Coil center magnetic field B = μ₀NI/(2R). If N doubled, B becomes:
A. Four times
B. Half
C. Same
D. Double
Answer: Option D
Solution (By JKSSB Mock Tests)
B ∝ N. Double turns ⇒ double field at center. Direct proportionality from Biot-Savart law. Memory tip: 'Coil field: B ∝ NI; more turns ⇒ stronger field'. Magnetism formula frequently tested in competitive exams.
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.
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