Answer
(a) $3.3\times 10^{16}$ Hz (b) Ultraviolet.
Work Step by Step
(a) Velocity, wavelength, and frequency are related using the formula $$v=f\lambda$$ Solving for frequency yields $$f=\frac{v}{\lambda}$$ Substituting known values of $v=c=3.00\times 10^8m/s$ and $\lambda=9.0microns=9.0\times 10^{-9}m$ yields a frequency of $$f=\frac{3.00\times 10^8m/s}{9.0\times 10^{-9}m}=3.3\times 10^{16}Hz$$ (b) According to the range of values provided for the frequency of ultraviolet light on page 884, the light is in the range of ultraviolet light and must be ultraviolet.
