Answer the following questions:
$(a)$ When a low flying aircraft passes overhead,we sometimes notice a slight shaking of the picture on our $TV$ screen. Suggest a possible explanation.
$(b)$ As you have learnt in the text,the principle of linear superposition of wave displacement is basic to understanding intensity distributions in diffraction and interference patterns. What is the justification of this principle?

(N/A) Weak radar signals sent by a low flying aircraft can interfere with the $TV$ signals received by the antenna. As a result,the $TV$ signals may get distorted. Hence,when a low flying aircraft passes overhead,we sometimes notice a slight shaking of the picture on our $TV$ screen.
$(b)$ The principle of linear superposition of wave displacement is essential to our understanding of intensity distributions and interference patterns. This is because superposition follows from the linear character of the differential equation that governs wave motion. If $y_{1}$ and $y_{2}$ are the solutions of the second-order wave equation,then any linear combination of $y_{1}$ and $y_{2}$ will also be a solution of the wave equation.