LC Oscillations

IMPORTANT

LC Oscillations: Overview

This topic covers concepts such as L-C Oscillator Circuit, Comparison of L-C Oscillations with Spring Block Oscillations, Frequency of L-C Oscillator Circuit, Comparison between Self Inductance and Inertia, Energy in L-C Oscillator, etc.

Important Questions on LC Oscillations

HARD
IMPORTANT

A circuit consists of a coil with inductance L$L$ and an uncharged capacitor of capacitance C. The coil is in a constant uniform magnetic field such that the flux through the coil is ϕ. At time t=0, the magnetic field was abruptly switched off. Let ω0=1/LC and ignore the resistance of the circuit. Then,

MEDIUM
IMPORTANT

Why is self induction called inertia of electricity?

EASY
IMPORTANT

The self inductance of a long solenoid cannot be increased by

(a) increasing its area of cross section

(b) increasing its length

(c) changing the medium with greater permeability

(d) increasing the number of turns in it

(e) increasing the current through it

EASY
IMPORTANT

The current through a coil of self-inductance L=2mH is given by i=t2e-t at time t. How long it will take to make the emf zero?

EASY
IMPORTANT

When current in coil changes from 5 A to 2 A in 0.1 s, an average of 50 V is produced. The self-inductance in HenryH of the coil is n3. Write the value of n.

EASY
IMPORTANT

A 60μF capacitor is charged to 100 volts. This charged capacitor is connected across a 1.5mH coil, so that LC oscillations occur. The maximum current in the coil is:-

MEDIUM
IMPORTANT

In an LC circuit shown in figure, C=2 F and L=2 H. At time t=0, charge on the capacitor is 3 coulomb and it is decreasing with rate of 4 C s-1. Then choose the correct statement.

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EASY
IMPORTANT

The natural frequency of the circuit is (in rad s-1),

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HARD
IMPORTANT

In an LC oscillator circuit L = 10 mH, C = 40µF. If initially at t = 0 the capacitor is fully charged with 4µC then find the current in the circuit when the capacitor and inductor share equal energies. 

HARD
IMPORTANT

The diagram shows a capacitor C and a resistor R connected in series to an AC source, V1 and V2 are voltmeters and A is an ammeter. Consider now the following statements :

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(I) Readings in A and V1 are always in phase

(II) Readings in A and V2 are always in phase

(III) Reading in V1 is ahead with reading in V2

Which of these statements are is correct : 

EASY
IMPORTANT

The switch in the circuit pictured is in position a for a long time. At t = 0 the switch is moved from a to b. The current through the inductor will reach its first maximum after moving the switch in a time : -

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EASY
IMPORTANT

A charged 30 μF capacitor is connected to a 27 mH inductor. The angular frequency of free oscillations of the circuit is

EASY
IMPORTANT

A 1.5μF capacitor is charged to 60V and a15mH coil is connected across it. Assuming that the circuit contains no resistance, what will be the maximum current in the coil?

HARD
IMPORTANT

An inductor and two capacitors are connected in the circuit as shown in figure. Initially capacitor A has no charge and capacitor B has CV charge. Assume that the circuit has no resistance at all. At t=0, switch S is closed, then given  LC=2π2×104s2 & CV=100 mC
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MEDIUM
IMPORTANT

A 1.5 μF capacitor is charged to 60 V. The charging battery is then disconnected and a 15 mH coil is connected in series with the capacitor so that LC oscillations occur. Assuming that the circuit contains no resistance, the maximum current in this coil shall be close to

MEDIUM
IMPORTANT

An LC circuit contains a 20 mH inductor and a 50 μF capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant at which the circuit which is closed be t=0. At what time the energy stored is completely magnetic?

HARD
IMPORTANT

A circuit has a self inductance of 1 henry and carries a current of 2 A. To prevent sparking when the circuit is broken, a capacitor which can withstand 400 volts is used. The least capacitance of the capacitor connected across the switch must be equal to

HARD
IMPORTANT

At a moment t=0, when the charge on capacitor C1 is zero, the switch is closed. If I0 be the current through the inductor at t=0, for  t>0 (initially, C2 is uncharged.)

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MEDIUM
IMPORTANT

The tuning circuit of a radio receiver has a resistance of 50 Ω, an inductor of 10 mH and a variable capacitor. 1 MHz radio wave produces a potential difference of 0.1 mV. The values of the capacitor to produce resonance is (Take π2=10)

MEDIUM
IMPORTANT

An oscillator circuit consists of an inductance of 0.5mH and a capacitor of 20μF. The equivalent frequency of the circuit is nearly