Waves: Light and Sound — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A Grade 4 student shines a flashlight at a flat mirror. What happens to most of the light?
A) It is absorbed and turns into heat inside the mirror.
B) It is reflected back at an equal angle.
C) It is refracted and bends straight downward.
D) It disappears completely with no path.
In Grade 4 science, smooth shiny surfaces like mirrors reflect light. The light bounces off at the same angle it came in, which is why we can see clear images.
2. Why does a black T-shirt feel hotter in the sun than a white T-shirt?
A) Black shirts reflect more light than white shirts.
B) Black shirts absorb more light energy and turn it into heat.
C) Black shirts refract sunlight into rainbows.
D) Black shirts let light pass through without changing.
Grade 4 learners connect color to absorption. Dark surfaces absorb most wavelengths of light, and that energy becomes heat. Light surfaces reflect more, so they stay cooler.
3. A pencil placed in a glass of water looks bent at the water line. What is happening?
A) The pencil really breaks when it touches water.
B) Light is absorbed by the pencil completely.
C) Light refracts (bends) as it passes between water and air.
D) Sound waves push the pencil sideways.
In Grade 4 science, refraction is the bending of light when it changes speed between materials like water and air. The pencil only looks bent because of this bending.
4. Which Grade 4 example best shows light being mostly absorbed?
A) Sunlight bouncing off a clean mirror.
B) A beam of light bending through a magnifying glass.
C) Sunlight hitting dark asphalt and warming it up.
D) A flashlight shining through clear glass.
Grade 4 students recognize absorption when light energy is taken in by a surface and turned into heat, like dark asphalt warming up in the sun.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When light bounces off a smooth surface and changes direction, that is called reflection.
Grade 4 learners use 'reflection' for any time light bounces. Smooth surfaces reflect cleanly; rough surfaces scatter the reflected light.
2. When a dark surface takes in light energy and warms up, that is called absorption.
In Grade 4 science, absorption removes light from the wave and stores its energy in the material as heat or other forms.
3. When light bends as it passes from air into water or through a lens, that is called refraction.
Grade 4 students learn that refraction happens because light travels at different speeds in different materials, so it bends at the boundary.
4. Sound can also reflect off a hard wall or cliff, and the reflected sound we hear is called an echo.
In Grade 4 science, an echo is sound reflection. The wave bounces back to the listener after a small delay because sound takes time to travel.
5. Soft pillows and thick curtains help quiet a room because they absorb sound waves.
Grade 4 learners connect absorption of sound to insulation. Soft, fluffy materials catch sound waves and turn their energy into a tiny bit of heat, so we hear less echo.