Tag: resonance

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Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

Resonance is a special case of $\underline{           }$ vibrations, when frequency of the driving force is$\underline{           }$ natural frequency of the body.

  1. forced, equal to the

  2. particle , more then the

  3. wave, equal to the

  4. forced, less than the
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Resonance is a special case of forced vibrations, when frequency of the driving force is equal to the natural frequency of the body.
Resonance is the result of an external force vibrating at the same frequency as the natural frequency of a system. Natural frequency is a characteristic of every machine, structure and even animals. Often, resonance can be confused with the natural frequency or critical frequency. If equipment is operating in a state of resonance, the vibration levels will be amplified significantly, which can cause equipment failure and plant downtime. It is, therefore, important that the running speed of equipment be out of the resonance range.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

A forced oscillator is acted upon by a force $F={ F } _{ \circ  }sin\omega t.$. The amplitude of oscillation is given by $\displaystyle\frac{55}{\sqrt{2\omega^2 - 36\omega + 9}}$. The resonant angular frequency is

  1. $2\space unit$
  2. $9\space unit$
  3. $18\space unit$
  4. $36\space unit$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

At resonance, amplitude of oscillation is maximum
$\quad \Rightarrow 2\omega^2 - 36\omega + 9$ is maximum
$\quad \Rightarrow 4\omega - 36 = 0$ (derivative is zero)
$\quad \Rightarrow \omega = 9$

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

Imagine a child sitting on a swing in a park and the child's mother is pushing the swing from the back. The mother maintains the same tempo as the motion of the swing. If the mother tries to push at a faster tempo, the arc of the swing will:

  1. increase

  2. decrease

  3. remain the same

  4. become zero, i.e., the swing will stop
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As the mother maintains the same tempo as the motion of the swing, it means frequency of mother and the swing is same, there is resonance. When mother tries to push at a faster tempo, frequency of mother changes and resonance is disturbed due to which, the arc of swing (amplitude) decreases.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

A vibrating object will pick out its __________ from a complex excitation and vibrate at those frequencies.

  1. resonant frequency

  2. natural frequency

  3. both

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A vibrating object will pick out its resonant frequencies from a complex excitation and vibrate at those frequencies, essentially "filtering out" other frequencies present in the excitation.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

State whether the given statement is True or False :
By tuning ultra sound waves to the natural frequency of a kidney stone, we can rely on resonance to pulverize the stone.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

By turning ultrasound waves to the natural frequency of a kidney stone, we rely on resonance to parcels which the stones consist of vibrate with large amplitude and at a certain moment, this vibration causes breakdown of stone into pieces. So the given statement is true.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

Which one does not work on principles of resonance?

  1. T.V

  2. Radio

  3. Microwave oven

  4. Bulb
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Resonance in an electrical circuit is a phenomenon in which the inductive reactance and the capacitive reactance become equal and cancel each other.

As a result, the impedance of the circuit becomes the least and maximum current flows through the circuit. This happens only at a particular frequency of the AC power supply, known as resonant frequency. 
All the devices except bulb work on this principle. The circuit in them is tuned in order to make their resonant frequency matching with the desired one. This is done by adjusting the values of the inductor or the capacitor.
In a bulb, there is only pure resistance and no reactive component. There is no question of resonance.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

In a resonance column experiment, the first resonance is obtained when the level of the water in tube is $20 cm$ from the open end. Resonance will also be obtained when the water level is at a distance of

  1. $40 cm$ from the open end.
  2. $60 cm$ from the open end.
  3. $80 cm$ from the open end.

  4. data insufficient.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In a closed pipe : length of the pipe is length of the air column in fundamental.

$\dfrac { \lambda  }{ 4 } =20cm$ 
${ 2 }^{ nd }$ harmonic resonance $=\dfrac { 3\lambda  }{ 4 } =3\times 20=60cm$

$\therefore $  Option (B) is correct.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

Assertion : In the ideal case of zero damping, the amplitude of simple harmonic motion at resonance is infinite.
Reason : All real systems have some damping.

  1. If both assertion and reason are true and reason is the correct explanation of assertion.

  2. If both assertion and reason are true and reason is not the correct explanation of assertion.

  3. If assertion is true but reason is false.

  4. If both assertion and reason are false.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If there was no damping in the swing, the swing would move with larger and larger amplitudes. However, most physical systems have damping, which limits the size of the amplitude. If you don not have damping the amplitudes will go to infinity.

So, Assertion and reason both are true. But reason is not current explanation for the assertion.

Multiple choice physics oscillations introduction to sound free, forced and damped oscillations resonance

What impulse need to be given to a body of mass $m$, released from the surface of earth along a straight tunnel passsing through centre of earth, at the centre of earth, to bring it to rest(Mass of earth $M$, radius of earth R) 

  1. $m \sqrt { \dfrac { G M } { R } }$
  2. $\sqrt { \dfrac { G M m } { R } }$
  3. $m \sqrt { \dfrac { G M } {2 R } }$
  4. $zero$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At the center of the Earth, the gravitational force is zero. Since the body is already at the center and has reached it due to gravity, its velocity is at a maximum; however, the question asks for the impulse to bring it to rest. If the body is released from the surface, it will oscillate through the center. At the exact center, the net force is zero, but the body has kinetic energy. However, in the context of standard physics problems of this type, the force at the center is zero, and if we assume the body is meant to be at rest at the center, the impulse required is zero if it is already there, or the question implies a conceptual trick.