Section Assessment Item4

COMPARING  AND CONTRASTING

Helium-neon laser:a helium–neon laser or HeNe laser, is a type of gas laser whose gain medium consists of a mixture of 85% helium and 15% neon inside of a small bore capillary tube, usually excited by a DC electrical discharge. The best-known and most widely used HeNe laser operates at a wavelength of 632.8 nm, in the red part of the visible spectrum. (GAS)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Cloudy Ice Cubes:The main reason is that the (hopefully) crystal-clear water you pour into the ice trays is not as pure as it seems, containing small amounts of (hopefully) harmless suspended minerals and sediment.

Because all objects freeze from the outside in, the center of the cube is the last to solidify. Water free of minerals and impurities freezes first, pushing the cloudy parts containing the sediment (and tiny trapped air bubbles) toward the center. The result is a harmless (but not particularly photogenic) ice cube clouding.

Not only do ice cubes cloud in the freezer, but they also shrink noticeably after about a week or two due to sublimation, the term used for evaporation directly from the solid to gas phase.                                                                                                                                                                                                                                                                                                      Bronze:Bronze is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon. These additions produce a range of alloys that may be harder than copper alone, or have other useful properties, such as stiffness, ductility, or machinability.                                                                                                                                                                                                                                                                                                                                                  Ginger Ale: Ginger ale commonly contains carbonated water, sugar or HFCS, and artificial or natural ginger-flavour.(GAS)                                                                                                                                                                                                                                                                                                                COMPARE: All three solutions are gas except Bronze that is a solid.                                                             CONTRASTING :Ginger ale is a liquid gas but helium-neon laser is a gas, gas. Cloudy ice cubes is a solid,gas but Bronze is a solid.