#sound

Doppler Effect

Two waves of frequencies 510 Hz and 514 Hz interfere. How many beats are heard in 15 seconds?

**Frequency shift** proportional to source speed relative to wave speed v. Understanding sign convention for approaching versus receding is key, with approaching increasing frequency and receding decreasing, central to Doppler applications. Beat frequency: vbₑₐt = 514 - 510 = 4 Hz . Beats in 15 s: 4 × 15 = 60 . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 60, illustrating frequency-length-speed interdependence and quantization by boundaries. This aligns with NCERT Class 11 treatment, emphasizing conservation, symmetry and dimensional consis

Ref: NCERT > Physics Book > Waves > Doppler Effect

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Vibrations of Air Columns - Open and Closed Pipes

A pipe closed at one end has a length of 0.45 m and a speed of sound of 360 m/s. What is the frequency of its fifth harm

**Resonance in pipes** occurs when length accommodates standing wave pattern. Closed pipe L = (2n-1)λ/4, so f₁ = v/(4L). Given f₁ and v, length follows L = v/(4f₁), enabling length calculation from measured resonance frequency and sound speed 330-340 m/s. For closed pipe: v_n = (n + (1/2)) (v/2L) , n = 4 for fifth harmonic. v₄ = (4 + (1/2)) (360/2 × 0.45) = 4.5 × (360/0.9) = 4.5 × 400 = 1800 Hz . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 1800 Hz, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Vibrations of Air Columns - Open and Closed Pipes

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Vibrations of Air Columns - Open and Closed Pipes

A pipe open at both ends has a length of 0.425 m and resonates with a source of frequency 800 Hz. What is the harmonic n

**Air column vibrations** depend on end conditions. Pipe closed at one end has displacement node at closed end and antinode at open, allowing only odd harmonics, fundamental f₁ = v/(4L). Open pipe has antinodes at both ends, fₙ = n·v/(2L), all harmonics present, v sound speed. v_n = (n v/2L) . 800 = (n × 340/2 × 0.425) = (n × 340/0.85) . 800 = n × 400 ⇒ n = (800/400) = 2 . Second harmonic. Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 2, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Vibrations of Air Columns - Open and Closed Pipes

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PHYSICS

Which wave property is most affected when a sound wave encounters a change in the medium’s temperature?

Speed of sound in a gas increases with temperature ( v propto sqrtT ), significantly altering its propagation, while frequency remains source-dependent and amplitude may vary less directly.

Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Oscillations and Waves, Topic: SHM, wave motion and superposition.

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