In high-frequency diathermy, a wavelength of 22 meters corresponds to which frequency?

• A. 27.12 MHz
• B. 40 MHz
• C. 13.56 MHz
• D. None of the above

Answer: (C)

The key idea is how wavelength and frequency relate for electromagnetic waves: f = c/λ, where c is about 3×10^8 m/s in free space. If the wavelength is 22 meters, the frequency is 3×10^8 divided by 22, which is roughly 13.6 MHz. In HF diathermy, 13.56 MHz is a standard medical frequency, so it aligns with both the calculation and typical usage. Checking the other options, they would correspond to shorter wavelengths (about 11 m for 27.12 MHz and about 7.5 m for 40 MHz), not 22 m. Therefore, 13.56 MHz is the best match.