Question

A source of sound gives five beats per second when sounded with another source of frequency $100\, s ^{-1}$. The second harmonic of the source together with a source of frequency $205\, s ^{-1}$ gives five beats per second. What is the frequency of the source?

• A. $105\, s ^{-1}$
• B. $205\, s ^{-1}$
• C. $95\, s ^{-1}$
• D. $100\, s ^{-1}$

Answer 1

Answer: (A)

Frequency of the source $=100 \pm 5=105\, Hz$ or $95\, Hz$
Second harmonic of the source $=210\, Hz$ or $190\, Hz$.
As the second harmonic gives 5 beats/sec with sound of frequency $205\, Hz$, the second harmonic should be $210\, Hz$.
$\Rightarrow $ Frequency of the source $=105\, Hz$