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Ultrasound Applications — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Ultrasound Applications MCQs with step-by-step solutions (10 questions). Part of Sound. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Ultrasound Applications · medium · theory
Ultrasound consists of sound waves of frequency:
A. below 20 Hz
B. above 20,000 Hz ✓ Correct
C. between 20 Hz and 20,000 Hz
D. exactly 20,000 Hz
Solution: Ultrasound is sound above the human audible limit of 20 kHz.
Q2 — Ultrasound Applications · medium · theory
The technique used by ships to find the depth of the sea using ultrasound is called:
A. LASER
B. MRI
C. SONAR ✓ Correct
D. RADAR
Solution: SONAR (Sound Navigation And Ranging) uses ultrasound echoes to measure depth and detect objects underwater.
Q3 — Ultrasound Applications · hard · theory
Ultrasound is used to detect cracks inside metal blocks because it:
A. melts the metal
B. is audible to workers
C. passes straight through cracks unchanged
D. is reflected back from a crack (a change in medium) ✓ Correct
Solution: A crack is a gap that reflects the ultrasound, revealing the flaw that a solid block would not.
Q4 — Ultrasound Applications · medium · theory
In hospitals, ultrasound is commonly used to:
A. sterilise the whole body
B. image internal organs and a developing foetus (ultrasonography) ✓ Correct
C. treat fractures by heating
D. measure body temperature
Solution: Ultrasonography forms images of internal organs and the foetus using reflected ultrasound.
Q5 — Ultrasound Applications · medium · theory
Ultrasonic waves are used to clean spiral tubes and delicate machine parts because they can:
A. produce loud audible sound
B. dislodge dirt particles from hard-to-reach places by vibration ✓ Correct
C. dissolve all metals
D. generate electricity
Solution: High-frequency vibrations shake off dirt from otherwise inaccessible surfaces.
Q6 — Ultrasound Applications · hard · theory
Bats and dolphins navigate and locate prey mainly using:
A. infrasound only
B. their sense of smell
C. visible light
D. ultrasound echoes (echolocation) ✓ Correct
Solution: They emit ultrasonic pulses and interpret the echoes to locate obstacles and prey — echolocation.
Q7 — Ultrasound Applications · easy · theory
Ultrasound is the name given to sound whose frequency is
A. above 20,000 Hz ✓ Correct
B. exactly 20 Hz
C. between 20 Hz and 20,000 Hz
D. below 20 Hz
Solution: Ultrasound has frequencies above 20,000 Hz, which is beyond the upper limit of human hearing. Sound below 20 Hz is called infrasound.
Q8 — Ultrasound Applications · medium · theory
Which of the following is NOT a common use of ultrasound?
A. Detecting hidden cracks in metal blocks
B. Cleaning delicate machine parts and jewellery
C. Imaging an unborn baby in the womb (sonography)
D. Cooling down a hot object quickly ✓ Correct
Solution: Ultrasound is widely used for cleaning, medical imaging and flaw detection in metals. It does not cool objects, so cooling a hot object is not an application of ultrasound.
Q9 — Ultrasound Applications · medium · numerical
A SONAR device on a ship sends an ultrasound pulse straight down and receives its echo from the seabed after 4 s. If the speed of sound in seawater is 1500 m/s, how deep is the sea?
A. 1500 m
B. 750 m
C. 6000 m
D. 3000 m ✓ Correct
Solution: In 4 s the pulse travels down and back: total distance = 1500 x 4 = 6000 m. The depth is half of this, 6000 / 2 = 3000 m.
Q10 — Ultrasound Applications · hard · theory
Ultrasound is preferred over ordinary audible sound for medical imaging and for detecting tiny flaws inside metals mainly because
A. it does not need any medium to travel through
B. it travels faster than audible sound in every medium
C. it can have a higher frequency and shorter wavelength, giving sharper detail and better directionality ✓ Correct
D. it is much louder and so can be heard clearly
Solution: Its high frequency means a short wavelength, so ultrasound can travel in a narrow directed beam and resolve very small features. This sharp detail and straight-line travel is what makes it ideal for scanning bodies and finding hidden cracks.