A light wave moves through a glass block at a speed of $2.0 \times 10^8\,\text{m s}^{-1}$. Within the glass, its wavelength is $4.0 \times 10^{-7}\,\text{m}$. What is the frequency of the light?
- A$2.0 \times 10^{-15}\,\text{Hz}$
- B$1.3 \times 10^{-2}\,\text{Hz}$
- C$80\,\text{Hz}$
- D$5.0 \times 10^{14}\,\text{Hz}$