# Resonance

Resonance meaning in English is ‘to sound’ that is to produce sound. To produce sound the body must vibrate with the same wavelength as that of the other. Example of resonance is the simple harmonic motion exhibited by the pendulum.

## What is Resonance?

The definition of Resonance in physics is a phenomenon in which an external force or a vibrating system forces another system around it to vibrate with greater amplitude at a specified frequency of operation. The frequency at which the second body starts oscillating or vibrating at higher amplitude is called the resonant frequency of the body. The best examples of resonance can be observed in various musical instruments around us.

Whenever any person hits, strikes, strums, drums or tweaks any musical instrument, the instrument is set into oscillation or vibration at the natural frequency of vibration of the instrument. A unique standing wave pattern defines each frequency of vibration as a specific instrument. These natural frequencies of a musical instrument are known widely as the harmonics of the specified instrument. If a second interconnected object or instrument vibrates or oscillates at that specified frequency then the first object can be forced to vibrate at a frequency higher than its natural harmonic frequency. This phenomenon is known as resonance i.e. one object vibrating or oscillating at the natural frequency of another object forces the other object to vibrate at a frequency higher than its natural frequency.

## Example of Resonance

A classic example of resonance is the swinging of a person sitting on a swing. A swing is a very good example of an object in oscillating motion. Initially, the motion is slow and the swing doesn’t extend to its maximum potential. But once when the swing reaches its natural frequency of oscillation, a gentle push to the swing helps it maintain that amplitude of swing all throughout due to resonance.

In an ideal situation, with no friction at all, even that slight push won’t be necessary once the swing reaches its natural frequency for it to sustain the maximum amplitude forever. Also almost all musical instruments, like the flute, guitar etc work on the principle of resonance itself.

## What is Resonant Frequency?

The resonant frequency is also known as resonance frequency which is used in the series circuit when the inductive reactance is equal to the capacitive reactance. The resonant frequency is mathematically given as:

 $f_{0}=\frac{1}{2\pi \sqrt{LC}}$

Where,

• f0 is the resonant frequency
• L is the inductance
• C is the capacitance

Read more about sound resonance and parallel resonance and learn how it is valid in practical life only through BYJU’S engaging videos.

### When is a circuit said to be in resonance with respect to current and voltage?

A circuit is said to be in resonance when the current is in phase with the voltage that is applied. If the current is out of phase with respect to applied voltage, there is no resonance in the circuit. This concept is used in communications.

### Define Resonant frequency.

The resonant frequency is the oscillation of a system at its natural or unforced resonance.

### How to tune a parallel resonant circuit to a higher frequency?

A parallel resonant circuit can be tuned to a higher frequency by decreasing the capacitance.

### Give the expression of bandwidth for parallel resonant circuit.

The expression used for the bandwidth of the parallel resonant circuit is $Bandwidth=\frac{1}{RC}$.

### What is susceptance?

Susceptance is defined as an expression of ease with which alternating current flows through an inductance or a capacitance. It is equal to the reciprocal of reactance. Siemens is the unit of susceptance.

### Define quality factor.

Quality factor is defined as the product of 2 π and ratio of maximum energy stored to the energy dissipated per cycle. The expression used for quality factor is $Quality\;factor=\frac{I_{L}}{I}$

### What is resonance with respect to RLC circuit?

In a series RLC circuit, resonance is a condition in which the capacitive and inductive reactances are equal in magnitude.