The equation of a stationary wave is given by
$y = 6 \sin \left(\frac{\mathrm{\pi x}}{3}\right) \cos 40 \mathrm{\pi t}$
where y and x are given in cm and time t in second, then the phase difference between two points on opposite sides of an antinode with a separation of I cm between them is:

• A

  zero radian

• B

  $\left(\frac{\mathrm{\pi }}{3}\right) \mathrm{radian}$

• C

  $\left(\frac{\mathrm{\pi }}{2}\right) \mathrm{radian}$

• D

  $\mathrm{\pi } \mathrm{radian}$