A thunderstorm! You see a flash of lightning across the sky. Five seconds later, your hear the thunder. If lightning and thunder come from the same source, then why don't they occur at the same time?
They do! The time difference is due to the way sound waves and light waves travel. Light travels extremely fast through the air, 300,000,000 m/s. Sound travels much slower, 343 m/s through air. Therefore we can see light in an instant, but it takes a while to hear thunder. The speed of light waves and sound waves depends on the medium through which they travel. Take a look at the data in the image above.

How do the speeds of sound and light waves compare?

a. Light waves cannot travel through a dense material like a solid.
b. Sound waves travel fastest through a dense medium like the solid ground.
c. Light waves can travel through a vacuum; sound waves cannot.
d. The speeds of light and sound are affected in the same way in different mediums.
e. The denser the medium, the faster sound travels.