Ultrasound Applications in Everyday and Medical Contexts

Steps:

• Ultrasound refers to sound waves above 20 kHz, used where high-frequency vibrations are beneficial.
• P (cleaning jewellery): Correct, as ultrasonic cleaners use cavitation from sound waves to remove dirt.
• Q (tanning a sunbed): Incorrect, as sunbeds use ultraviolet light for skin tanning, not sound waves.
• R (obtaining an image of an unborn baby): Correct, as ultrasound imaging (sonography) visualizes fetuses safely via echoes.

Why B is correct:

• Ultrasound's piezoelectric effect generates echoes for cleaning via vibrations and imaging via reflections, matching P and R per wave physics principles.

Why the others are wrong:

• A includes Q, which misapplies ultrasound to UV-based tanning.
• C includes Q and excludes valid P cleaning use.
• D includes incorrect Q alongside P and R.

Final answer: B