Question

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

Answer 1

They slow down so the answer is B

Answer 2

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