Light bulb, lifetime

Light bulb lifetimes, and the corresponding Gaussian curve, are characterized by two parameters. The arithmetic mean, x—also called the average—is the sum of the measured values divided by n, the number of measurements ... 

Tlie failure rate per year, Y, of a coolant recycle pump has a log-normal distribution. If In Y luis mean, -2, and variance, 1.5, find P(0.175 < Y< 1). Tliree light bulbs (A, B, C) are coiuiected in series. Assume tliat tlie bulb lifetimes are noniially distributed, witli tlie following means and standard deviations. 

The lifetime of a tungsten filament in an incandescent light bulb depends a great deed on the grain size of the wire used to make the filament. W-metal powder is pressed into a bar at pressures which ensure that the density is as... 

In his lifetime, Thomas Alva Edison patented 1,093 inventions, but the incandescent light bulb is generally regarded as his most famous invention. On October 21,1879, 29-year-old Thomas Edison demonstrated the first incandescent lamp in Menlo Park, NJ. The bulb burned for 13.5 hours. The chemistry of the components of this lighting device are essential to its incredible success. 

In Figure 4-1, s = 94.2 h. A set of light bulbs having a small standard deviation in lifetime is more uniformly manufactured than a set with a large standard deviation. 

Fig. 2.8. Oxygen concentration versus filament lifetime for an exposed light bulb filament burning in an inert atmosphere. By noting how long the light bulb stays lit, a reasonable estimate of the oxygen plus moisture impurity level can be obtained. These data correspond to an A/C No. 63 bulb filament run with 10 V potential and a gas flow rate of 1.1 L/min.

Tliree light bulbs (A, B, C) are comiccted in series. Assume tliat the bulb lifetimes are noniially distributed, vviUi tlie following means and standard deviations. 

This diagram of a typical LED indicator light shows how small the actual LED is. Although the average lifetime of a small light bulb is 5-10 years, a modern LED should last 100 years or more before it fails. Illustration by Hans Cassidy. Courtesy of Gale Group. 

A random variable is an observable whose repeated determination yields a series of numerical values ( realizations of the random variable) that vary from trial to trial in a way characteristic of the observable. The outcomes of tossing a coin or throwing a die are familiar examples of discrete random variables. The position of a dust particle in air and the lifetime of a light bulb are continuous random variables. Discrete random variables are characterized by probability distributions P denotes the probability that a realization of the given random variable is n. Continuous random variables are associated with probability density functions P(x) P(xi)dr... 

Before the invention of the transistor in 1947 at Bell Laboratories by John Bardeen, Walter H. Brattain, and William B. Shockley, vacuum tubes were the workhorse of electronics. Vacuum tubes were bulky and fragile, required high voltage (>45 V) and a heater current to operate, and had lifetimes comparable to electric light bulbs. It is certainly no exaggeration to say that the transistor made possible modem solid-state electronics. Transistors serve much the same fimction as the old vacuum tubes but are much smaller, mgged, operate on low voltages, and have virtually infinite lifetimes. 

A 13-W fluorescent light that fits in a standard screw-in socket provides the same light as the 60-W bulb it replaces. The expected lifetime of the fluorescent lamp is 10 000 h, whereas that of the incandescent bulb is 750 h. The fluorescent light is more expensive than the incandescent bulb but saves a great deal of electricity and money over its lifetime. 

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