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Frequency refers to the number of waves that moves through a definite point in unit time. It can also be said that the number of vibrations or cycles that a body undergoes during one unit of time in a periodic motion.
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Keyterms: Frequency, periodic motion, sound wave, Hertz, angular frequency, ordinary frequency
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Frequency
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A vibrating item, like any other wave, causes a sound wave. A tuning fork or the sound of a human voice The particles in the medium vibrate back and forth at a specific frequency, regardless of the source of vibration. When a wave passes through a medium, the term frequency refers to how often the particles vibrate. The total number of complete vibrations per unit time is used to calculate frequency. A longitudinal wave, for example, has a frequency of 2000 vibrations per second if it vibrates 10,000 times in 5 seconds. Hertz is the most often used frequency unit.
1 Hertz = 1 vibration per second.
Our ears, as well as the ears of other animals, can detect the change in air pressure induced by sound waves. Frequencies between 20Hz and 20000 HZ are audible to humans. Infrasound is any sound with a frequency lower than the lowest we can hear, whereas ultrasound is anything with a frequency greater than 20000 HZ. The pitch is the sensation caused by the frequency. A high-frequency sound, such as a shriek, is a high-pitched sound, and a low-pitched sound is a low-frequency sound.
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Angular Frequency
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The angular frequency of a sinusoidal wave is defined as the angular displacement of any wave element per unit time or the rate of change of the waveform's phase. It is represented by the symbol. The formula for angular frequency and the SI unit are as follows:
Formula = ω = 2π/T = 2πf
SI unit = rads-1
Where,
- ω = angular frequency of the wave.
- T = time period of the wave.
- f = ordinary frequency of the wave.
SI Unit of Frequency
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When it comes to the SI unit of frequency, hertz is the most commonly used unit (Hz). Heinrich Hertz, a well-known German physicist, is remembered by the word. When we say one hertz, we usually indicate that something happens once per second. A display with a refresh rate of 1 hertz, for example, will refresh the picture once every second. Looking back in time, the traditional unit of measurement was revolutions per minute, abbreviated as r/min or rpm. One hertz equals 60 revolutions per minute.
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Things to Remember
- Unit of frequency is a part of CBSE class 11 syllabus unit 1, chapter 2 Units and Measurements.
- It carries a total of 4 to 6 periods and 4 to 6 marks.
- It acts as a parameter to understand the oscillatory rate and vibratory phenomenon.
- It helps in understanding the number of waves passed a definite point at unit time in case mechanical vibrations, audio signals, radio waves and light.
Sample Questions
Ques 1. What is the Time Period? (1 mark)
Ans. The time it takes any string element to complete an oscillation is defined as the time period of oscillation of a wave.
Ques 2. What is a wave? (1 mark)
Ans. A wave is a disturbance that travels from one spot to another through a medium.
Ques 3. What is the formula to find the frequency? (1 mark)
Ans. f = 1/T
Ques 4. What are the other common frequency units? (1 mark)
Ans. Megahertz, gigahertz, terahertz, beats per minute, frames per second, rounds per second, calls per second, times per second, and other frequency units are also commonly used.
Ques 5. On an average human heart is found to be beat 75 times in a minute. Calculate frequency and time period? (2 marks)
Ans. The beat frequency of heart = 75/ (1 min)
= 75/ (60 s)
= 1.25 s–1
= 1.25 Hz
The time period T = 1/ (1.25 s–1) = 0.8 s
Ques 6. What is the unit of frequency? (1 mark)
Ans. Hertz is the unit of frequency.
Ques 7. In a ripple tank, 10 ripples are produced per second. If the distance between a trough and a neighbouring crest is 12 cm, calculate the frequency and wavelength.(2 marks)
Ans. Frequency = Number of ripples produced per second
That is,
Frequency, f = 10 Hz
The frequency of the wave is 10 Hz.
Wavelength, l = 2 × 12 cm = 24 cm = 0.24 m
The wavelength of the wave is 0.24 m.
Ques 8. All electromagnetic waves travel through vacuum at the same speed. If a wave of frequency 7.5 GHz has a wavelength 4 cm, then the frequency of a wave with wavelength 6 km will be (assume both are electromagnetic waves propagating in vacuum): (1 mark)
Options:
(a) 40 kHz
(b) 50 kHz
(c) 5 GHz
(d) 2.5 MHz
Ans. b. 50 kHz
Ques 9. A typical sound wave travelling at 360 m/s has a frequency of 1200 Hz. Find its wavelength.(2 marks)
Ans. ν = 1200 Hz, v = 360 m/s,
λ = ?
λ = \(v \)/ν = 360/1200 = 0.3m
Ques 10. Define frequency. (1 mark)
Ans. Frequency refers to the number of waves that moves through a definite point in unit time. It can also be said that the number of vibrations or cycles that a body undergoes during one unit of time in a periodic motion.
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