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

Options

A. interference
B. diffraction
C. polarisation of direct signal
D. Both (b) and (c)

Explanation

### Step-by-Step Solution

**(a)** When a low flying aircraft passes overhead, we sometimes notice a slight shaking of the picture on our TV screen. A possible explanation for this phenomenon involves the interference of electromagnetic signals.

1. **Understanding the Source of Signals**: Aircraft typically use radar signals for navigation and communication. These signals are electromagnetic waves that can interfere with other electromagnetic signals, such as those used for television broadcasting.

2. **Interference of Signals**: When the aircraft is flying overhead, its radar signals can overlap with the TV signals. This overlap leads to a phenomenon known as interference, where two or more waves superpose to form a resultant wave.

3. **Resultant Distortion**: The interference can cause variations in the amplitude and frequency of the TV signals. This results in a distortion of the picture on the TV screen, which manifests as a slight shaking or flickering.

4. **Conclusion**: Thus, the shaking of the TV picture can be attributed to the interference between the radar signals from the aircraft and the TV signals, causing temporary distortions.

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**(b)** The principle of linear superposition of wave displacement is fundamental to understanding intensity distributions in diffraction and interference patterns.

1. **Definition of Superposition**: The principle of superposition states that when two or more waves overlap, the resultant displacement at any point is the sum of the displacements due to each wave individually.

2. **Linear Nature of Waves**: This principle is justified because it holds true for linear systems, where the response (displacement) is directly proportional to the input (wave). This linearity is a characteristic of the differential equations governing wave motion.

3. **Amplitude and Intensity Relationship**: When waves superpose, the resultant amplitude can be calculated. Since intensity is proportional to the square of the amplitude (I ∝ A²), knowing the resultant amplitude allows us to determine the intensity distribution.

4. **Application in Wave Motion**: The linear superposition principle is essential for analyzing interference and diffraction patterns because it allows us to predict how waves will combine and what the resulting intensity distribution will be.

5. **Conclusion**: Therefore, the justification for the principle of linear superposition lies in its ability to describe the behavior of waves in a linear medium, leading to predictable outcomes in terms of amplitude and intensity.

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