![]() This reduces the chances of damage and is why CDs and DVDs are popular choices for our society.ĭescribe the concepts of diffraction and interference in CDs or DVDs.Īns: In CDs or DVDs, the discs themselves act as the diffraction gradient for the laser beam. This is better in comparison to cassettes for example, that contains physical contact between the player and the tape. Compared to other means of storage CDs and DVDs are used by focusing laser beams onto the disc, since light is the only thing that touched the disc in theory it never wears out. The bumps act as a diffraction grating so that when the laser beam is reflected the pattern contains a binary code that is read by pickups and transmitted or amplified.Īns: CD’s and DVD’s impact our society by changing the way we store information. The shiny part of the disk contains bumps that reflect the focused laser beam. Next, measure the height from where the laser hits the DVD and record it.Īns: CDs and DVDs work by having lasers focused on the shiny part of the disc.For a DVD only one dot will appear in the diffraction pattern, draw the pattern on the paper and measure the distance from the DVD to the dot.Just like the CD, when focusing the laser on the DVD it is important to make sure that the light hits the DVD at a 90-degree angle.Again while setting up be sure to tape the paper and the DVD onto the textbook and the table. The setup for a DVD is similar to that of the CD, the difference is the disk.Step 3: Recording data to determine the width of tracks in a DVD. Next, draw/mark the diffraction pattern on the paper and measure the distance between the two maxima.While the laser is focused on the CD measure the height at which the laser’s light hits the CD and record it. For a CD the diffraction pattern would appear on the paper, this is why the lab is set up this way.This helps ensure that the laser is hitting the CD at a 90-degree angle. When focusing the laser onto the CD it is very important that the laser is parallel to the table or that while it is focused on the CD its reflection is directly on the source of the laser.Set up the lab according to Figure 2, making sure that the CD and the paper are taped onto the corresponding surfaces.Step 2: Recording data to determine the width of the tracks in the CD. After marking the pattern use a ruler to measure the distance between maxima and record the values as your ∆x value. Focus the laser through the diffraction grating and while it is on, mark and draw the diffraction pattern onto the paper.Measure the distance from the diffraction grating to the textbook, this will be your L value.Before you begin, record the number of slits in the diffraction grating, this will be your d value.The first thing to do is to set up the lab according to the diagram in Figure 1, make sure the papers are taped onto the textbook and the table.Step 1: Recording data for determining wavelength of the laser.įigure 1: This is the set up for gathering information to determine the wavelength of the Red Laser source -Diffraction grating(s) of known spacingįor this lab, we will undergo three main steps to gather the information we will need to determine the wavelength of the laser and the groove spacing for the CD and DVD The difference in widths of tracks is due to the fact that both the CD and DVD have different storage capabilities therefore the spacings are different. In addition to this, the width of tracks for a CD is approximately 1.6 μm and for the DVD it is 0.74 μm. The wavelength of the laser is within the range of the wavelength of its colour, which is 630nm to 650nm. We will demonstrate the diffraction patterns formed when the laser passes through the gratings. The purpose of this lab is to experimentally determine the wavelength of a laser, and the widths of tracks on a CD & DVD. We calculate the track spacing for the CD to be 1.5 μm and the track spacing for the DVD to be 0.7 μm and compare our results for the spacing. Using this information we will then determine the track spacing for a CD and DVD. Using the formula λ = ∆x L / d, we will determine the wavelength of a red laser to be 641nm.
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