C
CraftExam
medium difficulty5 min

Audible Range and Beyond

Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

In one line: Under 20 is infra; over 20,000 is ultra.

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Understand it

Sounds below 20 Hz are called infrasound, and sounds above 20,000 Hz are called ultrasound. Humans normally cannot hear infrasound or ultrasound, but some animals can detect frequencies outside the human hearing range. Ultrasound is useful because it can travel in a directed way and reflect from small objects.

Example

Bats use ultrasound for navigation, while elephants can communicate using low-frequency infrasound over long distances.

Rule to remember

Human audible range: approximately 20 Hz to 20,000 Hz.

Below 20 Hz is infrasound; above 20,000 Hz is ultrasound.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1A frequency of 15 Hz is below the human audible range, so it is infrasound.
  2. 2A frequency of 30,000 Hz is above the range, so it is ultrasound.

Method you can reuse

  1. 1Compare the given frequency with 20 Hz and 20,000 Hz.
  2. 2Below 20 Hz means infrasound, within the range means audible, and above 20,000 Hz means ultrasound.

Visual tip

A number-line diagram from below 20 Hz to above 20,000 Hz can show infrasound, audible sound, and ultrasound.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

A sound has frequency 25,000 Hz. Can an average human hear it, and what is it called?

Think first, then show answer
An average human cannot hear 25,000 Hz because it is above 20,000 Hz, so it is called ultrasound.

Common wrong answer

25,000 Hz is very loud sound.

Why it loses marks: Loudness depends on amplitude, while ultrasound is based on frequency.

Don't mix this up

Students often think ultrasound means very loud sound. It actually means sound with frequency above 20,000 Hz.

Exam tip

Write the numerical range with units: 20 Hz to 20,000 Hz. Then classify below as infrasound and above as ultrasound.

Audible Range and Beyond diagram

Open full screen to read every label clearly.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Exams may ask classification of given frequencies or examples of animals and devices using infrasound or ultrasound.
  1. 1

    Enough for 1 mark

    Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

  2. 2

    Add for 2 marks

    Example: Bats use ultrasound for navigation, while elephants can communicate using low-frequency infrasound over long distances.

  3. 3

    Add for 3 marks

    Sounds below 20 Hz are called infrasound, and sounds above 20,000 Hz are called ultrasound.

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