# Refracting Telescopes: Day 1

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## Objective

Students will be able to engage in scientific discourse with text and use characteristic properties of waves (refraction) to design a solution to a problem.

#### Big Idea

Students use text to engage in scientific discourse and then use their knowledge of refraction to design a telescope!

## Introduction and Connections to the NGSS and the Common Core

This lesson is designed to provide students the opportunity investigate and learn about some different ways that waves can be used in the real world while connecting to mathematical and computational thinking to evaluate wave properties.  Specifically, this lesson connects to the following NGSS and Common Core Standards:

MS-PS4-1  Use mathematical representation to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.

MS-PS-4-2  Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

Disciplinary Core Idea PS4.B states that one idea important for students is that the path that light travels can be traced as straight line, except at surfaces between different transparent materials.  In order to demonstrate this, students will experiment with various thicknesses of convex lenses to calculate focal points of telescope lenses.  This again allows students to utilize mathematical and computational thinking to evaluate the properties of waves (SP5).

Moreover, this lesson has a text strategy component that aids students in reading for scientific discourse and citing evidence from text as they recognize the different ways that one can interact with a scientific text (SP7 and SP8).

## Connecting to the Essential Question: What am I going to be learning today?

5 minutes

Ask students, “What are you supposed to learn today?”.  Students should respond by stating something connected to the NGSS Essential Question (I keep this posted on my front board.).  Thus, students might say, “We need to answer the question, what are the characteristic properties of waves and how can they be used in the world?”

In the past lessons, the students have been exploring the following concepts and connecting these ideas to the electromagnetic spectrum:

1. Every wave has a specific wavelength and frequency.
2. Because light can travel through space, it cannot be a matter wave (mechanical) like sound or water waves.
3. There is an inverse relationship between frequency and wavelength.
4. Waves are used in the world to meet our societal needs and wants.

Ask the students to take a moment and add anything new to the light bulb they have been filling out over the past days that seems pertinent.  Then, as a class, allow students to share the new ideas they added and encourage other students to add to their light bulb if a student shares something that they do not already have.

## Mini Lesson: Interacting with Scientific Text and Scientific Discourse

20 minutes

On a document camera (or whatever projecting device you have available), model this for the students by interacting with a science text.  Below is a video demonstrating how I might model this.  I chose to use a text about telescopes as that will be a topic of the lesson.  While modeling, make your thinking visible.  Talk about all of the thoughts that go through your head as a reader.  Students benefit greatly from being let inside the head of a successful reader so that they can see what successful readers do behind the scenes.   With each interaction, be sure to connect it to a “rung” on the ladder.

Provide the students with a copy of the article excerpt, “How Telescopes Work”.  Tell the students that they are reading for the following three specific purposes:

1. Characteristic properties of waves.
2. Ways that waves are used in the world.
3. Evidence that technologies have limitations and are driven by our societal needs and wants.

Ask them to write on sticky notes as they make connections while they read. The picture below on the right is showing a strategy that many of my visual learners like to do. They mark up their text in a color coded fashion with each color representing a "rung" on the "Ladder of Discourse.

After students have read and created sticky notes, place chart paper on each table or group area.  Ask the students to draw a ladder with four rungs on it labeled “Tweets”, “Huh?”, “Found it!”, and “Discourse”.  Ask each member of their group to place each of their sticky notes on the rung that it demonstrates.   Then as a class, ask each group to share one sticky note per rung for the class.  First, ask each group to share one “Tweet”.  Then, ask each group to share one, “Huh?”, “Found it!” and “Discourse”.

One core idea in the NGSS Framework focuses on the influences of engineering, technology and science on society and the natural world. Specifically in middle school, students should recognize the uses and limitations of technologies as well as recognize that new technologies are driven by our societal needs, desires, and values.

Say, “Engineers develop new technologies that are driven by our societal needs and wants. However, each of these technologies have limitations and benefits.  What evidence can you cite from the text that demonstrates this?”  When students respond, they should include the paragraph and line of the text that they find their information in so that the class can follow along. For example, a student might say, “In the second paragraph under ‘Other telescopes’, it mentions that x rays are partly blocked by the earth’s atmosphere so they need to be at high altitudes to work. This shows a limitation of an x-ray telescope.

