Which of the following best describes the relationship between the speed of light and the type of medium?
Light travels faster in solids because of the large distance between solid particles
Light travels slower in solids because of the small distance between solid
particles
Light travels faster in air because of the small distance between air particles
Light travels slower in air because of the large distance between air particles

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.