MPPSC 2018 Prelims Q7: What is the audible range (hearing range) of

Q: What is the answer to MPPSC 2018 Prelims Q7?

A. Correct — A, 20 Hz to 20000 Hz. A healthy young human ear can hear sound whose frequency lies roughly between 20 Hz and 20,000 Hz (20 kHz). Below 20 Hz the sound is infrasonic and above 20,000 Hz it is ultrasonic — both are inaudible to us. (This upper limit falls with age.)

MPPSC 2018 Prelims Paper-I · Question 7 of 100

Verified against the official question paper. Answer as per the official MPPSC answer key.

What is the audible range (hearing range) of humans?

(a)20 Hz – 20000 Hz
(b)80 Hz – 100 Hz
(c)2 lac Hz – 4 lac Hz
(d)0 Hz – 20 Hz

Answer

Why

Correct — A, 20 Hz to 20000 Hz. A healthy young human ear can hear sound whose frequency lies roughly between 20 Hz and 20,000 Hz (20 kHz). Below 20 Hz the sound is infrasonic and above 20,000 Hz it is ultrasonic — both are inaudible to us. (This upper limit falls with age.)

Why the others are wrong

(b)80 Hz – 100 Hz — Far too narrow — humans easily hear frequencies well below 80 Hz and far above 100 Hz. This is only a tiny slice of the true range.
(c)2 lac Hz – 4 lac Hz — '2 lac to 4 lac Hz' (200,000–400,000 Hz) is deep in the ultrasonic range used by bats and dolphins — far beyond human hearing.
(d)0 Hz – 20 Hz — This is the infrasonic range (below 20 Hz), which the human ear cannot perceive as sound.

Concept

Sound is classified by frequency. Infrasonic: below 20 Hz (felt, not heard — e.g. earthquakes). Audible: about 20 Hz to 20,000 Hz — the human hearing range. Ultrasonic: above 20,000 Hz — used by bats and dolphins for echolocation and in medical ultrasound. Frequency is measured in hertz (Hz), where 1 Hz = one vibration per second.

The question hides the trap in units. Option C uses 'lac' (lakh = 100,000 in the Indian system), so '2 lac–4 lac Hz' is ultrasonic. Remember the neat band 20 Hz to 20 kHz for humans, and everything below is infrasound, everything above is ultrasound.

Key facts

Human audible range: about 20 Hz to 20,000 Hz (20 kHz).
Below 20 Hz = infrasonic; above 20,000 Hz = ultrasonic.
Frequency unit is the hertz (Hz) = vibrations per second; 1 lakh = 100,000.
The upper hearing limit decreases with age and noise exposure.

Sound by frequency: where human hearing sits

Infrasonic→below 20 Hz — inaudible (e.g. earthquakes)

Audible (human hearing)→20 Hz – 20,000 Hz

Ultrasonic→above 20,000 Hz — bats, dolphins, medical ultrasound

Humans hear only the middle band, 20 Hz to 20 kHz.

Study next

Ultrasound and its uses (medical imaging, SONAR, cleaning)Infrasound and sources (earthquakes, large animals)Properties of sound waves: frequency, wavelength, amplitude, pitchEcholocation in bats and dolphinsSpeed of sound in different media

Common traps

Misreading 'lac' (lakh) and picking the ultrasonic 2–4 lac Hz option
Confusing the audible band with the infrasonic (0–20 Hz) range

Asked directly ('audible range of humans') or via the infrasonic/ultrasonic boundaries. Fix the numbers: 20 Hz and 20,000 Hz.

Related PYQs

No directly related past PYQ was found.

Practice

practice — not a real PYQ
Sound of frequency above 20,000 Hz, inaudible to humans, is called:
- (a)infrasonic
- (b)ultrasonic
- (c)supersonic
- (d)audible
Answer(b) ultrasonic — 'supersonic' refers to speed faster than sound, not frequency.
practice — not a real PYQ
Which animal is well known for using ultrasonic sound (echolocation) beyond the human hearing range?
- (a)Elephant
- (b)Bat
- (c)Cow
- (d)Sparrow
Answer(b) Bat — it navigates and hunts using ultrasonic echolocation.