In a perfect vacuum, light waves travel at 300,000 kilometers every second. when light waves travel through materials, such as air, they a. speed up b. slow down c. increase in amplitude d. heat up

c = speed of light in vacuum = 300,000 kilometers/second

n = index of refraction of material

v = speed of light in the material

Speed of light in a given material is given as

v = C/n

v = 300,000/n

for air, the value of index of refraction "n" is slightly greater, hence the speed of light in air is smaller than 300,000 kilometers/second. hence the light waves slow down.

so correct choice is

B.slow down

the gas collects in coils that then becomes a liquid that then flows through the coils inside the refrigerator

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.