Big Think

How often can an X-ray be taken? Radiation is dangerous in principle. And it is desirable that the dose during examinations does not exceed the amount corresponding to the background radiation. According to Russian regulations, this is no more than 1 millisievert (mSv) per year. A patient receives 0.08-0.11 mSv during one examination. The dose on digital units is 0.04-0.05 mSv. This means you could be examined 10-20 times a year. But if treatment requires constant X-ray monitoring, the norms are increased, because refusal of monitoring poses a greater risk to the patient than additional doses of radiation.

How does time pass in space? Time flows differently in space and on Earth. According to scientists, it is because of gravity. The stronger it is, the slower time will go. For example, on the ISS, which orbits the Earth in a low orbit, time flows a fraction of a second faster than on the planet. Satellites in high geostationary orbits run even faster. We don't feel the change in the passage of time on the station. Because we do not fly at high altitudes and not so far from the Earth, only 400-420 kilometers. And, of course, if these changes exist for some milliseconds, we will never sense them.

Is it true that batteries wear out from a full charge? They do, especially if you store them that way. Lithium battery wear is due to the fact that not all of the lithium ions that carry a charge to the anode are returned to the cathode during the charging process. Some of them remain in the electrolyte, reducing the capacity of the battery. Most of the life is wasted by overdischarging and partly by overcharging the battery, especially if the battery is stored charged. In modern gadgets, the limits of discharge and charge are set so that the resource is enough for about 400-500 full cycles. If the battery is not set to 0% and 100%, it will endure more cycles.

How is sound extracted from vinyl records and music played? Sound is extracted from a vinyl record by means of the needles of machines specially designed for this purpose - first gramophones, then electrophones or electric record players. As the needle moves along the grooves of the record's track, it begins to vibrate. This vibration, in turn, produces an electrical signal identical to the one picked up by the microphone in the recording studio. In modern audio devices, this signal passes through a phono stage, an amplifier, and becomes audible through the speakers.

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What is the reason why runners start from a low start? Before 1887, all runners stood at the start at full height, waiting for the command to start running. The low start was invented by Sherrill, an American sprinter, after observing kangaroos ducking to the ground before starting. When he used the new method despite the protest of the judge and the mockery of spectators, he immediately won the race. So, don't be afraid to do something new, even if others don't like it!

Are there any materials that reflect X-rays? Most materials reflect such beams poorly, because energetic X-rays interact weakly with matter, penetrate deeply, and are absorbed. However, mirrors can be made from dozens or hundreds of alternating nanometer-thick coatings. Together, these layers reflect a few percent of soft X-rays. For harsher radiation, sliding-drop mirrors are used. Falling at an angle of about 1° onto the polished surface of a heavy metal (gold, platinum, iridium), X-ray quanta are reflected like ordinary light. X-ray telescopes with such mirrors are on the XMM-Newton and Swift orbiting observatories.

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Why can't you pull the pin out of a grenade with your teeth, like in the movies? The fact is that the grenade is a dangerous weapon that, when detonated, has a large kill radius. To prevent it from going off accidentally, the pin mechanism is made very tight. You can't just pull it out like that. Even if you can do it with your teeth, the "hero" will then eat only porridge and ground fruit - he will not be able to chew.

Can a shark feel a drop of blood in the water? Some movies, such as Jaws, have cemented in our minds the notion that sharks can sense a drop of blood from miles away and almost instantly get close to their prey. Sharks do develop this sense, but not as much as we used to think. Some researchers agree that a shark can sense blood in the volume of water equal to that of an Olympic swimming pool. So if you cut yourself in the water and are sure there is no shark within fifty meters, you can rest easy. If you're not sure, you'd better get out of here.