What is Hertz?
The hertz which has the symbol: Hz is the derived unit of frequency in the International System of Units that is known as the SI and is defined as one cycle per second. It is said to be named after Heinrich Rudolf Hertz.
Scientist Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the waves which are electromagnetic and this was predicted by James Clerk Maxwell's equations of electromagnetism. The unit that is of frequency is the cycle per second was named "hertz" in his honour.
Here, we are going to discover a few more things about the topic.
Why is Hertz Used?
In the field of physics. hertz which is often denoted by the symbol ‘Hz’ can be defined as the derived unit of frequency. We can say this as per the International System of Units. It is an important thing to note that frequencies are often expressed in multiples of Hertz which is such as kilohertz that is denoted by kHz, megahertz denoted by MHz, gigahertz is denoted by GHz. The SI Unit based on the unit of the Hertz is second-1 or we can say that s-1. We need to notice that the Hertz is an SI derived unit.
In English, we can say that "hertz" is also used as the plural form. MHz is the megahertz or 106 Hz. Similarly, GHz that is gigahertz is 109 Hz and THz or terahertz is 1012 Hz.100 Hz means "one hundred cycles per second", and so on. The unit usually may be applied to any event which is periodic— for example, we can say that a clock might be said to tick at 1 Hz or we can say that a human heart might be said to beat at 1.2 Hz.
Hertz as Unit of Frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency which emphasizes the contrast to the frequency that is the spatial and angular frequency. We can say that frequency is measured in hertz that is denoted by Hz which is equal to one occurrence of a repeating event per second.
The period is said to be the duration of time of one cycle in a repeating event so the period is said to be the reciprocal of the frequency. For example, we can say that if a newborn baby's heart beats at a frequency of 120 times a minute then it is 2 hertz is its period denoted by the letter T, the time interval which is between beats is half a second that is said to be 60 seconds divided by 120 beats.
Hertz Applications
Frequency is an important parameter that is used in science and engineering to specify the rate of oscillation and the phenomenon of vibratory vibrations such as mechanical vibrations of the audio signals or the sound radio waves and light.
The frequency of any phenomenon can be expressed in hertz but we can say that the term is used most frequently in connection with alternating currents which are electric and the waves which are electromagnetic such as light, radar, etc and sound as well. It is said to be a part of the International System of Units based on the metric system. The unit was adopted in October 1933 by a committee of the International Commission of Electrotechnical and is in widespread use today that is said to be although it has not entirely replaced the expression which is the cycles per second.
An older method that is of measuring the frequency of rotating or vibrating objects is to use a stroboscope. This is said to be intense repetitively flashing the light that is strobe light whose frequency can be adjusted with a calibrated timing circuit.
FAQs on Hertz
1. What is the official definition of Hertz (Hz) in Physics?
In Physics, the Hertz (Hz) is the SI derived unit of frequency. It is defined as one cycle per second. This means if a wave or an oscillation completes one full cycle of its repeating motion in one second, its frequency is 1 Hz. The unit is named in honour of the German physicist Heinrich Rudolf Hertz for his significant contributions to the field of electromagnetism.
2. How is Hertz (Hz) related to the time period of a periodic event?
Hertz (frequency) and time period are inversely proportional to each other. The time period (T) is the time taken to complete one cycle, while frequency (f) is the number of cycles per second. The relationship is given by the formula:
f = 1 / T
For example, if a pendulum has a time period of 2 seconds to complete one full swing, its frequency is 1 / 2 = 0.5 Hz.
3. What are some common multiples of Hertz and where are they used?
In science and technology, very high frequencies are common, so multiples of Hertz are used:
- Kilohertz (kHz): 1,000 Hz. Used in the context of audible sound frequencies.
- Megahertz (MHz): 1,000,000 Hz. Commonly used for FM radio station frequencies and older computer processor speeds.
- Gigahertz (GHz): 1,000,000,000 Hz. Used to measure the clock speed of modern computer CPUs, Wi-Fi bands, and mobile networks.
- Terahertz (THz): 1,000,000,000,000 Hz. Used in advanced imaging and spectroscopy, often referred to as the 'terahertz gap' in the electromagnetic spectrum.
4. Can you provide some real-world examples of phenomena measured in Hertz?
Hertz is used to measure the frequency of various periodic events in the real world:
- Alternating Current (AC): The standard frequency of household electricity in India is 50 Hz.
- Sound Waves: The range of human hearing is typically between 20 Hz and 20,000 Hz (20 kHz). The pitch of a sound is determined by its frequency.
- Computer Processors (CPU): The speed is measured in Gigahertz (GHz), indicating billions of processing cycles per second.
- Electromagnetic Waves: Radio stations broadcast at specific frequencies in kHz or MHz, while mobile phones operate in the MHz or GHz range.
5. Why is the SI unit of frequency specifically named 'Hertz'?
The unit is named in honour of Heinrich Rudolf Hertz (1857-1894). He was a German physicist who was the first to provide conclusive experimental proof of the existence of electromagnetic waves, which had been predicted by James Clerk Maxwell's equations. Naming the unit of frequency after him acknowledges his foundational work that paved the way for radio, television, and modern wireless communication.
6. How does the frequency in Hertz determine the characteristics of a sound wave?
For a sound wave, frequency directly determines its pitch. A high-frequency sound wave results in a high-pitched sound (like a whistle), while a low-frequency sound wave results in a low-pitched sound (like a bass drum). The frequency of sound is measured in Hertz, and the human ear can typically perceive frequencies in the range of 20 Hz to 20,000 Hz. Frequencies below this range are called infrasound, and those above are called ultrasound.
7. What is the relationship between the frequency (in Hz) of an electromagnetic wave and its energy?
The frequency of an electromagnetic (EM) wave is directly proportional to its energy. According to the Planck-Einstein relation (E = hf), the energy (E) of a photon is the product of its frequency (f) and Planck's constant (h). This means waves with a higher frequency, such as X-rays or gamma rays, carry significantly more energy than waves with a lower frequency, such as radio waves.
8. What is the key difference between frequency (measured in Hertz) and angular frequency?
While both describe the rate of oscillation, they use different units and contexts:
- Frequency (f) is measured in Hertz (Hz), which represents the number of complete cycles or oscillations per second.
- Angular Frequency (ω) is measured in radians per second (rad/s). It is more commonly used in the mathematical description of rotational motion and sinusoidal waves (like in SHM and AC circuits).
They are related by the formula ω = 2πf, because one complete cycle is equivalent to 2π radians.
9. In which CBSE Physics chapters is the concept of Hertz most important for the 2025-26 syllabus?
As per the CBSE 2025-26 syllabus, the concept of Hertz (frequency) is fundamental in several key chapters:
- Class 11 Physics: It is crucial in Chapter 14 (Oscillations) and Chapter 15 (Waves), where it is used to describe simple harmonic motion, sound waves, and wave properties.
- Class 12 Physics: It is essential in Chapter 7 (Alternating Current), where the frequency of the AC mains (50 Hz) is a core parameter, and in Chapter 8 (Electromagnetic Waves), where the entire spectrum is classified by frequency.
