Author: Lou Bloomfield

Why is a satellite dish necessary to receive satellite broadcasts? Why doesn’t a…

Lou Bloomfield Leave a comment

Why is a satellite dish necessary to receive satellite broadcasts? Why doesn’t a conventional radio antenna work? — AW, Karachi, Pakistan

Normal television broadcasts use electromagnetic waves with relatively low frequencies and long wavelengths while satellite broadcasts use waves with relatively high frequencies and short wavelengths. The short wavelength waves from a satellite are known as microwaves while the longer wavelength waves from a normal broadcast station are generally known as radio waves. Since the optimal antenna size for receiving a particular electromagnetic wave is proportional to the wavelength of the wave, you need a smaller antenna to receive the microwaves from a satellite than you do the radio waves from a normal television station. However, the microwaves from a satellite are much weaker than the radio waves from a nearby television station and a small microwave antenna isn’t likely to absorb enough of them to produce a useable signal.

The solution to this dilemma is to concentrate the microwaves from a satellite with the help of an optical imaging system. Although it may not look like one, a satellite dish is really a carefully shaped mirror telescope. Just as the curved mirror of the Hubble space telescope can bring light from a distant star to a focus on an optical image sensor, so the curved wire mesh of a satellite dish can bring microwaves from a distant satellite to focus on a small microwave antenna. This microwave antenna sits at the focus of the satellite dish and absorbs the microwaves that the dish collects. The dish’s imaging behavior also ensures that microwaves from only one satellite are brought to a focus on the microwave antenna. You must redirect the dish or move the antenna in order to switch from one satellite to another.

What is gravity? We know Newton’s formula but he did not answer what the true na…

Lou Bloomfield Leave a comment

What is gravity? We know Newton’s formula but he did not answer what the true nature of gravity is. I hear talk about “gravitons” — is this real or just another elegant metaphor? — BC

Newton’s gravity has been superceded by Einstein’s gravity; the gravity of general relativity. In this understanding of gravity, the accelerations associated with gravity result from a curvature of space/time around concentrations of mass & energy. The gravity of general relativity is responsible for such exotic effects as the bending of light by gravity and the existence of black holes.

But physicists are still not satisfied with the gravity of general relativity. General relativity is what’s known as a “classical” theory of interactions—it does not include quantum physics and is thus considered to be incomplete. All the other classical theories of interactions have given way to quantum theories. For example, the classical theory of electromagnetic interactions, dating from the works of Oersted, Ampere, Maxwell and others in the 1800’s, was replaced in the 1940’s and 50’s by quantum electrodynamics, through the works of Feynman, Schwinger, Tomonaga, and others. Each time that a classical theory is replaced by a quantum theory, the responsibility for the interactions themselves shifts from classical fields (e.g., the electric and magnetic fields) to quantized or particulate fields (e.g., photons). These sorts of quantum field theories, theories in which interactions between particles are mediated by the exchanges of other particles (the particles of the quantized fields) are the bases for all modern interaction theories except gravity itself. People are still trying to quantize gravity but so far without real success. The particles that mediate gravitational interactions have been named gravitons, but the full theory in which these particles operate is still uncertain.

I have experimented with passing high voltage arcs through ionic compounds and h…

Lou Bloomfield Leave a comment

I have experimented with passing high voltage arcs through ionic compounds and have observed different colors when I do. An arc through salt (sodium chloride) produces a brilliant yellow light. How does this work? — JB, Lantana, FL

When electric current passes through air as an arc, the air becomes hot enough to vaporize the compounds you expose to it. As a result, there are individual sodium and chlorine atoms moving about in the arc itself. Like all atoms, a sodium atom resembles a tiny planetary system. It has 11 negatively charged electrons orbiting a massive, positively charged nucleus. But unlike our experience with the solar system, the electrons in a sodium atom can only travel in certain allowed orbits or “orbitals.” These electrons are normally found in the orbitals with the lowest possible energy. But when charged particles in the arc collide with sodium atoms, they often shift electrons in those atoms to orbitals with more energy. The electrons quickly return to their original orbits and emit their excess energies as light during their returns. In the case of sodium, the final step of the most common return path results in the emission of yellow light with a wavelength of about 590 nanometers. This yellow light is the same one you see in the sodium vapor lamps that are used to light highways and parking lots.

While sodium tends to emit yellow light, other atoms have different orbital structures and emit their own characteristic colors. Copper and barium atoms emit blue/green light while strontium atoms emit red light. These colored lights are the same ones that you see in fireworks.

What happens when a speaker blows?

Lou Bloomfield Leave a comment

What happens when a speaker blows?

A speaker produces sound by using magnetic forces to push or pull a thin surface—the speaker cone—toward or away from the listener. As the cone moves forward, it compresses the air in front of it and as the cone moves backward, it rarefies the air in front of it. These compressions and rarefactions are what produce sound. But if you try to drive the cone into motions that are too extreme by turning up the volume of an amplifier too high, the cone will reach the limits of its motion. At that point, the cone may tear away from the electromagnetic coil that pushes it back and forth or it may tear away from the supports at its outer edge. The electromagnetic coil may also burn up because of overheating. All of these failures are lumped together as “blowing a speaker.”

How does a car horn work?

Lou Bloomfield Leave a comment

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.

How can you run a clock off of a potato?

Lou Bloomfield Leave a comment

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.

Why does regular water freeze faster than salt water?

Lou Bloomfield Leave a comment

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.

I heard recently of someone with a pacemaker who went near a microwave oven and …

Lou Bloomfield Leave a comment

I heard recently of someone with a pacemaker who went near a microwave oven and his pacemaker faulted, with him needing urgent medical attention. How did this happen? I also know of someone currently undergoing chemotherapy, who was told by his doctor not to eat food from a microwave oven. Why?

A pacemaker contains electronic circuits and wires that can act as antennas for microwaves. If a pacemaker is exposed to sufficiently intense microwaves, currents will begin to flow in those wires and circuits, and these currents may cause computational errors to occur or they may cause the circuitry to overheat. But while a pacemaker is far more sensitive to microwave radiation than say your hand is, I’m still surprised that enough microwave radiation leaked out of the oven to cause trouble. I’d suspect a real problem with that oven.

As for the chemotherapy question, I can’t think of any reason why the doctor would suggest avoiding cooking food in a microwave oven. Unless I hear otherwise, I would suspect ignorance on the part of the doctor. The doctor may not understand the difference between “microwave radiation” and “gamma radiation”.

What is a Zobel network in an audio amplifier and how does it work? Is it an eff…

Lou Bloomfield Leave a comment

What is a Zobel network in an audio amplifier and how does it work? Is it an effective device or not? — CV, Cape Town, South Africa

My understanding is that a Zobel network consists of a resistor in series with a capacitor and that the capacitor is normally connected to ground. When you attach the free end of this network to a wire carrying an audio signal, the network acts like a frequency-dependent load. At very low frequencies, the capacitor has plenty of time to charge through the resistor and the network has little effect on the audio signal—it acts as though it weren’t there. At very high frequencies, the capacitor has no time to charge through the resistor and behaves like a wire. As a result, the network acts as though it were just the resistor connecting the audio signal wire to ground. So the impedance of the Zobel network varies from infinite at low frequencies to become equal to the resistance of the resistor at high frequencies. The crossover between these two behaviors is related to the RC time constant. I think that Zobel networks are used in audio amplifiers to dampen out high frequency oscillations that might occur in the absence of loads at high frequencies.

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

Lou Bloomfield Leave a comment

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.