Answer:
the lowest frequency is [tex]7.5\times 10^{14} Hz[/tex]
Explanation:
In the question it is given that wavelength(L) in the range of 200μm to 400μm.
let ν be frequency of wave v velocity = 3\times 10^8
velocity v= Lν
therefore ν=[tex]\frac{v}{L}[/tex]
frequency ν be lopwest when L will be heighest
ν(lowest)=[tex]\frac{3\times 10^8}{400\times 10^-9}[/tex]
ν=[tex]7.5\times 10^{14} Hz[/tex]
