Author: Lou Bloomfield

Why does regular water freeze faster than salt water?

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Why does regular water freeze faster than salt water? — CD, Crown Point, IN

When salt dissolves in water, its individual sodium positive ions and chlorine negative ions are carried about by the water molecules. Each of these ions is wrapped in a solvation shell of water molecules. These solvation shells and the salt ions themselves interfere with the water’s ability to crystallize into ice. The ice crystals that form when salt water freezes rarely include the salt ions so the water molecules must abandon the salt ions in order to crystallize. Because of the attraction between the salt ions and the water molecules, and because of the loss of randomness that comes with forming pure ice crystals in the midst of salty water, you must lower the temperature of salt water below the freezing temperature of pure water before that salt water will begin to freeze into ice. When ice does begin to form, it will be relatively pure water crystals and the remaining water will become increasingly saltier. If you’re ever lost in the winter without a supply of fresh water, look for sea ice—even though it forms from salt water, it contains very little salt.

Can you tell me the difference in lifting power of helium versus hydrogen?

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Can you tell me the difference in lifting power of helium versus hydrogen? — FL, Napa, CA

A balloon experiences an upward buoyant force that’s equal in amount to the weight of the air it displaces. If that balloon is filled with helium or hydrogen, both of which have very low densities, then this upward buoyant force may be more than the balloon’s weight and the balloon may accelerate upward. Helium weighs a little more per cubic foot or cubic meter than hydrogen does, so replacing the helium with hydrogen will make it easier to float the balloon. A cubic foot of hydrogen weighs 0.0056 pounds less than a cubic foot of helium and a cubic meter of hydrogen weighs 89 grams less than a cubic meter of helium. Any weight saving made by replacing helium with hydrogen in your balloon can be viewed as extra lifting power. As you can see, the effect is small and hydrogen is a whole lot more dangerous than helium.

Why is an incandescent light bulb hotter than a fluorescent light?

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Why is an incandescent light bulb hotter than a fluorescent light? — TJ, Woodbridge, VA

An incandescent light bulb produces light by heating a small filament of tungsten to about 2500° C. At that temperature, the thermal radiation that the filament emits includes a substantial amount of visible light. But the filament also emits a great deal of infrared light (heat light) and it also transfers heat via conduction and convection to the glass bulb around it. When you put your hand near the bulb, you feel both the infrared light and the heat that has worked its way to the surface of the bulb. The bulb feels hot.

In contrast, a fluorescent lamp tries to produce light without heat. It collides electrons with mercury atoms to produce an atomic emission of ultraviolet light. This ultraviolet light is then converted to visible light by the layer of white phosphor powders on the inside of the lamp’s glass envelope. In principle, this whole activity can be performed without creating any thermal energy. However, many unavoidable imperfections cause the lamp to convert some of the electric energy it consumes into thermal energy. Nonetheless, the lamp only becomes warm rather than hot.

How does ammonia refrigeration work?

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How does ammonia refrigeration work?

There are actually two answers to this question. First, like the more modern chlorofluorocarbon (Freon) and hydrofluorocarbon refrigerants, ammonia (NH3 converts easily from a gas to a liquid near room temperature. If you squeeze ammonia to high density, it will release heat and convert to a liquid. If you let it expand to low density, it will absorb heat and convert to a gas. A compressor-based ammonia refrigeration unit makes use of that easy convertibility. First, it uses a compressor to squeeze the ammonia gas outside the refrigerator. The hot dense ammonia gas that leaves the compressor enters a condenser, where it releases heat to its surroundings and condenses to a cool ammonia liquid. This liquid enters the refrigerator and passes into an evaporator, where it’s allowed to expand into a gas and it absorbs heat from its surroundings. The gas then returns outside the refrigerator to repeat this cycle again and again.

But there is a second type of ammonia refrigerator that makes use of an absorption cycle—ammonia dissolves extremely well in cool water but not so well in hot water. In an absorption cycle refrigerator, a concentrated solution of ammonia in water is heated in a boiler until most of the ammonia is driven out of the water as a high-pressure gas. This hot, dense ammonia gas then enters a condenser, where it gives up heat to its surroundings and becomes a cooler liquid. The liquid ammonia then enters a low-pressure evaporator, where it evaporates into a cold gas. This evaporation process draws heat out the evaporator and refrigerates everything nearby. Finally, the ammonia gas must be returned to the boiler to begin the process again. That return step makes use of the absorption process, in which the ammonia gas is allowed to dissolve in relatively pure, cool water. The gas dissolves easily in this water and thus maintains the low pressure needed for evaporation to continue in the evaporator. The now concentrated ammonia solution flows to the boiler where the ammonia is driven back out of the water and everything repeats.

