Intro Nanoscience and Technology
Intro Nanoscience and Technology ENGR 250
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This 7 page Class Notes was uploaded by Waino Bogisich MD on Monday September 21, 2015. The Class Notes belongs to ENGR 250 at University of Virginia taught by John Bean in Fall. Since its upload, it has received 22 views. For similar materials see /class/209724/engr-250-university-of-virginia in Engineering and Tech at University of Virginia.
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Date Created: 09/21/15
ENGR250 Ripple Tank Labs Guidelines amp Reporting Form rev 92608 Student Name printed Signature Student Name printed Signature Student Name printed Signature First download and review the manual provided by the ripple tank s manufacturer Pasco The rst ten pages ofthat manual provide general information on the equipment and its setup The remaining pages suggest experiments forthe ripple tank Copies of that manual will be in the lab so you don t have to print it out From that manual and our experience we suggest this set up procedure Step 1 Con gure the system as shown on the rst page ofthe manual The rectangular LED light source bar placed high on the rod which is screwed into the tank Its LED hole should be overthe approximate center ofthe tank pointing downward The ripple generator the electronics box is on the separate rod base The generator should overhang the tank but not quite touch it It should be perpendicular to the tank with its center point at about the center ofthe tank s edge The LED light source should be plugged into the ripple generator and the ripple generator plugged into an AC power source Step 2 Carefully level the tank using the spirit level we ve added to the kit by adjusting the screwin feet at the bases ofthe tank s three legs Step 3 Find the drain that hangs down from one corner of the tank and gure out how to open and close it Then close it Step 4 Fill the tank with the recommended 800 ml of water Step 5 Place the now empty measuring cup under the tank drain so that you can later adjust the water level in the tank Learn how to generate high quality plane straight waves Step 1 Attach the long Plane Dipper bar to the wave generator item 1 page 7 ofthe manual Its two rods snap into receptacles on the generator unit Step 2 Adjust the generator so the bar is parallel to the tank s edge use the ruler to even up the separation ofthe bar from the tank s edge Step 3 Using the two red knobs on the generator box lower the bar so that it just touches the water along its whole length Most likely this will require adjusting the tilt of the generator using the tilt red knob the one in the corner ofthe generator box see the manual page 8 Repeatedly use the lift red knob lifting then lowering the bar out ofthe water until you are sure that it is contacting the water all along its whole edge simultaneously Leave the bar so that it is pulling UP a meniscus ofwater along its length Step 4 Set the phase switch so that the bar is lifted up and down parallel to the water rather than rocking back and forth This SHOULD be the switch s up position but it is reversed on at least one ofour units you ll be able to check this in the next step Step 5 Turn on the wave generator electronics Use the wave frequency and amplitude knobs to learn how to make waves that give simple clear images on the wave tank screen try this with and without using the strobe As you turn up the amplitude you ll nd that the wave image initially improves But ifthe amplitude gets TOO high the image will deteriorate becoming more complicated and irregular as secondary harmonic waves are produced Further you ll find that at low frequencies below 6 Hz you ll need higher amplitudes than will be optimum at higher frequencies When you think you ve mastered basic wave generation have the TA certify this by signing here TA s signature Our Experiment 1 Diffraction Class s lecture 2 Manual page 19 Follow the general instructions for the experiment as called out beginning on page 19 ofthe manual Demonstrate the onset of diffraction when the wavelength ofthe wave exceeds the size of the gap Do this either V th xed barriers changing the wavelength of the wave V th xed wavelength varying the gap by moving the barriers Try both techniques Diffraction means that it is impossible to focus or constrain a wave into a beam narrower than its wavelength via lenses or shadow masks In fact as you should have seen if you try this the beam instead expands rapidly as a circular wave This is the reason microfabrication technologies which are based on light micro photography cannot produce nanoscale objects This failing drives drives nanoscience s search for alternative selfassembly techniques When you think you can clearly demonstrate the onset of diffraction have the TA certify by signing here TA s signature Our Experiment 2 Scattering Class s lecture 2 not in manual Remove the barriers from