Practice question

**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. At rigid boundary, phase changes by π . Incident: y_i = 0.05 sin (12x - 36t) . Reflected: y_r = -0.05 sin (12x + 36t) . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields y = -0.05 sin (12x + 36t), illustrating frequency-length-speed interdependence and quantization by boundaries.