SHPE Foundation SHPE Jr. Chapter Curriculum Hands-on Activity Training TeachEngineering Hands-on Activity: * Estimating the Storage Capacity of a CD/DVD TeachEngineering Digital Library: teachengineering.orgteachengineering.org

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General Advice Be prepared! Do each activity beforehand Make sure all materials are available Keep students on task Follow the time frame Be flexible Have Fun!! SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training

Estimating the Storage Capacity of a CD/DVD Behavior of light waves, storage capacity of CDs and DVDs Engineering focus: o Engineering Research/Analysis Students estimate the storage capacity of CDs and DVDs by assessing diffraction patterns of green and red laser beams. Students create a set up for measuring the angle of use equations based on the diffraction of light waves to calculate data. Students analyze results and relate their understanding to the storage capacity of CDs and DVDs. Learning objectives: o Describe how a CD or DVD stores information. o Explain that the laser's wavelength limits how small the pits on a CD or DVD can be. o Explain why a Blu-ray disc can store more information than a CD or DVD. SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Full Activity on TeachEngineering

Suggested time: 30 minutes Suggested group size: 4 students/group Materials o Each group needs: DVD CD (compact disc) red or green laser pointer; red ones cost less than $10 each; green ones cost ~$30 each protractor small spacers to place under protractor (such as cardboard pieces) plain white sheet of paper calculator Estimating Storage Capacity Worksheet, one per student Estimating Storage Capacity Worksheet tape o For the instructor (optional): projector to show students the Estimating Storage Capacity Presentation (optionally the 5 slides could be printed and provided to students as a handout)Estimating Storage Capacity Presentation Estimating Storage Capacity Worksheet Answers SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training /uoh_/activities/uoh_diffraction/uoh_diffraction_activity1.xml Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Engineering Connection (Real World Application): Optical science engineers and materials science engineers design and create devices that satisfy the ever increasing demand for digital storage. The advancement from CDs to DVDs allows more storage per disk but also provides challenges for engineers because the physical structures ("pits") that store data on the disks become smaller and the CD/DVD players' lasers operate at the diffraction limit (resolution) of light. In this activity, we will see how light, its interaction with matter, and the behavior of light waves apply to our everyday lives through engineering and technology! Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Vocabulary TermsDefinitions angle of incidence Angle between an incident light ray and the normal of the surface. constructive interference Phenomenon in which two wavers superimpose to form a resultant wave of greater amplitude. diffraction grating Optical component with a periodic structure that diffracts light into multiple beams. Transmission diffraction gratings are light- transmissive, like lenses; reflective diffraction gratings are light- reflecting, like mirrors. diffraction order Integer corresponding to a diffracted beam. bit Binary digit. Basic unit of information. One bit can be represented by 0/1 or on/off. Eight bites correspond to one byte. byte Unit of digital information. Often used with a prefix, such as MB (megabyte) or GB (gigabyte). One byte consists of eight bits. pit Microscopic indentation on CD/DVD that store on bit. pitch Distance between two neighboring spiral tracks. Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Introduction/Motivation: o (Hold up a CD in one hand, a DVD in the other hand.) Here I have one CD and one DVD. Can you tell which one is which? (Listen to students answers.) What is the difference between a CD and DVD? (Answer: The amount of storage capacity.) o The rate of technological development is quickly increasing. Now we have Blu- rays, which are optical disc storage media just like CDs and DVDs, but can even store more information. However, Blu-ray players require a blue laser. After this activity you will understand why Blu-ray discs only work with blue lasers and not with lasers of higher wavelengths, such as red or green lasers. o How do we measure the size of digital data? Answer: Digital data is measured in bytes, which is usually used with a prefix giga (109) or mega (106)) A byte is a unit of digital information. One byte consists of eight bits. One bit only has two states: 0/1, which can be regarded as on/off. All digital information is stored in the form of bits. You can think off it as huge lines of zeros and ones. Your cell phone, computer, TV, and iPod store your data in the form of long sequences of zeros and ones. Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Introduction/Motivation (cont.): o CDs and DVDs store large amounts of binary data (those patterns of 0s and 1s), which a CD/DVD player can read using a laser, optical devices and sophisticated electronics. o CDs and DVDs are made mostly of plastic (polycarbonate) and can store more information by having multiple recording layers. The data is stored in a series of tiny pits, arranged in a spiral, tracking from the center of the disk to the edge. Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Introduction/Motivation (cont.): o The data layer is coated with a thin layer of aluminum or silver, making it highly reflective. If stretched out, this spiral of pits would be about 5 km long! The pit length and the distance between pits define the digital data. The depth of a pit is 0.11 μm and the width is 0.5 μm. Its length varies between 0.83 and 3.56 μm. o The spiral of pits is a periodic structure that diffracts light into multiple beams. Such a periodic structure is called diffraction grating. The microscopic diffraction grating is the reason why you see beautiful rainbow colors when white light illuminates a CD. o When a laser beam is reflected off the disc, a diffraction pattern is formed. Estimating the Storage Capacity of a CD/DVD D_CD_pits.PNG

