Compared to audible sound waves, ultrasound waves have
- (a)higher speed.
- (b)higher frequency.
- (c)longer wavelength.
- (d)both higher speed and frequency.
Correct — B, higher frequency. Ultrasound is sound above the human hearing range, i.e. frequency greater than 20,000 Hz (audible sound spans 20 Hz to 20 kHz). Its defining feature is a higher frequency. The speed of a sound wave depends on the medium, not on frequency, so ultrasound travels at the same speed as audible sound in a given medium; and from v = f x lambda, its higher frequency gives it a SHORTER, not longer, wavelength.
- (a)higher speed. — The speed of sound depends on the medium (and its temperature), not on frequency. In the same medium ultrasound and audible sound travel at the same speed, so 'higher speed' is wrong.
- (c)longer wavelength. — From v = f x lambda, at the same speed a higher frequency means a SHORTER wavelength. Ultrasound's short wavelength is what makes it useful for fine imaging (sonography), so 'longer wavelength' is the opposite of the truth.
- (d)both higher speed and frequency. — The frequency is higher, but the speed is NOT - speed is fixed by the medium. So only the frequency is higher, which makes this option half wrong.
Ultrasound (ultrasonic) waves are sound waves with frequency above 20,000 Hz, beyond the upper limit of human hearing. Since the speed of sound depends only on the medium, ultrasound travels at the same speed as audible sound in that medium, and because v = f x lambda, its higher frequency means a shorter wavelength.
The single distinguishing property of ultrasound is its frequency (above 20 kHz). Rule out speed - that is a property of the medium, not the wave's frequency. Rule out longer wavelength - the wave equation makes wavelength shorter when frequency rises. That leaves 'higher frequency' as the only correct choice.
- Human audible range: 20 Hz to 20,000 Hz; ultrasound is above 20,000 Hz, infrasound below 20 Hz.
- The speed of a wave depends on the medium; v = f x lambda.
- Higher frequency implies shorter wavelength (at constant speed).
- Ultrasound uses: sonography (medical imaging), SONAR, cleaning and flaw detection; bats and dolphins use it too.
Ultrasound differs by having a higher frequency; its speed equals that of audible sound in the same medium.
- Thinking higher frequency means higher speed - speed depends on the medium, not on frequency.
- Forgetting the inverse frequency-wavelength relation (higher frequency means shorter wavelength).
Ultrasound is asked via its defining property (frequency above 20 kHz) or through v = f x lambda reasoning about wavelength and speed.
No directly related past PYQ was found.
- practice — not a real PYQ
The audible range of frequency for a normal human being is
- (a)2 to 20 Hz
- (b)20 to 20,000 Hz
- (c)20,000 to 40,000 Hz
- (d)1 to 10 Hz
Answer(b) 20 to 20,000 Hz - sound above this range is ultrasound.
- practice — not a real PYQ
If the frequency of a wave increases while its speed stays constant, its wavelength
- (a)increases
- (b)decreases
- (c)stays the same
- (d)becomes zero
Answer(b) decreases - from v = f x lambda, wavelength is inversely proportional to frequency.