In empty space, the primary difference between visible light and radio waves lies in their wavelengths and frequencies, while their speeds remain the same.
Wavelength: Visible light consists of a range of wavelengths within the electromagnetic spectrum, typically ranging from approximately 400 to 700 nanometers (nm). These wavelengths correspond to different colors, with shorter wavelengths appearing as violet and longer wavelengths appearing as red. On the other hand, radio waves have much longer wavelengths, typically ranging from a few millimeters to kilometers or even longer.
Frequency: Frequency is the number of complete cycles of the wave that occur per unit of time. It is inversely related to wavelength, so as wavelength increases, frequency decreases. Visible light has higher frequencies compared to radio waves. The frequency range for visible light is typically around 430 THz (terahertz) to 750 THz, corresponding to the various colors within the visible spectrum. In contrast, radio waves have much lower frequencies, typically ranging from a few kilohertz (kHz) to several gigahertz (GHz) or even higher.
Speed: In empty space, both visible light and radio waves travel at the same constant speed, known as the speed of light. This speed, denoted by the symbol 'c', is approximately 299,792,458 meters per second (m/s) in a vacuum. Therefore, both visible light and radio waves travel at this speed when propagating through empty space.
To summarize, the key difference between visible light and radio waves in empty space lies in their wavelengths and frequencies. Visible light has shorter wavelengths and higher frequencies, corresponding to the colors we perceive, while radio waves have much longer wavelengths and lower frequencies. However, both types of waves travel at the same speed, the speed of light, in a vacuum.