What it shows: The wave nature of light limits our ability to see the very small. Application of the Rayleigh limit of resolution tells us that the size of the smallest objects one can resolve under a microscope is approximately equal to the wavelength of light. The optical limits of a microscope are demonstrated as one attempts to resolve 1 μm diameter spheres (about twice the wavelength of light) — one sees spots of light surrounded by diffraction rings rather than sharply defined spheres, similar to the 3rd image (from: Cagnet/Francon/Thrierr, Atlas of Optical… Read more about Microscope Resolution
What it shows: Two bodies, rotating about each other, rotate about their common center-of-mass (COM). The COM exhibits uniform motion (or none at all) regardless of what the two bodies are doing.
How it works: The "bodies" are 4-1/2" diameter acrylic disks that float on a cushion of air on a large air table.1 Presently we have three versions ready to go. (1) The first version has two disks connected by means of a 12"- long plastic ruler. A large "dot" at the center of the ruler marks the COM. The disks can be made to simply spin about… Read more about Air Table Center-of-Mass Motion
What it shows: A voltage pulse, injected into a long coaxial cable, will travel down the length of the cable and undergo a reflection at the other end. The nature of that reflection depends on how the cable is terminated at the other end. Shorting the cable at the far end produces an inverted reflection. With no termination (an "open" end), the reflected pulse is not inverted. When the impedance of the termination matches that of the cable, there is no reflection.
This demonstration allows you to compare chalk’s compressive strength with its tensile strength.
How it works:
We use railroad chalk, which although being softer and harder to work, is nice and big and easy to see. A sample is placed in each of the two types of testing assembly (details in Setting it Up), and loads carefully applied. Railroad chalk has a tensile strength of 195kNm-2 ± 30kNm-2 (a load of 2.5 to 3.5kg) and a compressive strength of 500kNm-2 ± 65kNm-2 ( a load of 7 to 9kg). … Read more about Fracture Strength of Chalk
A neutral system of charges is rearranged...charge measured on one part is equal and opposite to the charge on another part. In that respect, this demonstration is not much different from the " 3 Sig Figs" demo in which voltage measurements are used. Conservation of charge is typically introduced in the first few lectures of an E&M course, before the concepts of voltage and capacitance are discussed. If voltage is the… Read more about Conservation of Charge to 2 Sig Figs
Like visible light, invisible infra-red radiation can be refracted by lenses to produce an image on a screen. Indeed, a slide projector designed for visible light is used as the imaging device; a heat- sensitive screen makes the invisible IR image visible.
How it works:
Our IR source is a 1000 watt "lantern slide" projector 1 from which we have removed the special heat-absorbing glass in the condenser assembly. The slide to be imaged is some kind of lettering, like the name of the course (Science A-29… Read more about Infra-Red Projector
Lithium, sodium, and potassium undergo reactions with water.
Two liters of warm water in large pyrex vessel, covered with fine mesh stainless steel screen, is on a stool close by in-floor vent hood. Add a few drops from the phenolphthalein indicator bottle, and a few drops of 1M hydrochloric acid if the warm tap water turns pinkish.
Video camera is clamped to the stool leg, and pointed at the bottom of the beaker. Before class, frame the shot and focus on the center of the beaker.