In air, the speed of light is $3.0 \times 10^8\,\text{m s}^{-1}$. A transparent plastic material placed in air has a critical angle of $37^\circ$. What is the speed of light in the plastic material?
- A$1.8 \times 10^8\,\text{m s}^{-1}$
- B$2.4 \times 10^8\,\text{m s}^{-1}$
- C$3.8 \times 10^8\,\text{m s}^{-1}$
- D$5.0 \times 10^8\,\text{m s}^{-1}$