Which of the following pairs is part of the electromagnetic spectrum?  I. Radio waves II. sound waves III. Gamma rays IV. water waves

Analysis

To solve this question, we need to identify which of the listed waves belong to the electromagnetic (EM) spectrum. The electromagnetic spectrum consists of waves that do not require a material medium for propagation and travel at the speed of light ($3 \times 10^8 \text{ m/s}$) in a vacuum.

Concept Explanation

The electromagnetic spectrum includes the following, in order of increasing frequency:

1. Radio waves
2. Microwaves
3. Infrared radiation
4. Visible light
5. Ultraviolet radiation
6. X-rays
7. Gamma rays

Why the others are excluded:

• Sound waves: These are mechanical waves. They require a material medium (solid, liquid, or gas) to travel and cannot propagate through a vacuum.
• Water waves: These are also mechanical waves that require a medium (water) to propagate.

Step-by-Step Solution

1. Evaluate I (Radio waves): Radio waves are part of the electromagnetic spectrum. (Correct)
2. Evaluate II (Sound waves): Sound waves are mechanical, longitudinal waves, not electromagnetic. (Incorrect)
3. Evaluate III (Gamma rays): Gamma rays are high-frequency electromagnetic waves. (Correct)
4. Evaluate IV (Water waves): Water waves are mechanical surface waves. (Incorrect)

Comparing our findings with the options:

• I and III are the correct components. This corresponds to option C.

Exam Tip

Remember the mnemonic "Raging Martians Invaded Venus Using X-ray Guns" to recall the order of the electromagnetic spectrum:

• Radio waves
• Microwaves
• Infrared
• Visible light
• Ultraviolet
• X-rays
• Gamma rays