Explanation:
SONAR (Sound Navigation and Ranging) uses ultrasonic waves (frequency > 20 kHz) because they have high directionality, short wavelength for better resolution, and minimal absorption in water. Radio waves attenuate rapidly in water; infrasonic waves have long wavelengths unsuitable for detection; light doesn't propagate far in water. Memory tip: 'Ultra = beyond human hearing; used in SONAR/ultrasound imaging'. This application question tests knowledge of wave frequency ranges and their practical uses, common in competitive exams linking physics to technology. Always recall frequency thresholds: infrasonic 20kHz.
Explanation:
Least count of screw gauge = Pitch / Number of circular scale divisions. Given pitch = 1 mm, divisions = 100, so LC = 1 mm / 100 = 0.01 mm. This represents the smallest measurement the instrument can accurately detect. Screw gauges measure small dimensions like wire diameter with high precision. Memory tip: Least count formula is universal for vernier and screw instruments: value per division on main scale divided by total circular divisions. This concept is frequently tested in practical physics sections of competitive exams.
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