[Physics Class Notes] on Sharpness of Resonance Pdf for Exam

To define the Sharpness of Resonance, it’s necessary to understand what Resonance is? The term ‘Resonance’ derived from the field of acoustics, especially the sympathetic Resonance detected in musical instruments, e.g., when one string starts to vibrate and produce sound after a different one is struck. Let’s know the definition of Resonance in brief to have a better understanding on the ‘sharpness of Resonance’. 

 

Resonance Definition:

As the amplitude increases with the excitation of frequencies, a system’s tendency to vibrate also increases. This is defined as Resonance. The maximum frequency following which the amplitude is also maximum is called resonant frequency. To define the Sharpness of Resonance, the Q factor is used. When the matching vibrations of an object make another object’s oscillations increase its amplitude, this procedure is called Resonance.

 

In Physics, Resonance can also be defined as a phenomenon in which an external force or an external vibrating system makes another vibrating system (lying near the external vibrating system), vibrate at a higher level of frequency and amplitude at a specified frequency of operation than the system’s natural set of frequency (natural harmonic frequency).

 

The formula used to calculate the resonant frequency of a single continuous-wave can be defined as –

[nu = lambda f]

 

There are many types of Resonance that exist in this Physical world, some of them are as follows:

Mechanical Resonance: One great example of mechanical Resonance is swings.

 

Acoustic Resonance: The classic example of acoustic Resonance, can be the breaking of glass with nothing but sound at the precise resonant frequency of the glass.

 

Electrical Resonance: The various types of Resonance that happen in electrical circuits are all examples of electrical Resonance.

 

The Sharpness of Resonance Definition:

The depletion of an oscillating wave with respect to time is called the sharpness of the Resonance. It relates to the energy decay that happens in an oscillating system. It is mainly defined by the Q factor. 

 

The Sharpness of Resonance is dependent on mainly two factors. These are:

 

Amplitude: It is defined as the height of a wave which is moving in a uniform motion. The amplitude varies inversely with the sharpness of the Resonance. Higher the amplitude, less is the sharpness of the Resonance. And lesser the amplitude, higher is the sharpness of the Resonance. 

 

Damping: It is defined as the effect in which the amplitude of the wave is reduced with time. It can be both artificial or natural. Damping is directly related to the sharpness of the Resonance. An increase in damping leads to an increase in Resonance’s sharpness, and the converse also holds true.

 

Definition of Q Factor:

After knowing Resonance and Sharpness of Resonance, let us help you understand what Q factor is and its use. 

 

Q factor stands for the quality factor. It does not have any dimensions. It is used to characterise the centre frequency and bandwidth of the resonator and the underdamped resonator. 

 

It is represented mathematically as:

Q= Restore/Lost _{per cycle}

 

For an RF resonant circuit, the Q factor is given with:

Q= F0/F_3dB

 

Resonance in Series LCR Circuit:

The phenomenon of Resonance can be observed in an LCR Circuit arranged in series. The circuit is in Resonance during its Resonance frequency fr which happens when X_L=X_c. 

 

The resonant frequency is given by the formula:

fr= 1/2π√LC

 

Now, according to the conditions:

When current is maximum: f=f_r

 

The following conditions are applicable in the given series of RLC circuit:

• f_r: Purely capacitive

• f>f_r: Purely inductive

• f=f_r: Purely resistive

 

During Resonance:

The following aspects are observed when the circuit is in Resonance:

• Z=R, this implies that during Resonance, the impedance of the circuit is equal to R and is at its minimum value. 

• The RMS (root mean square) value in the circuit is at its maximum, and the Resonance is equal to V_rms/R. 

• The current and applied voltage are in phase.

• The power dissipation taking place in the circuit is in their maximum value.

 

Quality Factor: Sharpness of Resonance

The quality factor (Q) is a measure of the Sharpness of Resonance in the series RLC circuit. It is given by:

Q= (⍵_rL/R)

 

Power Factor:

In an AC circuit, the power factor is defined as the ratio of true power dissipation to the apparent power dissipation, represented using:

cos Φ= R/Z

 

The power factor for the AC circuit lies between the range of 0 and 1. 

Purely inductive circuit= 0

Purely resistive circuit= 1