuit in 20 min. If resistance is removed from the circuit and the value of inductance is doubled, then find the variation of current with time (t in second) in the new circuit.
EASY
JEE Main/Advance
IMPORTANT
The electric current in an AC circuit is given by i=i0sinωt. What is the time taken by the current to change from its maximum value to the rms value?