Two sound waves (expressed in CGS units) given by \[{{y}_{1}}=0.3\sin \frac{2\pi }{\lambda }(vt-x)\] and \[{{y}_{2}}=0.4\sin \frac{2\pi }{\lambda }(vt-x+\theta )\] interfere. The resultant amplitude at a place where phase difference is \[\pi /2\] will be [MP PET 1991]

• A.            0.7 cm                                     
• B.            0.1 cm
• C.            0.5 cm                                     
• D.            \[\frac{1}{10}\sqrt{7}\,cm\]