## Designing Refracting Telescopes

40 minutes

Materials*:

Metersticks

Notecards

3 thicknesses of convex lenses

Meterstick Stands (bottom left of picture)

Notecard Holder for Meter Sticks (see the center of the picture, item with triangular shaped bottom)

Lens Holder for Meter Sticks (just to the left of the notecard)

Provide each student with a Telescope Lab Sheet.  Go through the “Background Knowledge” section with the students, reviewing what “refracting” means.  Explain that one important idea is that the path that light travels can be traced as a straight line, except at surfaces between different transparent materials.  In order to demonstrate this, students will experiment with various thicknesses/curvatures of convex lenses to see how the light refracts with each.

Introduce to the students the idea of a focal length.  Explain that when light bends through a lens, the light meets (converges) at one point, called the focal point.  Hold up a meter stick with a lens and note card attached and show how moving the note card closer and farther away can focus an image on the notecard.  Show the students that they can use the graduations on the meter stick to measure in centimeters the distance from the lens to the note card when it is at its most focused point and that this is the focal length.  The picture below demonstrates the picture in focus on the note card and the triangle points at the bottom of the holders that can be used as end points of measurement on the meter stick. In this case, the focal length of this lens would be about 6 cm.

Explain to the students that there will be two parts to this lab.  First, using the 3 different lenses, calculate the focal lengths.  For this portion of the lab, emphasize to students that they will only need one lens at a time.

For the second part of the lab, I tell the students that I noticed a suspicious sign on the window on the opposite side of the courtyard.  With all of the snow and cold, I really do not want to go outside.  Engineers respond to societal needs and wants and develop technologies that can support those desires.  So, I ask them, as engineers, to develop a refracting telescope that can most effectively help me read what the sign says.  Ask the students to try many different designs collecting both quantitative and qualitative data for each design.  Ask the students, “What quantitative data could you collect?”.  Students should respond, “We could calculate the magnification.”   Ask the students, “What qualitative data could you collect?”.  Students might say, “In general, how easy it is to read the sign or how focused the sign is.

Explain to the students that refracting telescopes have two lenses and that the combination of different lenses can change the magnification of a telescope.  Before designing, encourage them to interact with the text (using the Ladder of Discourse of course!) provided in the "Background Knowledge" section of the student lab document.

Let the students know that they will not finish today and that they will have the next class period to continue developing their telescopes tomorrow.

Note to Teacher:  The "Background Knowledge" section explains that can be found by dividing the focal length of the lens nearest to the eye into the focal length of the lens farthest from the eye.  Or, magnification = focal length of the farthest lens divided by the focal length of the eye piece.  For example, if the focal length of an eye piece was 4 cm and the focal length of the other piece was 8 cm, the telescope would magnify objects 2 times bigger (8 divided by 4 = 2). The picture on the left below shows one possible set up of a refracting telescope and the picture on the right below is a picture looking through a refracting telescope at the window across the courtyard.  Notice the magnification of the window.

In order for students to succeed at creating the most effective telescope, they will need to recognize how changing the lenses can change the magnification and that the effectiveness of the system will change with the change in the proportion of the focal lengths (XC-SPQ-MS-2, XC-SSM-MS-2).

*Some sources for this relatively inexpensive equipment are Science First, and Enasco

## Closure: Exit Ticket

5 minutes

With about 5 minutes left of class, ask each group to fill out an exit slip with the following question:  “Why do you think that the various lenses had different focal lengths?”  As this is the first day in the lab and they are just developing their understanding, each group discusses and then completes one exit slip as a group.  This question is also asked on the lab document so each student will eventually have to answer this question themselves.  I just like to use this exit slip as a gauge to see if students are connecting focal length to the idea that different thickness/curvatures of the lens are causing the light to bend, or refract more than others.  My hope is that they recognize that the thicker/more curved the lens is, the focal length is shorter because the light bends more sharply.  The responses on this exit slip lets me know how much in the next class I need to review refraction and the way that light bends as it passes through transparent material.