What is an Infrasonic Wave?

S4-SA1-0201

Grade Level:

Class 8

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

An infrasonic wave is a sound wave that has a frequency lower than what the human ear can hear. Humans can typically hear sounds between 20 Hz and 20,000 Hz, so infrasonic waves are those with a frequency below 20 Hz.

Simple Example

Quick Example

Imagine a big, heavy truck rumbling past your house. Sometimes, you don't just hear the sound, but you feel a deep vibration in your chest or through the ground. This deep rumble often contains infrasonic waves, which are too low-pitched for your ears to fully register as a clear sound.

Worked Example

Step-by-Step

Let's say a sound wave has a frequency of 15 Hz. Is it an infrasonic wave?

1. Recall the human hearing range: Humans can hear sounds typically from 20 Hz to 20,000 Hz.
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2. Compare the given frequency (15 Hz) with the lower limit of human hearing (20 Hz).
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3. Since 15 Hz is less than 20 Hz, it falls below the audible range for humans.
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4. Therefore, a sound wave with a frequency of 15 Hz is an infrasonic wave.

Answer: Yes, it is an infrasonic wave.

Why It Matters

Understanding infrasonic waves is crucial in fields like Space Technology for monitoring rocket launches and in Climate Change studies to track natural disasters like earthquakes and volcanic eruptions. Scientists and engineers use this knowledge to design early warning systems and study animal communication, helping protect lives and understand our planet better.

Common Mistakes

MISTAKE: Thinking infrasonic waves are extremely loud sounds. | CORRECTION: Infrasonic waves are not defined by their loudness (amplitude) but by their very low frequency, making them inaudible to humans.

MISTAKE: Confusing infrasonic waves with ultrasonic waves. | CORRECTION: Infrasonic waves have frequencies BELOW 20 Hz (inaudible low pitch), while ultrasonic waves have frequencies ABOVE 20,000 Hz (inaudible high pitch).

MISTAKE: Believing infrasonic waves cannot travel far. | CORRECTION: Due to their long wavelengths, infrasonic waves can actually travel very long distances and penetrate through obstacles, which is why they are used to monitor distant events.

Practice Questions

Try It Yourself

QUESTION: A dolphin produces a sound with a frequency of 10 Hz. Is this an infrasonic wave for humans? | ANSWER: Yes, because 10 Hz is below the human hearing threshold of 20 Hz.

QUESTION: An earthquake generates seismic waves, some of which have frequencies around 5 Hz. Explain why these would be classified as infrasonic waves. | ANSWER: These waves are classified as infrasonic because their frequency (5 Hz) is significantly lower than the minimum frequency (20 Hz) that the human ear can detect.

QUESTION: If a sound wave has a wavelength of 34 meters and travels at a speed of 340 m/s, calculate its frequency and determine if it is an infrasonic wave. (Hint: Speed = Frequency x Wavelength) | ANSWER: Frequency = Speed / Wavelength = 340 m/s / 34 m = 10 Hz. Since 10 Hz is less than 20 Hz, it is an infrasonic wave.

MCQ

Quick Quiz

Which of the following frequencies represents an infrasonic wave?

25 Hz

200 Hz

10 Hz

25,000 Hz

The Correct Answer Is:

Infrasonic waves have frequencies below 20 Hz. Out of the given options, only 10 Hz falls into this range. 25 Hz and 200 Hz are within the human audible range, and 25,000 Hz is an ultrasonic wave.

Real World Connection

In the Real World

In India, the National Centre for Seismology uses sophisticated sensors to detect infrasonic waves generated by earthquakes, volcanic activity, and even meteor impacts. This helps scientists understand geological events better and can contribute to early warning systems, much like how ISRO uses advanced tech to track space objects.

Key Vocabulary

Key Terms

FREQUENCY: The number of wave cycles passing a point per second, measured in Hertz (Hz). | HERTZ (Hz): The unit of frequency, representing one cycle per second. | AUDIBLE RANGE: The range of sound frequencies that the human ear can detect, typically 20 Hz to 20,000 Hz. | WAVELENGTH: The distance between two consecutive crests or troughs of a wave.

What's Next

What to Learn Next

Now that you understand infrasonic waves, you should explore 'What is an Ultrasonic Wave?' This will help you complete your knowledge of the sound spectrum and understand how sound is used in different technologies, from medical scans to pest control. Keep up the great work!