What determines the wave length.
The Lengths of the different waves and the frequencies are different such as gamma and microwaves being different.i understand how they are different but why
To my knowledge, what determines a wavelength is the frequency (the number of occurances of waves at a given point of time) of a wave. The wavelength is the distance between the troughs and peaks of a wave.
I'd also like to note that the electromagnetic spectrum is made up of both visible, and invisble light, (Radio Waves, to visible light, to gamma rays), so we don't know which type of wave you are speaking of specificly.
"The eternal mystery of the world is its comprehensibility." -Albert Einstein
All matter radiates electromagnetic energy. Each substance has allowable energy levels/wavelengths/frequencies at which it can radiate, and specific temperatures at which it can radiate them (its emission spectrum).
From here on, it gets complicated.