Lightbulb

Throughout this text, we will use the SI unit joule (J)> defined in Appendix 1, to express energy. A joule is a rather small quantity. One joule of electrical energy would keep a 10-W lightbulb burning for only a tenth of a second. For that reason, we will often express energies in kilojoules (1 kj = 103 J). The quantity h appearing in Planck s equation is referred to as Planck s constant... 

Use a Flinn C-Spectra to view an incandescent lightbulb. What do you observe Draw the spectrum using colored pencils. 

With the room lights darkened, view the light using the Flinn C-Spectra . The top spectrum viewed will be a continuous spectrum of the white lightbulb. The bottom spectrum will be the absorption spectrum of the red solution. The black areas of the absorption spectrum represent the colors absorbed by the red food coloring in the solution. Use colored pencils to make a drawing in the data table of the absorption spectra you observed. 

Wait several minutes to allow the incandescent lightbulb and the spectrum tubes to cool. 

Follow your teacher s instructions on how to dispose of the liquids and how to store the lightbulb and spectrum tubes. 

Position the 150-watt lightbulb about 15 to 20 cm over the top of the solar pond model. Turn on the light. Press ENTER on the calculator to begin collecting data. After about 6 to 8 minutes, turn off the lightbulb and move it away from the solar pond model. Do not disturb the experiment until the calculator is finished with its 30-minute run. 

Interpreting Graphs Describe the shape of each curve in the graph of time versus temperature before and after the lightbulb was turned off. Explain the significance of the difference. 

Applying Concepts Why does the graph of time versus temperature decrease more rapidly near the surface when the lightbulb is turned off ... 

This situation can be fully developed by slightly improving the previous experiment. Consider that instead of being connected to the lightbulb, the detector is linked to a fast shutter, as shown in Fig. 5. 

From this reaction we can see that, in order for a water molecule to gain a hydrogen ion, a second water molecule must lose a hydrogen ion. This means that for every one hydronium ion formed, there is also one hydroxide ion formed. In pure water, therefore, the total number of hydronium ions must be the same as the total number of hydroxide ions. Experiments reveal that the concentration of hydronium and hydroxide ions in pure water is extremely low—about 0.0000001 M for each, where M stands for molarity or moles per liter (Section 7.2). Water by itself, therefore, is a very weak acid as well as a very weak base, as evidenced by the unlit lightbulb in Figure 10.9a. 

The elemental iron and copper ions need not be in physical contact in order for electrons to flow between them. If they are in separate containers but bridged by a conducting wire, the electrons can flow from the iron to the copper ions through the wire. The resulting electric current in the wire could be attached to some useful device, such as a lightbulb. But alas, an electric current is not sustained by this arrangement. 

Politicians in the United States have proposed taxing individuals and industries for the amount of C02 they emit. Collected revenue would be placed in a trust fund to subsidize consumers who purchase energy-efficient devices, such as fluorescent lightbulbs and high-gas-mileage automobiles. Discuss the pros and cons of such a proposal. What modifications might you propose ... 

He decided that the material the world needed most was a synthetic shellac to replace the natural shellac produced from the resinous secretions of the lac beetle native to southeastern Asia. At the time, shellac was the optimal insulator for electrical wires. Ever since Edison s 1879 invention of the incandescent lightbulb, miles of shellac-coated metal wire were being stretched across the land. The supply of shellac, however, was unable to keep up with demand. 

A lot of watts means that a lot of energy is being consumed quickly. A 100-watt lightbulb, for example, consumes 100 joules of energy each second, and a 40-watt bulb consumes only 40 joules each second. 

How much money would you save per hour by replacing a 100-watt incandescent lightbulb with an equally bright 20-watt fluorescent bulb Assume the cost of electricity to be 15 cents per kilowatt-hour. 

Then calculate the cost of running the 20-watt lightbulb for 1 hour, understanding that 20 watts is the same as 0.02 kilowatt ... 

The savings for each hour is the difference 1.5 cents minus 0.3 cents, which equals 1.2 cents per hour. This may not sound like much, but if 50 million households in the United States changed just one of their lightbulbs from a 100-watt incandescent to a 20-watt fluorescent, then the total annual savings would be on the order of 1.2 billion dollars. 

---