## Forced Oscillations and Resonance – Class 11 | Chapter – 14 | Physics Short Notes Series PDF for NEET & JEE

Forced Oscillations and Resonance: Forced oscillations occur when an external force is applied to a system undergoing Simple Harmonic Motion (SHM). This external force can be periodic or non-periodic and can cause the system to oscillate at a frequency that is different from its natural frequency.

When an external force is applied to a system undergoing SHM, the system responds by oscillating at the frequency of the external force. The amplitude of the oscillations depends on the frequency of the external force and the characteristics of the system. The amplitude is maximum when the frequency of the external force is equal to the natural frequency of the system. This is known as resonance.

## Forced Oscillations and Resonance

### Resonance

Resonance is a phenomenon that occurs when a system is subjected to an external force or stimulus that has a frequency that matches the natural frequency of the system. When the frequency of the external force matches the natural frequency of the system, the system responds with an amplified response, which is referred to as resonance.

Resonance can occur in many different physical systems, including mechanical, electrical, and acoustic systems. Examples of resonance include:

• A swing: When someone pushes a swing at the right frequency, the swing will oscillate back and forth with a large amplitude, which is an example of mechanical resonance.
• An acoustic guitar: When a guitar string is plucked, it vibrates at a particular frequency, which resonates with the air in the body of the guitar, amplifying the sound.
• A bridge: When a bridge is subjected to high winds, the bridge can vibrate at its natural frequency, causing it to resonate and potentially leading to structural damage.
• MRI machine: An MRI machine uses radio frequency pulses to excite hydrogen atoms in the body, which then resonate at a particular frequency and emit a signal that is used to create images.

Resonance is important in many areas of science and engineering, and it is both a useful tool and a potential source of problems, depending on the application.

### Types of Resonance

Resonance is a phenomenon that occurs in many different systems and can take on many different forms. Here are some types of resonance:

• Mechanical resonance: This occurs when a mechanical system, such as a tuning fork or a musical instrument, vibrates at its natural frequency. When an external force matches this frequency, the system will vibrate with greater amplitude.
• Electrical resonance: This occurs in electrical circuits, where energy is stored in the form of electrical charge or magnetic fields. When an AC voltage is applied to an electrical circuit at its resonant frequency, the circuit will absorb more energy and resonate.
• Magnetic resonance: This occurs in magnetic fields when the frequency of the applied electromagnetic radiation matches the natural frequency of the sample. Magnetic resonance is widely used in medical imaging to visualize the internal structure of the body.
• Acoustic resonance: This occurs when sound waves are reflected and reinforced within a closed space or cavity, creating a standing wave with a frequency determined by the dimensions of the cavity.
• Molecular resonance: This occurs when the natural vibration frequency of a molecule matches an external radiation frequency, causing the molecule to absorb energy and become excited.
• Nuclear magnetic resonance: This is a type of magnetic resonance that is used to study the behavior of atomic nuclei in a magnetic field, and is widely used in chemical analysis and medical imaging.

These are just a few examples of the many types of resonance that exist in different systems.

### Forced Oscillations

Forced oscillation is a type of oscillation or vibration that occurs when a system is subjected to a periodic external force or driving force that is different from its natural frequency. The external force may be applied as a continuous or intermittent force, and can be either harmonic or non-harmonic in nature.

The response of a system to a forced oscillation depends on the relationship between the frequency of the external force and the natural frequency of the system. When the frequency of the external force matches the natural frequency of the system, a phenomenon called resonance occurs, where the amplitude of the oscillations can become very large. This can lead to damage or failure of the system if it is not designed to withstand the stresses caused by resonance.

When the frequency of the external force is different from the natural frequency of the system, the system undergoes forced oscillations that are characterized by a steady-state response. The amplitude of the steady-state response depends on the magnitude and frequency of the external force, as well as the damping of the system. The steady-state response can be calculated using mathematical models that describe the behavior of the system.

Forced oscillations occur in many physical systems, such as mechanical systems, electrical circuits, and biological systems. They are an important phenomenon to understand in order to design and analyze systems that are subjected to external forces.

### Types of Oscillations

Oscillation is a repetitive motion or variation that occurs around a stable equilibrium point. Here are some types of oscillations:

• Harmonic oscillation: This is a type of oscillation in which the restoring force is directly proportional to the displacement from the equilibrium point. Examples of harmonic oscillators include a mass on a spring and a pendulum.
• Damped oscillation: This occurs when an oscillator experiences a resistive force that causes its amplitude to decrease over time. Examples of damped oscillators include a car suspension system and a guitar string.
• Forced oscillation: This occurs when an external force is applied to an oscillator, causing it to vibrate at a frequency different from its natural frequency. Examples of forced oscillators include a swing pushed by a person and a musical instrument played by a musician.
• Nonlinear oscillation: This occurs when the restoring force of an oscillator is not directly proportional to the displacement from the equilibrium point. Nonlinear oscillations can exhibit complex and unpredictable behavior, such as chaos. Examples of nonlinear oscillators include a double pendulum and a Van der Pol oscillator.
• Relaxation oscillation: This occurs in systems that have a delay between the application of a stimulus and the response of the system. Examples of relaxation oscillators include a heartbeat and a blinking eye.
• Parametric oscillation: This occurs when the properties of an oscillator are modulated by an external parameter that changes over time. Examples of parametric oscillators include a swing with varying length and a radio receiver with a varying capacitor.

These are just a few examples of the many types of oscillations that occur in physical systems.

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