The speed of light is: [tex] c=2.998 \cdot 10^8 m/s [/tex]
The distance that should be covered by the light is: [tex] S=40 cm=0.4 m [/tex]
Therefore, we can calculate the time the light takes to cover this distance by using the basic relationship between space, time and distance:
[tex] t=\frac{S}{c}=\frac{0.4 m}{2.998\cdot 10^8 m/s}=1.334\cdot 10^{-9} s [/tex]
which corresponds to 1.334 nanoseconds.
