Frequency, Pitch and Ultrasonic Waves
~8 min read
- Audible range: 20 Hz to 20,000 Hz (20 kHz). Below 20 Hz = infrasonic; above 20 kHz = ultrasonic.
- Pitch & loudness: Pitch determined by frequency; loudness by amplitude. Quality (timbre) by waveform.
- Ultrasonic uses: SONAR, sonography, ultrasonic cleaning, breaking kidney stones, non-destructive testing of metals.
Frequency tells the ear what note it hears. CDS/OTA tests audible range, distinction between pitch/loudness/quality, and ultrasonic applications in medicine and industry.
Audible Range and Beyond
| Range | Frequency | Heard by |
|---|---|---|
| Infrasonic | Below 20 Hz | Elephants, whales (sensed by humans only as vibration) |
| Audible (human) | 20 Hz - 20,000 Hz | Healthy young humans |
| Ultrasonic | Above 20 kHz | Bats (up to 200 kHz), dolphins, dogs (up to 45 kHz) |
Pitch, Loudness and Quality
- Pitch — sensation that distinguishes a high note from a low one. Depends on frequency.
- Loudness — magnitude of sound sensation. Depends on amplitude (and ear's logarithmic response). Measured in decibel (dB).
- Quality (timbre) — feature that lets us distinguish a violin from a flute playing the same note. Determined by the waveform (harmonics present).
Ultrasonic Applications
- SONAR — underwater navigation, depth-finding, locating submarines, fish shoals.
- Ultrasonography — medical imaging of foetus, internal organs (non-ionising, safer than X-rays).
- Lithotripsy — breaking kidney stones without surgery.
- Ultrasonic cleaning — jewellery, surgical instruments, watches.
- Non-destructive testing — detect flaws and cracks in metal castings, weld joints, rails.
- Echolocation — bats and dolphins use ultrasonic pulses to map surroundings.
CDS/OTA PYQ Examples
Q: Audible range of frequency for humans is:
(a) 2 - 200 Hz (b) 20 - 20,000 Hz (c) 200 - 200,000 Hz (d) 20 - 200 Hz
Answer: (b) 20 Hz to 20 kHz.
Q: Pitch of a sound depends on:
(a) Amplitude (b) Frequency (c) Wavelength alone (d) Speed
Answer: (b) Frequency — higher frequency means higher pitch.
Q: Sound used in medical sonography is:
(a) Infrasonic (b) Audible (c) Ultrasonic (d) Supersonic
Answer: (c) Ultrasonic — typically 2-15 MHz.
Q: Loudness of sound is measured in:
(a) Hertz (b) Decibel (c) Watt (d) Newton
Answer: (b) Decibel (dB).
Drill Frequency, Pitch and Ultrasonic Waves for CDS/OTA
CDS/OTA-pattern items on Frequency, Pitch and Ultrasonic Waves with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
Why is ultrasonic preferred over audible sound for SONAR?
Higher frequency means shorter wavelength and tighter directional beam, giving better resolution and less ambient interference.
What is the difference between ultrasonic and supersonic?
Ultrasonic — sound above the human audible range. Supersonic — speed greater than the speed of sound (a property of motion, not sound itself).
Why can elephants and whales communicate over very long distances?
They use low-frequency infrasonic waves, which travel further with less absorption through air or water.