The phenomenon of beats can be observed when two sound waves have:
A. Slightly different frequencies
B. Same frequency but different amplitudes
C. Very different frequencies
D. Same frequency and amplitude
Answer: Option A
Solution (By JKSSB Mock Tests)
Beats occur due to interference of two waves with slightly different frequencies (Δf small, typically < 10 Hz for audible beats). The beat frequency is |f₁ - f₂|, causing periodic loudness variation. Same frequency (A, B) produces steady interference (no beats); very different frequencies (D) produce rapid fluctuations not perceived as beats. Memory aid: 'Beats: |f₁ - f₂| small ⇒ audible pulsations; used in tuning'. This wave phenomenon question tests superposition understanding, frequently examined in competitive exams. Always link beat perception to frequency difference magnitude; competitive exams often test qualitative conditions for observable beats.
Explanation:
Coefficient of performance (COP) for refrigerator: COP = Q₂ / W, where Q₂ is heat extracted from cold reservoir, W is work input. By energy conservation, Q₁ = Q₂ + W (heat rejected to hot reservoir). COP > 1 typically. Option A is inverse; C and D relate to heat engine efficiency. Memory aid: 'Refrigerator COP = desired output (cooling) / work input'. This thermodynamics definition is frequently tested in competitive exams. Always distinguish refrigerator COP (cooling effect per work) from heat engine efficiency (work output per heat input).
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