A) \[2\,\,\pi \]
B) \[4\,\,\pi \]
C) \[6\,\,\pi \]
D) \[8\,\,\pi \]
Correct Answer: C
Solution :
Given, \[y=2\cos \,(20\pi t-2\pi \times 0.008\,x+0.7\pi )\] Comparing with general equation \[y=a\,\cos \,(\omega \,t\pm kx\pm {{\phi }_{0}})\] we get \[k=2\pi \times 0.008\] \[\frac{2\pi }{\lambda }=2\pi \times 0.008\] \[\left[ As\,\,k=\frac{2\pi }{\lambda } \right]\] \[\Rightarrow \] \[\lambda =\frac{1}{0.008}\] \[\lambda =125\,\,cm\] = 1.25 m Now, phase difference \[(\Delta \phi )\] \[=\frac{2\pi }{\lambda }\times \] path difference \[(\Delta x)\] \[=\frac{2\pi }{1.25}\times 4=6\pi \]
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