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Television (TV) transmission works by sending electromagnetic waves, specifically radio waves, from a transmitting antenna to receiving antennas. These waves typically travel in straight lines rather than bending around obstacles or following the curvature of the Earth. Because of this, TV signals cannot cover very large areas directly, and the main reason is that the Earth is spherical in shape.
TV broadcasting uses very high frequency (VHF) or ultra-high frequency (UHF) waves. These waves are classified as space waves that propagate in a line-of-sight path. When these waves travel far enough, the Earth's curved surface eventually obstructs the signal path, preventing it from reaching receivers beyond the horizon. This limitation is not due to weak wave strength (Option 1) or poor picture quality (Option 2), but because of geometrical obstruction caused by Earth's curvature.
Option 4, stating that air is not a good conductor, is incorrect because TV waves are electromagnetic and do not need a conducting medium; they can travel through air and even space effectively.
To overcome this limitation, relay stations, satellites, and cable networks are used to retransmit signals to areas that cannot directly receive the broadcast from the main transmission station. Satellites orbit high above the Earth and can beam signals over a much larger portion of the globe, solving the issue caused by the planet’s spherical shape.
Hence, the correct answer is Option 3: The shape of the Earth is spherical, as this is the primary factor restricting the coverage area of TV transmissions.
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