Question

Two identical wave pulses are formed as shown in the figure. If the first pulse undergoes a reflection from the wall, then the net amplitude of the interference between the second pulse and the first reflected pulse is -

• A. $0\text{cm}$
• B. $2\text{cm}$
• C. $1.5\text{cm}$
• D. $1\text{cm}$

Answer 1

The correct option is A $0\text{cm}$

Before reflection -


After reflection -


The second pulse and the first reflected pulse are out of phase by ${180}^{\circ }$, so phase difference, $\varphi ={180}^{\circ }$.

Now, the resultant amplitude,

$A_{\text{net}}=\sqrt{A_1^2+A_2^2+2A_1{A}_2\cos \varphi }$

$\Rightarrow A_{\text{net}}=\sqrt{1^2+1^2+2\left(1\right)\left(1\right)\cos {180}^{\circ }}$

$\Rightarrow A_{\text{net}}=0\text{cm}$

Hence, option $\left(A\right)$ is the correct answer.