Electromagnetic Spectrum Wavelength Ranges

Steps:

• Recall standard wavelength ranges: visible light (400–700 nm), infrared (700 nm–1 mm), microwaves (1 mm–1 m), radio waves (>1 m).
• Convert 2.1 cm to meters: 2.1 cm = 0.021 m.
• Compare 0.021 m to ranges: it falls between 1 mm (0.001 m) and 1 m.
• Match to microwave region.

Why B is correct:

• Microwaves span wavelengths from 1 mm to 1 m, and 2.1 cm (0.021 m) fits directly within this defined range.

Why the others are wrong:

• A: Infrared wavelengths are shorter, up to 1 mm (0.001 m), so 2.1 cm exceeds this.
• C: Radio waves have wavelengths longer than 1 m, so 2.1 cm is too short.
• D: Visible light wavelengths are 400–700 nm (0.0004–0.0007 m), far shorter than 2.1 cm.

Final answer: B