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Introduction/Motivation (cont.): o The angle of incidence is the angle of the incoming laser beam with respect to the normal of the CD surface. If the angle of incidence is close to the normal, the condition for constructive interference is identical to that for a transmission diffraction grating, which is given by the following equation: Estimating the Storage Capacity of a CD/DVD o m is the diffraction order, o d is distance between the rows of pits o θ is the angular position of the m th maximum o The red laser has a higher wavelength than the green laser. You will find the wavelength on the laser. (Red is commonly 650nm. Green is 532nm.) Blue lasers have even shorter wavelengths, but are more expensive.

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Introduction/Motivation (cont.): Estimating the Storage Capacity of a CD/DVD o The distance between the rows of pits, d, can be estimated by: d=mλ/sin(θ) o By measuring θ and using the given value of λ, you can use this equation to calculate the distance between rows of pits.

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Activity Procedure: 1.Have each student group use tape to attach the CD and DVD next to each other on the edge of a table (see image). Face the label sides away from the table. Make sure that the centers of the CD and DVD are placed on the table edge. 2.Place a piece of white paper on the table, and align it along the CD. 3.Students will use the protractors to measure diffracted laser beam angles; protractors are lifted off the table using spacers (located at position D in image). The spacers create a distance between the protractor and the table, and thereby allow the laser beam to go in the space between the sheet of paper and the protractor. 4.Remind students to make sure no one is in the path of the diffracted laser beams, and never shine the laser pointers in anyone's eyes! Estimating the Storage Capacity of a CD/DVD ctivities/uoh_diffraction/uoh_diffraction_activity1.xml

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Activity Procedure: 5.Have students turn on the laser pointers, and direct the beams towards their CDs. Align the beam with the 90° mark and the center of the protractor. The laser beam should be aligned with the normal of the CD surface (perpendicular to the CD). Students may need to adjust their laser pointers slightly before seeing diffraction patterns shown in the image. 6.When the incident and diffracted beams are clearly visible, direct students to measure the angles of the diffracted beams (the angle between the incident beam and diffracted beam) and record them in their worksheet tables. Remember that angles are measured from the normal (the 90° mark on the protractor). It might be easier for students to mark the beam positions on the white sheet of paper with a pencil and then measure the angle using their marks. Estimating the Storage Capacity of a CD/DVD s/uoh_diffraction/uoh_diffraction_activity1.xml

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Assessment: o Have students complete and hand in the Estimating Storage Capacity Worksheets. Examine their numerical results to see how well they understood the concepts. The results for the spacing ("d") might vary, but should be within a reasonable range.Estimating Storage Capacity Worksheets Activity Extension (Optional): o Extend the activity by varying the angle of incidence. The activity described uses an incoming laser beam that is perpendicular to the surface (such that the angle of incidence is zero). If the angle of incidence is not zero, the diffraction equation from above generalizes to: d(sin(θ i )+sin(θ m ))=mλ where θ i is the angle of incidence. Note that if θ i is set to zero, we get the equation outlined above. In the extended activity, have students measure the angle of incidence in addition to all other quantities described above. Estimating the Storage Capacity of a CD/DVD

SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Teaching tips: o Emphasize the science concepts, vocabulary, and engineering connection; reinforce these throughout the activity. o It’s important to line up the edge of the table along the diameter of the CD. The center of the protractor should be lined up midway between the center and the rim of the CD. o The angles are measured from the normal. For calculations, have students make sure their calculators are set to enter angles in degrees. o Emphasize the safety of lasers: Never point lasers directly towards other people. Be especially careful not to point to lasers towards someone's eyes. Estimating the Storage Capacity of a CD/DVD

Activity Takeaways Teambuilding skills o Working together on this investigative activity, collecting data, performing calculations and analyzing results Engineering skills o Engineering Research and Analysis : gathering results, analyzing data, relating results to real world engineering and technology that students may use all the time. SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Encouragement through hands-on learning o Students learn about technology that they may use all the time through hands-on investigation. Motivation through having fun o Introduce the activity as a fun learning experience!

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