## Chemistry: The Central Science (13th Edition)

A radiation is only visible to human eye if it is in the wavelength range of the visible light, which is from $400nm$ to $750nm$. *Part a): The wavelength of radiation is $10\mu m$, therefore $\lambda = 10\mu m=10000nm$. Since a radiation with a wavelength of $10000nm$ is not in the wavelength range of the visible light, it is not visible to human eye. *Part b): The wavelength of radiation is $545nm$. Therefore, it is in the wavelength range of visible light, which means it is visible to the human eye.