How can you run a clock off of a potato?

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How can you run a clock off of a potato?

The classic technique is to insert two dissimilar metal strips into the potato in order to build a simple battery. You can then run an electronic clock with the power provided by that battery. But the energy in that battery is coming from chemical reactions of the metals and not really from the potato. If you really want to use a potato as the power source for a clock, you should dry the potato out and burn it. You can use the heat of the fire to run a steam engine or to generate electricity.

How does a car horn work?

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How does a car horn work? — CP

While some modern car horns are actually specialized computer audio systems, the old-fashioned electromagnetic car horns are still common. An electromagnetic horn uses an electromagnet to attract a steel diaphragm and turns that electromagnet on and off rhythmically so that the diaphragm vibrates. In fact, it uses the diaphragm’s position to control the power to the electromagnet. Whenever the diaphragm is in its resting position or even farther from the electromagnet, a switch closes to deliver electric current to the electromagnet. The electromagnet then attracts the diaphragm’s center. But when the diaphragm moves closer to the electromagnet, as the result of this attraction, the switch opens and current stops flowing to the electromagnet. Because of this arrangement, the diaphragm moves in and out and turns the electromagnet off and on as it does. The diaphragm’s tone is determined by the natural resonances of its surface.

Why does microwave radiation affect plant seeds differently? If you microwave su…

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Why does microwave radiation affect plant seeds differently? If you microwave sunflower seeds 30 seconds, they germinate faster than if you did not microwave them at all, and yet if you microwave them for 60 seconds, the seeds do not germinate at all. If you do this same experiment with carrot seeds, the non-radiated seeds, the 30 second and 60 second seeds all germinate within 14 days. Why? Is it because the sunflower seeds are larger and absorb more radiation than the smaller carrot seeds? — ST, Mobile, AL

When you expose the seeds to microwave radiation, you are selectively heating portions of the insides of the seeds. Fats and oils don’t absorb microwaves well but water does, so the parts of the seeds that become hottest are those that contain the most water molecules. Evidently, heating the water-containing portion of a sunflower seeds slightly cause that seed to germinate faster, but heating that same portion too much sterilizes the seed. That observation indicates that a moderate temperature rise causes the chemical reactions of germination to occur more rapidly while a more severe temperature rise denatures some of the critical biological molecules and kills the seed. The absence of any effect in carrot seeds may indicate that they don’t have enough water in them to absorb the microwaves. It may also indicate that they can tolerate higher temperatures without undergoing the chemical reactions of germination and without experiencing damage to their critical molecules.

When you are looking at something and there is an object partially blocking your…

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When you are looking at something and there is an object partially blocking your view (e.g., a fence or a railing), why with one eye closed does the barrier block your vision but with both eyes open you seem to look through the barrier? — DS

Your brain merges the images it obtains from your two eyes so that you “see” a composite image that is essentially a sum of what both eyes see. When you close one eye so that only the other eye is providing an image to your brain, any object that blocks your view chops a piece out of the distant scene. No light from that portion of the scene reaches your open eye, so you can’t see that portion of the scene. But when you have both eyes open, the image observed by one eye can compensate for any missing pieces in the image observed by the other eye. Since the barrier you are looking through chops out a different piece of the distant scene for each of your two eyes, the composite image that your brain assembles from these two individual images will include the whole scene.

When you talk about the magnetic tape and recording, is it the pressure or frequ…

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When you talk about the magnetic tape and recording, is it the pressure or frequency that is being recorded? Are pressure and frequency interrelated?

Sound consists of pressure fluctuations. The stronger those pressure fluctuations, the louder the sound. The rapidity with which the air goes between a pressure increase and a pressure decreases determines the frequency of the sound and the pitch that we hear. So the extent of the pressure fluctuations, their amplitude, determines the sound volume while the number of pressure fluctuations each second, their frequency, determines the sound pitch. The tape recorder detects both and records both. The louder the sound, the deeper the recorder magnetizes the tape. The higher the frequency of the sound, the more often the tape recorder reverses the magnetization of the tape’s surface.

How long will a magnetic tape stay magnetized? Won’t it lose its magnetization v…

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How long will a magnetic tape stay magnetized? Won’t it lose its magnetization very fast, like we saw with the iron nails?

At room temperature, a magnetic tape will remain magnetized for years and years. It is made of much harder magnetic materials than the nails are made of and it is much harder to demagnetize than the nails. In effect, it is covered with tiny permanent magnets and you have seen permanent magnets that remain magnetic for decades or centuries.