Question

If two waves of same frequency and same amplitude, on superposition, produce a resultant disturbance of the same amplitude, the wave differ in phase by

• A. $\pi$
• B. $2\pi /3$
• C. $zero$
• D. $\pi /3$

Answer 1

Answer: (B)

$2\pi /3$

We know that:

$R^2=a^2+b^2+2abcos\varphi$
$\therefore a^2=a^2+a^2+2a^{2}cos\varphi$

$\Rightarrow cos\varphi =-\frac{1}{2}$

$\Rightarrow \varphi =\frac{2\pi }{3}$