How do batteries store and discharge electricity? —D. DODDS, DETROIT
Kenneth Buckle, a visiting scientist at the Center for Integrated Manufacturing Studies at the Rochester Institute of Technology, provides this answer:
When connected to a load like a lightbulb, a typical battery undergoes chemical reactions that release electrons, which travel through the bulb and are then reabsorbed by the battery. (Devices that store mechanical energy also exist, but the most common batteries, such as those used in flashlights and remotes, hold energy in chemical form.) Inside is at least one galvanic cell, which produces between zero and several volts, depending on its chemistry. In a car battery, six cells, each contributing two volts, are connected in series to make a 12-volt battery.
All electrochemical cells consist of two electrodes separated by some distance. The space between the electrodes is filled with an electrolyte, a liquid or solid containing charged particles, or ions. One electrode—the anode—emits negatively charged electrons. The other—the cathode—receives them. Chemical differences between the two electrodes create an energy difference, or potential, that moves electrons from the anode to the cathode via the electrolyte. For example, the lead-acid cell uses a lead oxide cathode, a lead anode and a sulfuric acid (liquid) electrolyte.
In this case, sulfuric acid creates an environment that stretches the chemical bonds of the lead and lead oxide, so oxidation and reduction reactions occur simultaneously. In the reduction reaction the acid strips the oxygen from the leadoxide cathode and replaces it with sulfate. The oxide ion then combines with hydrogen (from the acid) and forms water. In oxidation the sulfuric acid coaxes two electrons away from the lead and then latches on to form lead sulfate. If the battery is attached to a load, the electrons that the sulfate replaces travel out of the cell and into the load, creating an electric current.
A galvanic cell can continue to discharge electrons until either or both electrodes run out of reagents, the compounds that drive the oxidation/reduction reactions. In a nonrechargeable battery the chemical reaction that created the energy is not easily reversible, and when the reagents run out the cell is unusable. In a rechargeable battery, such as the lead-acid cell, the reaction is reversible, meaning that an external source of direct electric current can force the electrons to flow from the cathode to the anode until the cell is recharged.
Does damp weather make arthritis pain worse? —C. LEVY, FALLS CHURCH, VA.
Donald A. Redelmeier, a professor of medicine at the University of Toronto, explains:
Despite the commonly held notion that dampness contributes to joint aches, decades of medical research show no objective relation between arthritis severity and weather.
Dampness, decreases in barometric pressure and high humidity are characteristics that some people believe contribute to flares in arthritis pain, but similar environmental changes experienced during other situations do not seem to affect sufferers one way or the other. For instance, arthritis patients do not experience dramatic increases in symptoms when bathing or swimming. Patients easily tolerate greater swings in pressure during a plane ride than would occur during a storm.
Still, no past study investigating the link between weather and arthritic pain is flawless; research has neither totally ruled out nor established a connection. Evidence of a causal link requires dispassionate observation wherein neither clinicians nor patients know what exposure is active. Clinicians and patients would have to ignore weather—a difficult task.
Studies suggest people see patterns even where none exist. By chance, some rainy days will be followed by pain, entrenching the belief in a connection. Ultimately, such beliefs reveal more about the workings of the mind than those of the body.
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