Author: Lou Bloomfield

How does a halogen lamp get so hot?

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How does a halogen lamp get so hot?

Like all incandescent bulbs, a halogen lamp creates its light as visible thermal radiation from an extremely hot tungsten wire. In fact, the wire in a halogen lamp is allowed to get even hotter than the one in a normal bulb. But while the glass envelope of a normal bulb gets only moderately hot during use, the glass envelope of a halogen bulb gets extremely hot. That’s because the halogen bulb is using a chemical trick to keep tungsten atoms from getting away from the filament. Each time one of those tungsten atoms tries to leave, it’s picked up by halogen molecules inside the glass envelope and returned to the filament. These halogen molecules can even pick the tungsten atoms up off the glass envelope and return them to the filament, but only if the glass envelope is allowed to get extremely hot. That’s why the glass envelope of the halogen bulb is allowed to run so hot—if it weren’t, it would accumulate the tungsten atoms permanently and it would darken. And since the tungsten atoms wouldn’t be returned the filament, the filament wouldn’t last as long.

Our problem concerns temperature. At different temperatures, solubility of compo…

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Our problem concerns temperature. At different temperatures, solubility of compounds varies. If we extract water from a pond at two degrees Celsius and then test it at room temperature, our reading isn’t going to be accurate. On the other hand, it isn’t practical for us to perform out tests outside. The substances we are testing are nitrites, nitrates, ammonia, pH, hardness, oxygen level, phosphates, temperature, and ORP. — J&E, Missouri

If you collect pond water at 2° C and then bring it into a room at 20° C, there will be a few subtle changes in the water’s contents. While the amounts of various dissolved materials can’t change unless atoms move in or out of the water, how they interact with one does change somewhat with temperature. I would be very surprised if anything that’s dissolved in that pond water comes out of solution when you warm it to room temperature, so if all you want to do is to determine the concentrations of various dissolved materials, go ahead and do it at room temperature. You might have to be careful with dissolved gases, because it’s relatively easy for gas molecules to enter or leave the pond water without your noticing that it’s happening, but the nitrites, nitrates, hardness, and phosphates aren’t going anywhere. Ammonia can leave as a gas, so you should be a little careful with it. I don’t know enough about ORP (oxidization reduction potential) to say anything about it. But you’ll have to be very careful with oxygen concentration because you can modify this just by pouring the water through air and making bubbles.

However, to be sure that the contents of the pond water are interacting with one another just as they were in the pond, you should cool the water back down to 2° C before making any measurements. This is particularly important for pH measurements, since water’s pH decreases slightly with increasing temperature.

What is pH and why is it so important to my garden pond and spa?

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What is pH and why is it so important to my garden pond and spa? — NW, California

pH is a measure of the concentration of dissolved hydrogen ions in water. When a hydrogen atom loses an electron and becomes a hydrogen ion—a proton—it can dissolve nicely in water. Actually, this proton sticks itself to the oxygen atom of a water molecule, producing a hydronium ion (H3O+) that is then carried around by shells of water molecules. The higher the concentration of hydrogen (or hydronium) ions in water, the lower the water’s pH. More specifically, pH is negative the log (base 10) of the molar hydrogen ion concentration. That means that water with a pH of 6 has ten times as many hydrogen ions per liter as water with a pH of 7.

Pure water naturally contains some hydrogen ions, formed by water molecules that have spontaneously dissociated into hydrogen ions (H+) and hydroxide ions (OH–). Pure water has enough of these hydrogen ions in it to give it a pH of 7. But if you dissolve acidic materials in the water, materials that tend to produce hydrogen ions, the pH of the water will drop. If you dissolve basic materials in the water, materials that tend to bind with hydrogen ions and reduce their concentration, the pH of the water will rise. Water with too many or too few hydrogen ions tends to be chemically aggressive and we do best in water that has a pH near 7.

How do you make an energy converter to convert water into energy?

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How do you make an energy converter to convert water into energy? — SB

I’m afraid that there is no simple way to convert water into energy. People have been trying to use fusion to extract the nuclear energy stored in the hydrogen nuclei in water. But while billions of dollars have been spent on research, there is no viable scheme for this process for controlled fusion in sight. The stars are powered by hydrogen fusion, but people on the earth aren’t likely to be using it as a source for peaceful energy any time soon.

My husband and I watch Star Trek often. He says that travel at warp speeds (fast…

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My husband and I watch Star Trek often. He says that travel at warp speeds (faster than the speed of light) is impossible and that Einstein’s theories prove it. Is this true? — JL, Las Cruces, NM

I’m afraid that travel at or above light speed is simply impossible and that “warp speed” travel is just a Hollywood fantasy. Einstein’s special relativity forbids objects with mass from reaching or exceeding the speed of light and even if there were some way to travel vast distances in less time than it would take light to cover those distances, but without actually traveling at light speed, such travel would violate some important principles of causality—you would be able to meet your own grandparents as children and that sort of thing.

One of the reasons that Hollywood ignores real physics so often is that real physics is almost wilder than fiction. Suppose that you decided to travel to a star 5 light-years away from the earth and that you have a starship that can almost reach the speed of light (another nearly impossible thing, but let’s ignore that problem). If you travel to the star at almost the speed of light, make one loop around it, and head right back to earth, I will have aged 10 years while waiting for you to return. However, you will only have aged days or weeks, depending on just how close you came to the speed of light. During the trip, we will have disagreed on many physical quantities, particularly the times at which various events occurred and the distances between objects. The mixing of time and space that occur when two people move rapidly relative to one another would be so disorienting to movie or television viewers that Hollywood ignores or simplifies these effects.

