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Light and Optics

Investigation 1 – Lab

Back to Investigation 1

BE PREPARED

Supplies and Equipment:

Class Materials:

1 swing arm lamp
1 stopwatch
green food coloring
1 sheet of two-toned black-and-white paper
1000 ml water

Group Materials:

3 100 ml beakers
1 glass stir rod
1 100 ml graduated cylinder
1 400 ml beaker
1 funnel
1 dropper pipette
1 flashlight
1 marker
1 sheet of white paper
1 metric ruler
3 2 cm pieces of masking tape
10 paper towels

Individual Materials:

1 Student Data Record

Teacher Preparation:

1. Attach the swing arm lamp to the teacher’s demonstration desk.

2. Place all materials at a central location.

3. Divide students into five cooperative groups.

Instruction:

1. Ask one student from each group to obtain: ten (10) paper towels, one (1) 400 ml beaker with 200 ml of water, three (3) 100 ml beakers, one (1) glass stir rod, one (1) 100 ml graduated cylinder, one (1) funnel, one (1) dropper pipette, three (3) 2 cm pieces of masking tape, one (1) flashlight, one (1) metric ruler, one (1) sheet of white paper, and one (1) marker.

2. Instruct each student group to prepare for the Lab by completing the steps in Problem 2 in their Student Data Record.

GET FOCUSED

Investigation One introduces students to the transmission and absorption of light.

Students will predict which of the three solutions will absorb and transmit the most light.

INVESTIGATE

1. Direct each student group to obtain the following necessary materials from the distribution point: 2 wood blocks, 2 metric rulers, 1 flower pot, 1 triple beam balance, 1 weigh dish, 1 steel marble, 1 plastic marble, 1 marker, and 1 calculator.

Trial 1

1. This Trial is designed to introduce students to the concepts of transmission and absorption of light. Students will dissolve different amounts of food coloring to produce three colored solutions that differ in shade. Students will predict which of the three solutions will absorb and transmit the most light. Students will then test their predictions by using a flashlight to shine light through the three solutions onto a piece of paper placed on the opposite side of the solution from the flashlight. The light intensity reaching the paper will indicate to students the extent of the absorption and transmission of the light.

Does a darker shade of transparent solution absorb more light than a lighter shade?

Does a darker shade of transparent solution transmit more light than a lighter shade?

2. When finished, instruct students to carefully move the three beakers and the flashlight to one side of the table.

Trial 2

3. This Trial is designed as an extension of the previous Trial. In Trial 1, students explored the transmission and absorption of light by transparent solutions of food coloring. This Trial asks students to predict and investigate whether the light or dark-colored side of a sheet of paper absorbs more or less light. Students will investigate the amount of absorption by placing the sheet of paper under the light from a swing arm lamp. Students will judge the amount of absorption by the sheet of paper by feeling both sides of the paper and estimating the temperature of each side.

Will a dark-colored solid object absorb more light than a light-colored solid object?

NOTE: Trial 2 begins with problem 10 in the Student Data Record. It should be started before students complete Problems 6-9 from Trial 1 since Trial 2 requires at least 10 minutes to warm the sheet of paper. While the sheet of paper warms, students should return to Trial 1 and complete Problems 6-9.

a. Ask a student volunteer to place the two-toned sheet of paper under the shade of the lamp at the teacher demonstration desk.

b. Instruct a second volunteer to hold the ruler next to the shade with the zero mark touching the tabletop.

c. Instruct a third volunteer to lower the shade until it is 10 cm above the sheet of paper. Ask the second volunteer to remove the ruler. Instruct a fourth volunteer to start the stopwatch.

d. While the paper is under the lamp, ask students to clean up the lab equipment from the first part of the experiment. After they have finished cleaning up, ask students to return to their lab tables.

4. Ask the student volunteer to look at the time elapsed which should be at least 10 minutes Ask the student volunteers to listen to all of the following directions before performing them:

a. Ask one student volunteer to quickly and carefully remove the sheet of paper from under the lamp.

b. Instruct a second volunteer to quickly and simultaneously touch the black side with one hand and the white side with the other hand. The volunteer should report to the class which side feels warmer.

c. Ask students to record the observations and answer Problem 6 in their Student Data Record.

5. For closure, review the experiment as a class. Ask students the following questions:

- Did the shade of Solutions A, B, and C affect whether the liquids transmitted or absorbed light? Explain. Yes. When the flashlight was shined into Solutions A and B, the light was transmitted onto the paper because the shade of the solutions was light enough for light to be transmitted. Solutions A and B were transparent enough to transmit some light. No light was transmitted through Solution C because the shade of the solution was dark enough to completely absorb the light. Solution C was an opaque liquid.
- Did Solution B both absorb and transmit light? How do you know? Solution B was a darker shade of green than Solution A, yet lighter than Solution C. Because Solution B’s shade of green was between those of Solution A and Solution C, we know that Solution B transmitted less and absorbed more light than Solution A, and transmitted more and absorbed less than Solution C.
- How did your prediction of how each solution would transmit and absorb light compare to your results? Did they agree or disagree? Student answers will vary. Depending on students’ prior knowledge, some students’ predictions may have predicted that lighter shades of color transmit more light than darker shades and that darker shades of color absorb more light than lighter shades. Other students may have predicted that darker shades transmit more light and that lighter shades absorb more light. The results of the experiment should agree with the prediction.

6. On completion of the Investigation allow sufficient time to return all materials to the correct location in the Lab for storage.