Look for: All three materials reflect light and two tra…

3.B Use evidence to modify a model to explain how an object’s material (structure) influences the path of light as it transmits through or reflects off the material (function).

As students discuss their observations in small groups and as a class, listen for the following:

• All three materials reflect light and two transmit light.
• The one-way mirror reflects more light than the glass but less than the regular mirror; the one-way mirror transmits more light than the regular mirror but less than the glass.
• Using a tool to measure the amount of light transmitted through and reflected off each material would give us data that would make our comparisons more accurate and help us better represent what we observe in a consensus model.

As students revise the class consensus model, the following ideas should be represented for each material:

• Light travels in straight lines.
• When light shines on an object, it can pass through, bounce off, or do a combination of both.
• Arrows should show the direction light travels (path of light, POL) from the source and then when it bounces off or goes through a material.

The Light Interactions Investigation is the students’ first opportunity to observe and compare how light interacts with the one-way mirror, glass, and a regular mirror. The small-group and class discussions give them opportunities to try to make sense of the one-way mirror phenomenon using qualitative data. If they struggle to make comparisons, guide them as follows:

• Focus on students’ observations of the amount of light transmitted through each material, one at a time, and document them on chart paper.
• Move to observations of the amount of light reflected off each material, one at a time, and document them on chart paper.
• Compare the amount of light transmitted by the one-way mirror with the other two materials. This should help students see that the one-way mirror’s data falls somewhere between the other two.
• Then compare the amount of light reflected by the one-way mirror with the other two materials. Again, students should be able to determine that the one-way mirror falls somewhere between the other two.
• After making these comparisons, students should notice that they can only compare the three materials using words like “more” and “less” but cannot be much more accurate than this.

While revising the consensus model, if students struggle to represent what they observed, guide them to build the model using a systematic process such as this:

• Focus on one material at a time.
• Draw the material in a zoomed-in bubble.
• Represent light (using a straight arrow) coming into contact with the material.
• Represent what light does after it hits the material using arrows, as appropriate.
• Repeat the process with each material.

Summarize observations and determine next steps. Show slide G. Say, We know light bounces off all three materials, because we saw the light shine on each material and reflect back at us. We also know light goes through glass and the one-way mirror, because we saw the light shine on each material, then go through and shine on the wall behind it. What we don’t know is how much light transmitted through or reflected off each material. How might measuring the amount of light that transmits and reflects be important for explaining the one-way mirror phenomenon? How could we determine how much light transmits and reflects?

Give students a minute to turn and talk with a partner, before discussing a few students’ ideas as a class.

Suggested prompt

Sample student response

How might measuring the amount of light that goes through and bounces off the one-way mirror be important for explaining the one-way mirror phenomenon?

• We do know the amount of light in a room affects how the one-way mirror behaves. In a lit room, it acts like a mirror, and in a dark room, it acts like a window.
• If we know the amount of light that goes through and bounces off the one-way mirror, the glass, and the regular mirror, we can make even better comparisons between the three materials, which might help us figure out what is happening when the light hits the one-way mirror.

How could we determine how much light goes through and how much bounces off?

• The amount of light seems to be an important part in the system. If we want to understand why the one-way mirror acts differently in different amounts of light, we need a way to measure how much light is going through and how much is bouncing off each material.
• Say, Since we think it is probably a good idea to determine how much light goes through and bounces off each material, we need to figure out how we can investigate that.