That depends a lot on the order of magnitude of the electromagnetic radiation in question. If it's radio waves or microwaves, you can use a coil of wire hooked up to an oscilloscope (preferably a digital one), and use a function on the device to measure the wavelength.
If it's something between infrared and ultraviolet, including visible light, you'd have to use a special light sensor, though I'm not sure of the name. However, there is a relatively simple experiment that can give you a rough estimate of the wavelength of light you can see:
As for things like X-rays and Gamma rays, sorry, but I have no clue, though I can speculate that it would be possible to take a diffraction based approach such as the one outlined on the link above, but the equipment would surely be more complicated. Not to mention that such forms of radiation are very dangerous.
all of them
Increasing the frequency of any electromagnetic wave ... or of any wave for that matter ... decreases its wavelength.
A gamma ray is an electromagnetic wave. It has the highest frequency (and energy) as well as the shortest wavelength on any wave on the electromagnetic spectrum.
The distance between consecutive crests of a wave. This serves as a unit of measure of electromagnetic radiation.
The wavelength of a signal is calculated by c/f. C is the velocity of the wave and f the frequency of the signal. Wavelength is defined as the distance between any two successive crests or troughs in case of a mechanical wave. In case of longitudinal wave, the distance between two successive compressions or rarefactions will be the wavelength. In case of electromagnetic wave c/f will be the wavelength
There is no maximum wavelength.
By frequency on the electromagnetic spectrum
frequency x wavelength = speed of the wave. This applies to all waves, not just to electromagnetic waves.
Wavelength = 1/Frequency
The higher the frequency, the lower the wavelength. Wavelength
all of them
frequency
The wavelength, E = hc/wavelength.
radio wave is form of electromagnetic energy which has the longest wavelength in electromagnetic spectrum
A gamma ray is an electromagnetic wave. It has the highest frequency (and energy) as well as the shortest wavelength on any wave on the electromagnetic spectrum.
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... shorter in wavelength.