Waves: Light and Sound — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
We can see objects in a totally dark room with no light at all.
Corrected: We need light to bounce off objects so our eyes can see them.
In Grade 4 science, vision works because light from a source hits an object, reflects, and enters our eyes. Without light, no reflection happens and we see nothing.
2. Fix the sentence:
The moon makes its own light just like the sun does.
Corrected: The moon reflects light from the sun; the sun is the real light source.
Grade 4 students learn the difference between light sources (sun, lamp, fire, flashlight) and reflectors. The moon is bright because sunlight bounces off it.
3. Fix the sentence:
An opaque object lets all the light pass through it clearly.
Corrected: An opaque object blocks light from passing through.
In Grade 4 science, opaque means light cannot pass through, transparent means light passes through clearly, and translucent means some light passes but the image is blurry.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. The sun, a lamp, and a candle flame are all examples of a light source.
Grade 4 learners identify light sources as objects that produce their own light. Without a source, there are no light waves to start with.
2. We see a red apple because light bounces off the apple and into our eyes.
In Grade 4 science, vision is reflection plus detection. Light hits the apple, reflects, and our eyes catch those waves so we see the color.
3. A clear glass window is transparent, which means light passes straight through it.
Grade 4 students sort materials by how light passes through them. Transparent materials like clear glass let almost all light through with a sharp image.
4. Frosted bathroom glass is translucent because some light passes through but the image is blurry.
In Grade 4 science, translucent materials scatter light. You can tell it is bright on the other side, but you cannot see clear shapes.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. How does light from the sun help a Grade 4 student see a soccer ball on the playground?
Sample answer: Light waves travel from the sun, which is a source, all the way to the soccer ball. The ball reflects some of the light back into the air. Those reflected light waves enter the Grade 4 student's eyes, and the brain understands the shape and color of the ball.
Grade 4 standard 4-PS4-2 expects students to describe seeing as light entering the eye after reflecting off an object.
2. Compare an opaque book and a transparent plastic bag for letting light through.
Sample answer: An opaque book blocks light, so a Grade 4 student cannot see through it and a shadow forms behind it. A transparent plastic bag lets almost all the light pass through, so the student can see the shape and color of items inside the bag.
This Grade 4 answer compares two ends of the light-transmission scale, which helps build the idea that materials interact differently with light.