Radio waves belongs to the class of waves whose velocity is about

1. Analyze the question

The question asks for the velocity of radio waves. In physics, radio waves are a specific type of wave within the electromagnetic spectrum. To answer this, we need to identify the speed at which all electromagnetic waves travel through a vacuum.

2. Explain the concept

Radio waves, along with light, X-rays, microwaves, and gamma rays, are electromagnetic waves. A fundamental principle in physics is that all electromagnetic waves travel at the same constant speed in a vacuum (or approximately the same speed in air). This speed is known as the speed of light, denoted by the symbol $c$.

The value of this constant is approximately $300,000,000$ meters per second, which is written in standard form as $3 \times 10^8 \text{ m/s}$.

3. Show the solution

• Step 1: Identify the nature of the wave. Radio waves are electromagnetic waves.
• Step 2: Recall the speed of electromagnetic waves. The speed of electromagnetic waves in a vacuum is a universal constant: $c \approx 3 \times 10^8 \text{ m/s}$.
• Step 3: Compare this with the given options: • A: $340 \text{ m/s}$ is the approximate speed of sound in air. • B: $3 \times 10^6 \text{ m/s}$ is incorrect. • C: $3 \times 10^8 \text{ m/s}$ matches the speed of light. • D: $3 \times 10^{-8} \text{ m/s}$ is an extremely slow speed, not applicable here.

4. Identify the answer

The correct option is C.

5. Exam Tip

Remember the acronym "R-M-I-V-U-X-G" for the electromagnetic spectrum (Radio, Microwave, Infrared, Visible light, Ultraviolet, X-ray, Gamma ray). All of these travel at the speed of light ($3 \times 10^8 \text{ m/s}$). Do not confuse this with the speed of sound ($340 \text{ m/s}$), which is much slower and requires a medium to travel!