Team Physics -
Created by: Team Physics -, Last Updated: April 25, 2024


What is Frequency?

Frequency refers to the number of complete cycles of a periodic event that occur in a specific unit of time. In the context of waves, like sound waves or light waves, it measures how many waves pass a point each second. Frequency is commonly expressed in units called hertz (Hz), where one hertz equals one cycle per second. This concept is crucial in physics, engineering, and various technology fields, helping to describe how often an event repeats over time.

Frequency (f) = Number of Cycles (n) / Time (t)

Frequency Formula

Frequency Formula

The formula for frequency is used to calculate how often something occurs within a specific interval of time. It is commonly expressed as:

f = 1/T

f = v/λ


Frequency in Terms of Time Period:

Formula : f = 1/T
  • Where:
  • f is the frequency in hertz (Hz),
  • T is the time it takes to complete one cycle, measured in seconds.

Frequency in Terms of Wavelength and Wave Speed:

Formula: f = v/λ
  • Where:
    • v is the wave speed in meters per second (m/s),
    • λ (lambda) is the wavelength of the wave in meters.

Frequency in Terms of Angular Frequency:

Formula: f=ω/2π
  • Where:
    • ω (omega) is the angular frequency.

Units of Frequency

Frequency is measured in units called hertz (Hz), where one hertz represents one cycle per second. This is the standard unit used internationally to indicate the number of times a periodic event occurs per second.

Besides hertz, frequency can also be expressed in multiples that reflect higher or lower values, such as:

  • Kilohertz (kHz): One thousand hertz.
  • Megahertz (MHz): One million hertz.
  • Gigahertz (GHz): One billion hertz.

These units are commonly used in various contexts, like radio frequencies, computer processors, and the transmission of digital data. The choice of unit typically depends on the frequency of the phenomenon being measured. For example, radio stations often broadcast at frequencies in megahertz, while computer CPUs operate in gigahertz.

Examples of Frequency

Examples of Frequency

1. Radio Broadcasting

  • Radio stations broadcast at specific frequencies. For instance, a station might broadcast at 98.7 MHz (megahertz). The frequency determines the radio wave’s position on the electromagnetic spectrum, which listeners tune into on their radios.

2. Sound Waves

  • Musical notes are distinguished by their frequencies. Middle C on a piano vibrates at about 261.6 Hz. Higher pitches have higher frequencies, while lower pitches have lower frequencies.

3. Wi-Fi Networks

  • Wi-Fi routers operate at frequencies like 2.4 GHz or 5 GHz. These frequencies allow the transmission of data over airwaves from the internet to your device.

4. Light Waves

  • The color of visible light depends on its frequency. For example, red light has a lower frequency than blue light. Ultraviolet light has even higher frequencies, which are invisible to the human eye.

5. Medical Imaging

  • MRI machines use radio frequency pulses to generate images of the body. These frequencies help in aligning the hydrogen atoms in the body, which are then detected to produce detailed images for medical diagnosis.

6. Clocks and Timekeeping

  • Quartz clocks use the frequency of vibrations of a quartz crystal to keep time. The crystal oscillates at a stable frequency of 32,768 Hz, which the clock circuitry uses to count seconds accurately.

Types of Frequency

1. Angular Frequency

  • Angular frequency is used primarily in physics to describe the rotation speed of an object and the oscillation rate of waves. It is measured in radians per second (rad/s). The formula for angular frequency is ω=2πf, where f is the standard frequency.

2. Natural Frequency

  • Natural frequency refers to the frequency at which a system tends to oscillate in the absence of any driving or damping force. It’s a fundamental property of dynamic systems and structures, crucial in engineering and physics.

3. Resonant Frequency

  • This is the frequency at which a system resonates at maximum amplitude. For example, each musical instrument has a resonant frequency at which it produces the loudest sound. This concept is also critical in circuits and mechanical systems.

4. Nyquist Frequency

  • In digital signal processing, the Nyquist frequency is half the sampling rate of a discrete signal processing system. It is the highest frequency that can be accurately represented when digitizing a signal, based on the sampling theorem.

5. Cut-off Frequency

  • The cut-off frequency is the frequency point in an electronic filter circuit at which the output power is reduced to half its peak value. It’s a key concept in electronics for designing filters and signal processing systems.

6. Frequency Range

  • This refers to the spread of frequencies a device or material can effectively transmit or receive. It is used to describe anything from the audible range of the human ear (typically 20 Hz to 20 kHz) to the operational frequency range of electronic devices.

7. Frequency Band

  • In telecommunications, a frequency band is a specific range of frequencies used for transmitting signals. Different bands are regulated and designated for particular uses, such as mobile communications, TV broadcasts, and Wi-Fi networks.

Relationship Between Frequency and Energy

The relationship between frequency and energy is a fundamental concept in physics, particularly evident in the behavior of waves and quantum mechanics. Here’s how frequency relates to energy:

Basic Principle

  • Energy and Frequency: The energy of a wave is directly proportional to its frequency. This means that higher frequency waves have more energy than lower frequency waves.

Mathematical Expression

  • The relationship between energy (E) and frequency (f) of a wave is given by the equation:
  • E = h × f
  • where:
    • E is the energy,
    • f is the frequency,
    • h is the Planck constant (approximately 6.626×10−346.626×10−34 joule seconds).

Applications and Examples

  1. Light Waves: In the electromagnetic spectrum, higher frequency light (like ultraviolet rays) carries more energy per photon than lower frequency light (like infrared rays). This is why ultraviolet rays can cause sunburns, as they have enough energy to damage skin cells.
  2. Radio Waves vs. Gamma Rays: Radio waves have very low frequencies compared to gamma rays. Consequently, gamma rays, which are high-frequency electromagnetic waves, carry significantly more energy and can penetrate materials that radio waves cannot.
  3. Quantum Mechanics: In the realm of quantum mechanics, this relationship is crucial. Photons (the particle aspect of light) have energies that are proportional to their frequencies. Higher frequency photons (e.g., gamma rays) are much more energetic than lower frequency photons (e.g., radio waves).


The direct proportionality of frequency and energy has significant implications in technology, medicine, and natural phenomena. For instance, in medical imaging, different frequencies of electromagnetic waves are chosen based on the energy levels required to penetrate body tissues without causing harm. In communication technology, the choice of frequency impacts the energy use and range of the transmission.

Relation between Frequency and Wavelength

Frequency (f)The number of cycles of a wave that pass a point per second, measured in hertz (Hz).
Wavelength (λ)The distance over which the wave’s shape repeats, measured in meters (m).
RelationFrequency and wavelength are inversely proportional to each other in a wave. This means when the frequency increases, the wavelength decreases, and vice versa.
FormulaThe relationship is given by the formula v=f×λ, where v is the wave speed in meters per second (m/s).
ImplicationKnowing one of these properties and the speed of the wave allows you to calculate the other. This is crucial in fields like physics, engineering, and telecommunications.

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