Two waves having equations \[{{x}_{1}}=a\sin (\omega \,t+{{\varphi }_{1}})\], \[{{x}_{2}}=a\sin \,(\omega \,t+{{\varphi }_{2}})\] If in the resultant wave the frequency and amplitude remain equal to those of superimposing waves. Then phase difference between them is [CBSE PMT 2001]

• A.            \[\frac{\pi }{6}\]                 
• B.            \[\frac{2\pi }{3}\]
• C.            \[\frac{\pi }{4}\]                 
• D.            \[\frac{\pi }{3}\]