Worksheet

Color Filters and a String Phone: A Science Fair Wave Project

Grade 8 waves practice: a science fair project with colored filters and a string phone models how materials reflect, absorb or transmit light and sound.

Grade 8ScienceInteractive · Printable

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Single worksheet
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1 NGSS standard
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11 questions
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Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Sorting, Short answer

About this worksheet

What students practice

Students use filter data to model which colors of light a material transmits or absorbs.
Students use string phone data to explain how a solid line transmits sound and how soft materials absorb it.
Students argue from evidence that materials can absorb wave energy, not only reflect or transmit it.

How to use

If you can, show a piece of colored cellophane and a cup-and-string phone first. Remind students that 100 units of light and a 10 dB rise are explained in the project notes.

Curriculum

NGSS standard covered

MS-PS4-2

Model how light and sound waves are reflected, absorbed or transmitted through different materials.

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Color Filters and a String Phone: A Science Fair Wave Project

Use two students' fair data to model how materials transmit, absorb and reflect light and sound.

Part 1: The filter test

Read the project notes, then use them and Table 1 to answer the questions.

Project Notes: What Happens When a Wave Meets a Material?

1For the district science fair, eighth graders Zainab Thorsen and Marek Oyelaran wanted one project that tested both kinds of waves their class had studied, light and sound. Their question was simple: what happens to a wave when it reaches a material? Their teacher, Mr. Cosimo Ferrante, reminded them that a material can reflect a wave, sending it back; absorb it, taking in its energy, which often warms the material a tiny bit; or transmit it, letting it pass through. Most materials do some of each, so the team decided to measure how much of each wave got through.

2For the light test, they cut a hole in the side of a shoebox and put a light sensor inside, 20 cm from the hole. They used three small LEDs, one red, one green and one blue. Each LED, shining through the open hole, gave a reading of exactly 100 units. Then they taped a filter over the hole: clear plastic, or red, green or blue cellophane, a thin colored plastic film you can see through. They also stacked the red and green filters together. A second sensor next to the LEDs showed that every filter sent about 8 units of each color back toward the LED. They kept the LEDs, the hole and the distance the same and changed only the filter and the color.

3For the sound test, they built a string phone: two paper cups whose bottoms were joined by a line 10 m long. Lab stands held both cups still, so the line could be pulled tight or left to sag. A phone speaker played a steady 500 Hz tone at the same volume into cup A, and a sound meter app on a second phone sat inside cup B. They tried different lines and changes to the line while keeping the cups, the distance, the tone and both phones the same. With the speaker off, the quiet room read 30 dB. Each rise of 10 dB means about 10 times as much sound energy reaching the meter.

4Marek also tried two changes to the tight nylon line. First he pinched the middle of the line between his finger and thumb. Then he wrapped a strip of soft felt around the middle of the line, without pulling on it. The team ran each setup three times and recorded the average reading.

Table 1: Light Reaching the Sensor (100 units with no filter)
Filter over the hole	Red LED	Green LED	Blue LED
None	100	100	100
Clear plastic	92	92	92
Red cellophane	80	6	4
Green cellophane	8	70	12
Blue cellophane	5	14	72
Red and green stacked	6	4	under 1

Use paragraphs 1 and 2 and Table 1. The green LED sends 100 units of light toward the red cellophane.

The red cellophane absorbed about units of the green LED's light.

Use Table 1 and paragraph 2. Sort each filter and LED by what happened to most of the light that reached the filter.

Clear plastic with the blue LEDRed cellophane with the blue LEDRed cellophane with the red LEDGreen cellophane with the red LEDBlue cellophane with the green LEDGreen cellophane with the green LED

Most was transmitted	Most was absorbed

Marek shines a white flashlight, whose light is a mix of colors including red, green and blue, through the green cellophane onto a white card. The spot on the card looks green. Which model fits Table 1 best?

A. The cellophane adds green color to the white light as the light passes through it.
B. The cellophane reflects green light forward onto the card and lets red and blue light pass by.
C. The cellophane transmits most of the green light and absorbs most of the red and blue light.
D. The cellophane bends the red and blue light so that it lands on the inside of the box.

Before the test, Zainab guessed that the red and green filters stacked together would let through about as much light as one filter alone. Which model best explains the stacked results in Table 1?

A. The stacked filters were twice as thick, so they transmitted about half as much as one filter.
B. Light that gets through one filter is mostly a color the other filter absorbs, so little gets through both.
C. The two films stuck together and reflected about 90 units of each color back toward the LEDs.
D. The second filter changed the red light into green light, which the sensor reads more weakly.

Use this model: a filter lets through the same fraction of a color no matter how much of that color reaches it. The green LED shines through the green cellophane, then through the blue cellophane. Use Table 1 and round to the nearest whole number.

About units of the green LED's light would reach the sensor.

Part 2: The string phone test

Use paragraphs 3 and 4 and Table 2. Each reading in Table 2 is the average of 3 runs.

Table 2: Sound Level Inside Cup B (500 Hz tone, cups 10 m apart)
Setup	Sound level (dB)
Speaker off (quiet room)	30
No line, air only	38
Tight cotton string	52
Tight nylon fishing line	58
Sagging nylon fishing line	39
Tight nylon line, pinched in the middle	40
Tight nylon line, felt around the middle	47

Use Table 2. Compare the tight nylon fishing line with no line.

The tight nylon line raised the sound level in cup B by dB.

Use your answer to question 6 and the rule at the end of paragraph 3.

With the tight nylon line, about times as much sound energy reached the meter as with no line.

Circle the two comparisons that are evidence that the tight line, not the air between the cups, carried most of the sound energy to cup B.

Speaker off 30 dB, no line 38 dBTight nylon line 58 dB, no line 38 dB, cups 10 m apart both timesThe tone was 500 Hz in every runTight nylon line 58 dB, the same line pinched in the middle 40 dB

Wrapping felt around the middle of the tight nylon line lowered the reading from 58 dB to 47 dB. Which model explains this result best?

A. The felt made the line vibrate at a higher frequency, which the meter in cup B read as a lower level.
B. The felt reflected the vibrations forward toward cup B, which made the tone in cup B louder than before.
C. The thicker felt transmitted vibrations better than the thin line, so the tone in cup B was stronger.
D. The soft felt absorbed part of the vibration energy, so less was transmitted along the line to cup B.

10.

The sagging nylon line gave 39 dB, while the same line pulled tight gave 58 dB. Which conclusion fits Table 2 best?

A. A sagging line transmits little of the vibration, so cup B gets about what the air alone carries.
B. The sagging line carried more energy than the tight line, but it took longer to arrive.
C. Nylon is a poor material for string phones, so the team should switch to cotton string.
D. The sagging line reflected the 500 Hz tone back to cup A and doubled the level there.

11.

Zainab says, "When a wave reaches a material, it either goes through or bounces back. Nothing else can happen to it." Do you agree? Write a claim, give evidence from Table 1 and Table 2, and explain your reasoning using the words reflect, absorb and transmit.