Question: Which of the following is also referred to as 'heat waves'?

Step 1 (Foundational Concept): [0.5 Mark]

According to the Electromagnetic Spectrum properties defined in NCERT Physics, Infrared rays are produced by hot bodies and molecules. Due to this characteristic, they are commonly known as heat waves. They are primarily responsible for the greenhouse effect, which traps thermal energy.

Step 2 (Deductive Reasoning): [0.25 Mark]

• (A) Gamma rays: High-frequency radiation used in cancer therapy.
• (B) X-rays: Used for diagnostic imaging in medicine.
• (C) UV rays: High-energy radiation causing chemical reactions and skin tanning.
• (D) Infrared rays: Possess frequencies in the range of $10^{11} \text{ Hz}$ to $4 \times 10^{14} \text{ Hz}$, which excite the vibrational motion of atoms and molecules, resulting in the heating effect.

Step 3 (Final Concluded Answer): [0.25 Mark]

The correct option is (D) Infrared rays.

💡 EL10 Concept Insight: Think of infrared rays like the invisible "warmth" you feel when you stand near a campfire or a heater; even though you can't see the rays, your skin senses them as heat because they make the molecules in your body wiggle faster!