• Tags: spectrum, applications, comparison
• Difficulty: Foundation

Key comparative facts for JEE: (1) All EM waves have the same speed in vacuum (c), but different frequencies produce vastly different interactions with matter. (2) Energy E = hf: gamma rays are most energetic, radio waves least. (3) Penetrating power increases with frequency (gamma > X-ray > UV > visible > IR > microwave > radio). (4) Ionizing ability also increases with frequency — UV and above can ionize atoms. (5) The atmosphere is transparent to visible light and radio waves, but absorbs most UV (ozone), IR (water vapor, CO2), and X-rays/gamma rays. The "optical window" and "radio window" allow astronomical observation. (6) All EM waves can be polarized (transverse nature). (7) The boundaries between regions are not sharp — they overlap. The classification is based on how the radiation is produced and detected, not on any fundamental physical difference.