Waves: Light and Sound — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. In Grade 4 science, light always travels faster than sound in air.
Light speed is far greater than sound speed in air.
2. Grade 4 fact: sound waves travel faster through water than they do through air.
Tighter molecules pass vibrations along more quickly.
3. We see lightning before we hear thunder because the light reaches our eyes first in Grade 4 lessons.
Light arrives almost instantly; sound takes seconds per kilometer.
4. The material a wave moves through is called the medium in Grade 4 science.
A medium is the matter waves travel through.
5. Sound waves cannot travel through empty space, but light waves can in Grade 4 class.
Sound needs particles; light can move through a vacuum.
6. Sound usually travels faster through solids than through liquids in Grade 4 textbooks.
Solids transmit vibrations fastest because particles are close.
7. Counting seconds between lightning and thunder helps you guess how far the storm is in Grade 4.
Sound takes about 3 seconds to travel one kilometer.
8. The path of energy from a source to your senses can be called a signal in Grade 4 science.
Waves carry signals such as sound or light to a receiver.
9. Sending a wave from one place to another is called transmission in Grade 4 lessons.
Transmission is the movement of a wave or signal between points.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Grade 4: sound speed in air vs water
→ Faster in water
Faster in water
Grade 4: lightning then thunder
→ Light arrives first
Light arrives first
Grade 4: medium
→ Material a wave moves through
Material a wave moves through
Grade 4: vacuum of space
→ Sound cannot travel here
Sound cannot travel here
Wave speed depends on the medium; light is fastest and needs no medium.