When a low flying aeroplane passes over head, we sometimes notice a slight shaking of the picture on our TV screen. This is due to

Options

A. diffraction of the signal received from the antenna.
B. interference of the direct signal received by the antenna with the weak signal reflected by the passing aircraft.
C. change of magnetic flux occurring due to the passage of aircraft.
D. vibrations created by the passage of aircraft.

Answer

To solve the question about why a low-flying airplane causes a slight shaking of the picture on a TV screen, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Scenario**: When a low-flying airplane passes overhead, it can affect the signals received by the TV antenna. This is important to note as it sets the context for the interference that occurs.

2. **Signal Reception**: The TV antenna receives signals that are transmitted from broadcasting stations. These signals can be direct signals (coming straight from the transmitter) and reflected signals (bouncing off surfaces like buildings or the ground).

3. **Interference**: As the airplane flies overhead, it can cause changes in the path of the signals. The direct signal from the transmitter may interfere with the reflected signals that are also being received by the antenna. This interference can lead to variations in the signal strength.

4. **Amplitude Variation**: The interference between the direct and reflected signals causes fluctuations in the amplitude of the received signal. This is because the two signals can constructively or destructively interfere with each other, leading to changes in the overall signal strength.

5. **Effect on TV Picture**: The TV screen displays images based on the strength and quality of the received signal. When the amplitude of the signal varies due to interference, it can cause the picture to shake or flicker. This is perceived as a slight shaking of the picture on the TV screen.

6. **Conclusion**: Therefore, the shaking of the picture on the TV screen when a low-flying airplane passes overhead is due to the interference of the direct signal received by the antenna with the reflected signal, which causes variations in the amplitude of the signal.

### Final Answer:
The shaking of the picture on the TV screen is due to the interference of the direct signal received by the antenna with the reflected signal caused by the low-flying airplane.

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