To find the frequency (f) of visible light in terahertz (THz), we can use the relationship between frequency, wavelength, and the speed of light. The speed of light (c) is approximately 3 x 10^8 meters per second (m/s). The wavelength (λ) of visible light ranges from 400 nm to 700 nm. Using the formula f = c/λ, we can determine the frequency of visible light. Since 1 THz equals 10^12 Hz, the frequency of visible light ranges from 4.3 x 10^14 Hz (for 700 nm) to 7.5 x 10^14 Hz (for 400 nm).