Question

What is the time traveled by a pulse over a distance of lcm in air (n=1) and in 1cm of glass (n 1.5)? What is the difference in picoseconds?

Answer 1

Answer: in air 33.33 ps and in the glass 50 ps: so the difference 16.67 ps

Explanation: In order to calculate the time for a pulse travellin in air  and in a glass we have to consider the expresion of the speed given by:

v= d/t  v the speed in a medium is given by c/n where c and n are the speed of light and refractive index respectively.

so the time is:

t=d/v=d*n/c

in air

t=0.01 m*1/3*10^8 m/s= 33.33 ps

while for the glass

t=0.01 m*1.5* 3* 10^8 m/s= 50 ps

Finally the difference is (50-33.33)ps = 16.67 ps