Question

A source of sound of frequency $256\, Hz$ is moving towards a wall with a velocity of 5m/s. Velocity of sound is $330$ m/s. The number of beats heard by an observer standing behind the source is nearly -

• A. $\frac{256 \times 330}{325}-256$
• B. $256-\frac{256 \times 330}{335}$
• C. $\frac{256 \times 330}{325}-\frac{256 \times 330}{335}$
• D. $\frac{256 \times 330}{325}-\frac{256 \times 330}{325}$

Answer 1

Answer: (C)

$n _{ D }=256\left(\frac{330}{330+5}\right)$
$n _{ R }=256\left(\frac{330}{330-5}\right)$
$\Delta n = n _{ R }- n _{ D }=\frac{256 \times 330}{325}$
$-\frac{256 \times 330}{335}$