Electromagnetic spectrum regions defined by frequency ranges

Steps:

• Convert 30 THz to Hz: 30 × 10¹² Hz = 3 × 10¹³ Hz.
• Recall microwave range: 3 × 10⁹ to 3 × 10¹¹ Hz (up to 300 GHz).
• Recall infrared range: 3 × 10¹¹ to 4 × 10¹⁴ Hz (0.3 to 400 THz).
• Compare: 3 × 10¹³ Hz falls within infrared (below visible light's 4 × 10¹⁴ to 7.5 × 10¹⁴ Hz).

Why A is correct:

• Infrared radiation spans frequencies from 0.3 to 400 THz, encompassing 30 THz per standard electromagnetic spectrum classifications.

Why the others are wrong:

• B: Microwaves top out at 300 GHz (3 × 10¹¹ Hz), below 30 THz.
• C: Ultraviolet starts above 750 THz (7.5 × 10¹⁴ Hz), higher than 30 THz.
• D: Visible light ranges from 400 to 790 THz, exceeding 30 THz.

Final answer: A