Which type of electromagnetic wave is used in long-distance communications and passes through walls?

Which type of electromagnetic wave is used in long-distance communications and passes through walls?

• A. Infrared
• B. Ultraviolet
• C. Radio
• D. Gamma rays

Answer: (C)

Understanding how electromagnetic waves propagate through space and obstacles is what this question tests. For long‑distance communications, you want waves that travel far and can get through barriers. Radio waves have the longest wavelengths used for communication, so they can cover long distances and pass through walls with only moderate attenuation. Infrared waves don’t pass through walls well; they’re absorbed or reflected by most materials, so they’re suited to short‑range, line‑of‑sight applications. Ultraviolet waves are largely blocked by the atmosphere and materials under normal conditions, and they’re not used for practical long‑distance communications. Gamma rays, while highly penetrating, are dangerous and require heavy shielding, making them unsuitable for everyday communication. So the correct type is radio waves.

Understanding how electromagnetic waves propagate through space and obstacles is what this question tests. For long‑distance communications, you want waves that travel far and can get through barriers. Radio waves have the longest wavelengths used for communication, so they can cover long distances and pass through walls with only moderate attenuation. Infrared waves don’t pass through walls well; they’re absorbed or reflected by most materials, so they’re suited to short‑range, line‑of‑sight applications. Ultraviolet waves are largely blocked by the atmosphere and materials under normal conditions, and they’re not used for practical long‑distance communications. Gamma rays, while highly penetrating, are dangerous and require heavy shielding, making them unsuitable for everyday communication. So the correct type is radio waves.