experiment 1 In their position instead stand up the three small white tubes sections of 12 plastic pipe in a widely space row You ll see waves bouncing offthe cylinders But the important question is how MUCH ofthe incoming wave s energy is being redirected scattered To estimate this look behind the cylinders Are there wave shadows behindthe cylinders ie regions ofalmost still wavefree water These cylinders are hard and thus absorb very little wave energy 80 if wave energy is missing behind the cylinders ie there are shadows that energy must be going elsewhere which is to say it IS being scattered Set up incoming waves of varied wavelength At a wavelength that does not leave shadows try instead putting in one of the big rings the ones split in two halves Does it have a shadow How does scattering change ie how does the degree of shadowing change From this you should be able to gure out why sun block manufacturers are grinding their UV absorbing materials into nanoparticles to prevent them from scattering visible light which would make them appear white When you think you can clearly demonstrate the onset of scattering have the TA certify by signing here TA s signature Our Experiment 3 Standing Waves Class s lecture 3 not in manual Remove all objects from the tank Remove the long Plane Dipper wave generator bar and replace it with ONE of the Standard Dippersquot manual page 4 item 7 Move the wave generator so that dipper is as close to the center of the tank as possible without having its ring stand touch the tank Place one ofthe rings around that dipper the rings are cut in half so that you can place them without having to move the dipper Get the dipper as close to the center of the ring as you can Using the strobe start at a very low frequency eg 4 Hz and then gradually increase the frequency reducing the amplitude to get the sharpest wave at each frequency At certain frequencies you will observe sharp strong standing waves Write down their frequencies At these frequencies a certain number of wavelengths fit exactly into the ring The wavelength ofan ideal wave wave velocity frequency From this can you take your frequencies above and gure out how many wavelengths were tting into the ring for each NOTE your waves may NOT be quite ideal with waves ofdifferent frequencywavelength moving at different velocities that would complicate the answer The Pasco manual experiment 6 page 27 explores wave velocity changes How do things change if you change to the different size ring TA s comments signature From here on you get to make your own choices on additional experiments either ones called out in the manual or ones you think up for yourself Because this is the rst year we ve used the ripple tanks in the labs we are not sure what a reasonable number of eXperiments is for the two lab periods Our strong preference is that you take your time doing the eXperiments as well as you can fully testing all of the variables and behaviors If it then turns out that the eXpectation of 5 more eXperiments is too many no problem TIP ON THE MANUAL S EXPERIMENT 2 REFRACTION Refraction depends on the fact that water waves slow in shallower water the main subject of the manual s eXperiment 6 To emphasize this difference set the waterlevel so it just barely ows over the clear yellow shapes It helps to wipe a drop of surfactant the soap from the squeeze bottle over the yellow shape before you putit into the tank ADDITONAL POSSIBLE EXPERIMENTS Although it s not immediately relevant to nanoscience I am sure you ve been told that 1 Parabolas focus incoming plane waves of ALL frequencies to a single point This is the basis for re ecting telescopes 2 Waves moving outward from one of the focal point of an ellipse will refocus at the other focal point If you care to test either of these statements I ve added a pair of bendable drafting curves to the sets You can bend these into parabolas and ellipses using the patterns provided on the last page of this guide To gure out where the foci should be A parabola described by y ax2 has its focus at the point 0 14a An ellipse centered on the origin with semimajor and semiminor axes of a and b is described by the equation X232 y2b2 1 where for agtb the foci are at X sqrta2b2 Experiment 1 Your choice of other experiment called out in the manual Your choice title page number in manual TA s certification TA s signature Experiment 2 Your choice of another experiment called out in the manual Your choice title page number in manual TA s certification TA s signature Experiment 3 Your choice of other experiment called out in the manual Your choice title page number in manual TA s certification TA s signature Experiment 4 Your choice of another experiment called out in the manual Your choice title page number in manual TA s certification TA s signature Experiment 5 An experiment of your own invention Description TA s comments
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