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#acoustic physics

3 public questions tagged with this topic.

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

**Doppler effect** describes apparent frequency shift due to relative motion between source and observer, f' = f·v/(v ∓ v_s) for source motion, f' = f·(v ± v_o)/v for observer motion, upper signs for approach increasing observed frequency. Motion towards observer compresses wavelength raising f'. Speed of sound in a gas increases with temperature ( v ∝ √(T) ), significantly altering its propagation, while frequency remains source-dependent and amplitude may vary less directly. Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields Speed, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Doppler Effect

A steel rod of length 1.8 m has a fundamental frequency of longitudinal vibrations of 1.5 kHz. What is the speed of soun

**Longitudinal vibrations in rods** clamped at middle have fundamental with node at clamp and antinodes at ends, f₁ = v/(2L), v speed of sound in material (m/s). This relation allows v extraction from measured f₁ and length L, e.g., v = 2L·f₁. For rod clamped at middle, fundamental: v₁ = (v/2L) . 1500 = (v/2 × 1.8) ⇒ v = 1500 × 3.6 = 5400 m/s . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 5400 m/s, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Sound Waves, Reflection and Characteristics

A steel rod of length 1.2 m has a fundamental frequency of longitudinal vibrations of 2.5 kHz. What is the speed of soun

**Sound wave reflection** at rigid wall behaves like string fixed end, displacement inverted. Equation of reflected wave includes sign change and direction reversal, amplitude unchanged but sign may flip, explaining standing wave formation with incident wave. For rod clamped at middle, fundamental: v₁ = (v/2L) . 2500 = (v/2 × 1.2) ⇒ v = 2500 × 2.4 = 6000 m/s . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 6000 m/s, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Sound Waves, Reflection and Characteristics