Resonance

Q.

What are Barkhausen conditions for Oscillation?

Q. As the frequency of an $AC$ circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?

1. Inductor and capacitor
2. Resistor and inductor
3. Resistor, inductor and capacitor
4. (a) and (c) above

Q. Two mutually perpendicular simple harmonic vibrations have the same amplitude, frequency and phase. When they superimpose, the resultant form of vibration will be

1. a circle
2. a straight line
3. an ellipse
4. a parabola

Q. A series $\text{LCR}$ circuit containing a resistance of $120\Omega$ has angular resonance frequency ${\omega }_0=4\times {10}^5{\text{rad s}}^{–1}$. At resonance, the voltage across resistance and inductance are $60\text{V}$ and $40\text{V}$ respectively. When angular frequency $\omega =n\times {10}^5{\text{rads}}^{–1}$, the current in the circuit lags the voltage by ${45}^{\circ }.$ The value of $n$ is (integer only).

Q. In LCR circuit, resonant frequency is $600\text{Hz}$ and half power points are at $650$ Hz and $550\text{Hz}$. The quality factor is

1. $\frac{1}{6}$
2. $\frac{1}{3}$
3. $6$
4. $3$

Q. A closed organ pipe, of length $1.5\text{m}$ and filled with a gas, is resonated in its fundamental mode with the help of a tuning fork. Another open pipe of same length but filled with air resonates with the same fork. The room temperature is ${30}^{\circ }\text{C}$. If the speed of sound in air at ${30}^{\circ }\text{C}$ is $340\text{m/s}$, then the speed of sound in the first gas at ${30}^{\circ }\text{C}$ will be

1. $340\text{m/s}$
2. $680\text{m/s}$
3. $510\text{m/s}$
4. $322.5\text{m/s}$

Q. A resonant ac circuit contains a capacitor of capacitance ${10}^{-6}F$ and an inductor of ${10}^{-4}H$. The frequency of electrical oscillations will be

1. ${10}^{5}Hz$
2. $10Hz$
3. $\frac{{10}^5}{2\pi }Hz$
4. $\frac{10}{2\pi }Hz$

Q. An $AC$ source of emf $E=200\sin \left[100t\right]V$ is connected to a choke coil of inductance $1H$ and resistance $100\Omega$. Find the average power consumed.

1. $400W$
2. $200W$
3. $100W$
4. given information is insufficient

Q. The value of current at resonance in a series $\text{LCR}$ circuit is affected by the value of

1. $\text{R}$ only
2. $\text{C}$ only
3. $\text{L}$ only
4. $\text{L, C}$ and $\text{R}$

Q. Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field $B=B_0\hat{k}$.

1. The charge to mass ratio satisfy:
   ${\left(\frac{e}{m}\right)}_1+{\left(\frac{e}{m}\right)}_2=0$.
2. They necessarily represent a particle-antiparticle pair.
3. They must have equal charges.
4. They have equal $z$- components of momenta.

Q.

A power transmission line feeds input power at 2300 V to a stepdown transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230 V?

Q. For wattless power in an AC circuit, the phase difference between the current and the voltage is -

1. $0^{\circ }$
2. ${90}^{\circ }$
3. ${45}^{\circ }$
4. Not possible

Q.

A Kundt's tube apparatus has a steel rod of length it m clamped at the centre. It is vibrated in its fundamental mode at a frequency of 2600 Hz. The lycopodium powder dispersed in the tube collects into heaps separated by 6.5 cm. Calculate the speed of sound in steel and in air.

Q. For de-excitation of electrons from n = 5 to n = 2 possible number of spectral lines emitted wil be

Q.

(i) For the wave on a string described in Exercise 15.11, do all the points on the string oscillate with the same (a) frequency, (b) phase, (c) amplitude? Explain your answers. (ii) What is the amplitude of a point 0.375 m away from one end?

Q.

Which of the following performs modulation and demodulation?

1. Coaxial cable

2. Satellite

3. Modem

4. Optical fibre

5. None of these

Q. In the AC network shown in the figure, the rms current flowing through the inductor and capacitor are $0.6\text{A}$ and $0.8\text{A}$, respectively. Then, the current coming out of the source is -

1. $1.0\text{A}$
2. $1.4\text{A}$
3. $0.2\text{A}$
4. $1.8\text{A}$

Q.

Choose the correct option in each of the following:

The rapid back and forth movement of a body about its mean position is called

1. Time period

2. Frequency

3. Amplitude

4. Vibration

Q. During the phenomenon of resonance

1. The amplitude of oscillation becomes large
2. The frequency of oscillation become large
3. The time period of oscillation becomes large
4. All of the above

Q. For a series LCR circuit, power factor at resonance is equal to -

1. $1$
2. $0.5$
3. $0.7$
4. $0.9$

Q. For an $LCR$ circuit, resonance frequency is ${\omega }_o$ and bandwidth is $△\omega$, then

1. circuit is inductive for $({\omega }_o-\frac{△\omega }{2})$
2. circuit is capacitive for $({\omega }_o+\frac{△\omega }{2})$
3. circuit is resistive for $({\omega }_o-\frac{△\omega }{2})$
4. circuit is inductive for $({\omega }_o+\frac{△\omega }{2})$

Q.

When a body executes forced oscillations of large amplitude, the frequency of external periodic force is same as the natural frequency of oscillations of the system. This phenomenon is known as ___________________ .

Q.

A person is turning the radio station to a particular station. What is the person trying to do to tune it?

Q.

Two sitar strings A and B playing the note ‘Ga’ are slightly out of tune and produce beats of frequency 6 Hz. The tension in the string A is slightly reduced and the beat frequency is found to reduce to 3 Hz. If the original frequency of A is 324 Hz, what is the frequency of B?

Q. A hollow pipe of length $0.8\text{m}$ is closed at one end. At its open end a $0.5\text{m}$ long uniform string (fixed at both ends) is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is $50\text{N}$ and the speed of sound is $320{\text{ms}}^{-1}$, the mass of the string is

1. $5\text{g}$
2. $10\text{g}$
3. $20\text{g}$
4. $40\text{g}$

Q. A series $RLC$ circuit has inductance of $0.12\text{H}$, capacitance of $480\text{nF}$ and resistance of $23\Omega$ is connected to a $230\text{V}$ AC supply whose frequency can be varied. What is the source frequency for which current amplitude is maximum? Also, find the maximum value of current.

1. $500.5\text{Hz},19.1\text{A}$
2. $663.5\text{Hz},14.1\text{A}$
3. $809.9\text{Hz},22.5\text{A}$
4. $700.5\text{Hz},18.1\text{A}$

Q. During the phenomenon of resonance

1. The amplitude of oscillation becomes large
2. The frequency of oscillation become large
3. The time period of oscillation becomes large
4. All of the above

Q. A resonant ac circuit contains a capacitor of capacitance ${10}^{-6}F$ and an inductor of ${10}^{-4}H$. The frequency of electrical oscillations will be

1. ${10}^{5}Hz$
2. $10Hz$
3. $\frac{{10}^5}{2\pi }Hz$
4. $\frac{10}{2\pi }Hz$

Q. two electrons are release toward each other with equal velocities of 10^6 m/s what will be the closest appoach between them.

Q. Which of the following is a type of polarization?

1. Linear polarization
2. Circular polarization
3. Elliptical polarization
4. All of these