An infrared wave traveling through a vacuum has a frequency of 4.0 × 1014 Hz. What is the wave’s wavelength?

In a vacuum, electromagnetic waves travel at about 3.0 × 10⁸ m/s. Wavelength equals speed divided by frequency: (3.0 × 10⁸)/(4.0 × 10¹⁴) = 7.5 × 10⁻⁷ m. So the wavelength is 7.5 × 10⁻⁷ m, choice B.

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