Speed and frequency are two distinct properties of an electromagnetic wave:
Speed: The speed of an electromagnetic wave refers to the rate at which the wave propagates through a medium or through space. In a vacuum, electromagnetic waves, including light, travel at a constant speed, denoted as the speed of light (c), which is approximately 299,792,458 meters per second (or about 186,282 miles per second). In other media, such as air, water, or glass, electromagnetic waves typically travel at slightly slower speeds due to interactions with the medium.
Frequency: The frequency of an electromagnetic wave refers to the number of complete oscillations or cycles the wave completes per unit of time. It represents the rate at which the wave's electric and magnetic fields oscillate. Frequency is typically measured in hertz (Hz), where one hertz corresponds to one cycle per second. Electromagnetic waves can have a wide range of frequencies, spanning from extremely low frequencies (ELF) in the range of a few hertz to extremely high frequencies (EHF) in the terahertz (THz) or even petahertz (PHz) range.
The relationship between speed and frequency of an electromagnetic wave is determined by the equation:
c = λf
where:
- c is the speed of light,
- λ (lambda) is the wavelength of the wave, and
- f is the frequency of the wave.
This equation states that the speed of light is equal to the product of the wavelength and the frequency of the wave. Therefore, if the frequency of an electromagnetic wave increases, its wavelength decreases, and vice versa, while the speed remains constant.
In summary, speed refers to the rate of propagation of an electromagnetic wave, while frequency represents the number of cycles or oscillations the wave completes per unit of time. The speed of light is constant in a vacuum, while the frequency of the wave determines its energy and the type of electromagnetic radiation (e.g., radio waves, visible light, X-rays) it corresponds to.