I think it is radio waves!
The energy of EM radiation depends on its frequency, and the lowest frequency corresponds to the lowest energy. Radio waves are at the low end of the energy and frequency spectrum.
They are inversely related
The speed at which a wave propagates is the product of its wavelength and its frequency. The wavelength and the frequency vary inversely because the speed of a certain type of wave in a certain type of medium under certain conditions is constant.
Electromagnetic radiation
Hard to believe, but back in the old days, we had red, orange, yellow, green, blue, indigo, and violet. Now, they shorten the list. Who knows what indigo is anyway? Red is the longest wavelength, violet is the shortest. BTW, some people call violet purple, but that's another story.
The longest wavelength / lowest frequency visible light is the red end of the spectrum. The shortest wavelength / highest frequency visible light is the violet end of the spectrum.
The energy of EM radiation depends on its frequency, and the lowest frequency corresponds to the lowest energy. Radio waves are at the low end of the energy and frequency spectrum.
One convenient working definition of 'radio' is: Electromagnetic radiation withfrequency up to 300 GHz / wavelength down to 1 millimeter.'Radio' is our name for the lowest frequency / longest wavelength, so there'sno lower limit on frequency, or upper limit on wavelength.
They are inversely related
Extremely low frequency (ELF) waves have wavelength of the order of 100 megametres ( = 100,000 kilometres).
A photon is a fundamental or elementary particle and the carrier of the electromagnetic field. In this light (no pun intended) it can be applied to all electromagnetic energy, including radio waves. There wouldn't be a "lowest frequency" of electromagnetic radiation that was not photonic. ---- ...or if there was it would have a wavelength the size of the Universe : ) Couldn't carry a whole lot of data there...
The speed at which a wave propagates is the product of its wavelength and its frequency. The wavelength and the frequency vary inversely because the speed of a certain type of wave in a certain type of medium under certain conditions is constant.
In the electromagnetic spectrum, it is the radio wave that has the longest wavelength. Some radio waves are over 100 yards long.
Electromagnetic radiation
Hard to believe, but back in the old days, we had red, orange, yellow, green, blue, indigo, and violet. Now, they shorten the list. Who knows what indigo is anyway? Red is the longest wavelength, violet is the shortest. BTW, some people call violet purple, but that's another story.
the product of wavelength and frequency is speed of propagation for a vacuum about 300,000 km/s, about the same in air, less for glass or water
Immediately adjacent to the band of visible light, on the end with highest frequency / shortest wavelength.