How does dry ice work to freeze things?

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How does dry ice work to freeze things? — JH

Solid carbon dioxide or “dry ice” sublimes into gaseous carbon dioxide at a temperature well below 0° C. Since it takes energy to separate the molecules of carbon dioxide from one another, the dry ice absorbs heat as it sublimes and takes that heat out of any warmer objects nearby. Those nearby objects become colder and colder as the heat leaves them and eventually they begin to freeze.

How do conductors and insulators work?

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How do conductors and insulators work? — SN, Beverly, MA

Because of the quantum physic that dominates the behaviors of tiny objects in our universe, electrons can’t travel in every path you can imagine; they can only travel in one of the paths that are allowed by quantum physics—paths that are called orbitals in atoms and levels in solids. When a material is assembled out of its constituent atoms, those atoms bring with them both their electrons and their quantum orbitals. These orbitals merge and blend as the atoms touch and they shift to form bands of levels in the resulting solid. The electrons in this solid end up traveling in the levels with the lowest energies. Because of the Pauli exclusion principle, only one indistinguishable electron can travel in each level. Since there are effectively two types of electrons, spin-up and spin-down, only two electrons can travel in each level of the solid.

In a conductor, there are many unused levels available within easy reach of the electrons. If the electrons have to begin moving toward the left, in order to carry an electric current, some of the electrons that are in right-heading levels can shift into empty left-heading levels in order to let that current flow. But in an insulator, all of the easily accessible levels are filled and the electrons can’t shift to other levels in order to carry current in a particular direction. While there are empty levels around, an electron would need a large increase in its energy to begin traveling in one of these empty levels. As a result, the electrons in an insulator can’t carry an electric current.

What role do gravity and inertia play in making a roller coaster work?

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What role do gravity and inertia play in making a roller coaster work? — B

Gravity provides the energy source for a roller coaster and inertia is what keeps the roller coaster moving when the track is level or uphill. Once the roller coaster is at the top of the first hill and detaches from the lifting chain, the only energy it has is gravitational potential energy (and a little kinetic energy—the energy of motion). But once it begins to roll down the hill, its gravitational potential energy diminishes and its kinetic energy increases. Since kinetic energy is related to speed, they both increase together.

At the bottom of the first hill, the roller coaster has very little gravitational potential energy left, but it does have lots of kinetic energy. The roller coaster also keeps moving, despite the absence of gravitational potential energy. You can view its continued forward motion as either the result of having lots of kinetic energy or a consequence of having inertia. Inertia is a feature of everything in our universe—a tendency of all objects to keep doing what they’re doing. If an object is stationary, it tends to remain station. If an object was moving forward at a certain speed, it tends to keep moving forward at a certain speed. Inertia tends to keep the roller coaster moving forward along the track at a certain speed, even when nothing is pushing on the roller coaster. While the roller coaster will slow down as it rises up the next hill, its inertia keeps it moving forward.

Our area has been flooded recently (Kentucky, Indiana) by about 15 inches of rai…

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Our area has been flooded recently (Kentucky, Indiana) by about 15 inches of rain. How is it that the Ohio River has risen so many feet and not just 15 inches? — RK

The Ohio River is carrying water collected by vast areas surrounding the river and this accumulated volume of water is enough to raise the river’s level by many feet. Similarly, if you collected all the rain water that accumulated on your yard and poured that water into a bathtub, the level of water in the bathtub would rise far more than 15 inches.

Can an object be heated no hotter than the temperature of the flame beneath it? …

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Can an object be heated no hotter than the temperature of the flame beneath it? For example, if the temperature of a candle flame is 1770° C and the melting point of the solid being heated above it is 1800° C, would the solid ever melt if the flame were held under it long enough? — MR, Ohio

The answer is a qualified no. Heat always flows from hotter objects to colder objects, so the solid can’t get any hotter than the flame that’s heating it. But this observation is stems from the laws of thermodynamics, particularly the second law of thermodynamics. Unlike Newton’s laws of motion, which are rigid, inviolable laws that are never, even violated in our universe, the second law of thermodynamics is a statistical laws—it says that certain events are extremely unlikely but doesn’t say that they are truly impossible. The flow of heat from hotter to colder is a statistical law, not a rigid mechanical law. So it is possible, although extraordinarily unlikely, that heat can flow from the 1770° C flame to the 1799° C solid and warm that solid all the way to 1800° C. However, for any reasonable sized solid (say, more than 10 atoms), the possibility of this occurring is going to be so unbelievably small as to be ridiculous. It’s as unlikely as taken a crystal wineglass that has been crushed into dust and then dropping it on the floor and having the impact reassemble the wineglass into its original pristine form. The laws of motion don’t forbid such as fantastic result, but it sure would be unlikely. I’ve tried it several times myself, without success. But then, you’re not going to be able to melt your solid with a not-hot-enough flame, either. You’d have to wait a few ages of the universe just to have that solid climb a tiny fraction of a degree above the temperature of the flame. For 20 degrees… forget it.