Navedtra 144182, Neets, Module 10

Radio waves are a form of electromagnetic radiation that cannot be felt through sight, touch, or hearing. They are invisible and do not have any physical sensation associated with them. Therefore, the correct answer is "none of the above" as none of our senses can directly perceive radio waves.

Radio waves travel at the speed of light because they are a form of electromagnetic radiation. Electromagnetic waves, including radio waves, travel through space at a constant speed of approximately 299,792,458 meters per second, which is the speed of light in a vacuum. This speed is a fundamental constant in physics and is the fastest speed at which any information or energy can travel in the universe. Therefore, radio waves, being a type of electromagnetic wave, also travel at the speed of light.

Diffraction is the correct principle of wave propagation that explains the reception of an AM-band radio signal over mountains. Diffraction occurs when a wave encounters an obstacle or passes through a narrow opening, causing it to bend and spread out. In the case of radio signals, when they encounter mountains, they diffract around them, allowing the signal to reach areas that are blocked by the mountains. This is why AM-band radio signals can be received even when there are obstacles like mountains in the way. Refraction, on the other hand, refers to the bending of waves when they pass from one medium to another, which is not relevant in this context.

The major advantage of telegraph over earlier methods is its range. Unlike previous communication methods that were limited to short distances, the telegraph allowed messages to be transmitted over long distances using electrical signals. This significantly expanded the reach and effectiveness of communication, making it possible to send messages across vast distances almost instantaneously.