question_answer

Two adjacent piano keys are struck simultaneously. The notes emitted by them have frequencies \[{{n}_{1}}\] and \[{{n}_{2}}\]. The number of beats heard per second is [CPMT 1974, 78; CBSE PMT 1993]

A)            \[\frac{1}{2}({{n}_{1}}-{{n}_{2}})\]                                 

B)            \[\frac{1}{2}({{n}_{1}}+{{n}_{2}})\]

C)            \[{{n}_{1}}\tilde{\ }{{n}_{2}}\]                                          

D)            \[2\,({{n}_{1}}-{{n}_{2}})\]