COMMON MATERIALS AND OF fiCE SUPPLY PRODUCTS:POLARIZED SUNGLASSES AND RECHAR GEABLE BA TTERIES.

POLARIZED SUNGLASSES

How light waves interact with matter has been studied at great length throughout centuries. Sunlight and other light sources transmit light as waves at perpendicular angles to the direction of travel. In 1669, a Danish mathematician, Erasmus Bartholinus, performed the first comprehensive experiments concerning the interaction of light with transparent calcite crystals, which is considered the first account of polarized light waves. In 1932, Edwin Land developed a synthetic film of quinine sul- fate and iodine embedded in nitrocellulose and trademarked the name Polaroid. This material had a very interesting property. It allowed only light waves that were cohesive, or traveling in the same direction, to pass through the lens. In practice, this reduced the ambient light reaching the eye by more than 50 percent, making the material ideal for sunglasses. It also significantly reduced sun glare from objects by allowing only a frac- tion of the glaring light to pass through the lenses. Today, polarized sun- glasses are made by stretching an amorphous polymer of polyvinyl alcohol that aligns the molecules and sandwiching this layer between sheets of transparent material such as glass. These sunglasses are used in a variety of activities, such as driving, skiing, boating, and playing sports. Polarized sunglasses help reduce glare and filter out a significant amount of light without distorting images.

RECHAR GEABLE BA TTERIES

Many consumers are familiar with rechargeable batteries that are common in many everyday devices, such as cellular phones, laptop computers, and digital cameras. These batteries are constructed very much like a normal dry cell or alkaline battery. Typically, they contain nickel, cobalt, zinc, or cadmium and an electrolyte of potassium, sodium, or lithium hydroxide. The most common rechargeable batteries are based on a nickel/cadmium design with a cadmium anode and a nickel oxide cath- ode. These batteries operate very much like other batteries with one major difference. When the chemical reaction has been completed and no electron gradient exists between the anode and the cathode, these batteries can be recharged by an external current that reverses the flow of electrons from the cathode to the anode. This reestablishes the electron gradient between the two ends of the battery and allows the battery to be reused after charging is complete. This process can be repeated as many as 1,000 times before the batteries lose their ability to be recharged. Rechargeable batteries are not as new as you might think. The most common rechargeable battery is the lead-acid battery, which has been found in automobiles for the better part of a century. Rechargeable bat- teries undergo a reversible reaction, providing electrons to power devices and being recharged by reversing the chemical reaction to pump electrons back into the battery. Rechargeable batteries may leak when recharged, and the contents are harmful if swallowed and cause burns from the caustic electrolyte materials. As such, it is important to be sure that bat- teries are never connected improperly, short circuited, or exposed to high temperatures.