Which statement describes the relationship between wavelength and frequency for electromagnetic waves?

• A. Wavelength is inversely related to frequency
• B. Wavelength is directly proportional to frequency
• C. Wavelength is independent of frequency
• D. Wavelength increases with frequency

Answer: (A)

Wavelength and frequency are linked by the wave’s speed. For any electromagnetic wave, the speed equals the product of wavelength and frequency: λ f = v. In vacuum, v is the speed of light, so c = λ f. Since c is a constant, the wavelength must decrease when the frequency increases, and increase when the frequency decreases. In other words, wavelength and frequency are inversely related in a given medium. Doubling the frequency halves the wavelength, and halving the frequency doubles the wavelength. This inverse relationship is the correct description because it stems from the constant propagation speed of light. The other ideas would imply that wavelength grows with frequency, stays the same regardless of frequency, or is independent, which contradicts the fixed speed connection.