staccato signals of constant information
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I confess that I was not impress by Obama campaign, words like "Change", "Hope", "Yes we can" seem too much abstract and vague.
However I now admire his courage to say the thing we can listen in the video linked bellow. Just remember that he is a chosen candidate to the USA presidency. Where radical Christians are said to make and unmake presidents.
To see the video just click:
http://www.youtube.com/watch?v=_IHQr4Cdx88
Lot of videos (of shows) here:
http://youtube.com/results?search_query=george+carlin&search_type=&aq=f
The Earth (and the Moon) as "seen" from Mars - picture taken on October 3, 2007, by the HiRISE camera on NASA's Mars Reconnaissance Orbiter. 
Physics for future-biologists or future-physicians who what to learn the least possible of physics, but still menage to finish university.
This text is free for everybody to use under the “Attribution + ShareAlike” Creative Commons license.
See http://lasers-in-the-jungle.blogspot.com/2008/06/attribution-sharealike.html
Part 3
Q) What is the plural of nucleus?
A) Nuclei.
Q) What is “nuclear fission”?
A) The splitting of the nuclei of atoms into two fragments. Each of the resultant parts has a low mass number and the results are of approximately equal mass (mass number).
Q) What are the principal uses for “nuclear fission”?
A) The nuclear fission of heavy elements, i.e., elements with high atomic number (usually uranium or plutonium) is accompanied by conversion of part of the mass into energy. That is the principle in which is based the nuclear reactors and the atomic bomb (A-bomb).
Q) Are “nuclear fission” and “nuclear splitting” the same thing.
A) Almost. The correct wording is “nuclear fission”, although we could use “nuclear splitting” in colloquial language. However it is correct to use spit when we need a verb. So we would say: in nuclear fission we split (verb) the atom.
Q) Can all elements be subjected to fission?
A) Theoretically yes (except element n.1, hydrogen) but only the fission of elements with atomic number greater then 26 can produce energy (the element with atomic number equal to 26 is called iron). However, on earth, we only use uranium (element n. 92) or plutonium (element n. 94 – yes is a transuranium element, an artificial element).
Q) What are nuclear reactors used for?
A) Usually to produce energy. But also to create various radioisotopes, such as americium-241 for use in smoke detectors, and cobalt-60, molybdenum-99 and others, used for imaging and medical treatment, has we have seen before. Some nuclear reactors based in uranium also produce large amounts of plutonium.
Q) Are nuclear reactors the only way to produce radioisotopes?
A) No, they can also be made using accelerators (particle accelerators).
Q) What is “nuclear fusion”?
A) It is the fusion of atomic nuclei into a nucleus with heavier mass number element. Just the opposite of nuclear fission (verb: fuse fused fused)
Q) What are the principal uses for “nuclear fusion”?
A) The nuclear fusion of light elements, i.e., elements with low mass number (usually hidrogen-2 and/or hidrogen-3) is accompanied by conversion of part of the mass into energy.
The energy produced is enormous, but mankind has not yet learned how to use it as a source of usable energy. However the principle is used to build hydrogen bombs (H-bombs) that are usually much more powerful that A-bombs. (the exact mechanism of H-bombs is a well guarded secret).
Our Sun, at this moment, produces its energy fusing hydrogen into helium.
Q) Can all elements be subjected to fusion?
A) Theoretically yes but only the fusion of elements with atomic number less then 26 can produce energy (the element with atomic number equal to 26 is called iron). However on earth we only fuse hydrogen, and only by a very short period of time.
Q) What about element n. 26 (iron)? Can it be used on fission or fusion?
A) No. It is a special element on that regard. It can be split or fused, but no energy is produced in the process.
Q) What about the famous Einstein equation E=mc2?
A) It explains the conversion of mass to energy, both in fission and fusion.
Q) What is c2? (read: c-squared)
A) The square of the velocity of light in the vacuum.
Q) What is the velocity of light in the vacuum?
A) 300 000 000 m/s
Q) That is the visible light?
A) Not only. Every form of light, visible or not visible, propagates in the vacuum at the same velocity.
Q) What is a telescope?
A) Is an instrument composed, mainly, of lenses and/or mirrors, that allows people to see distant objects, that could not be seen with a naked eye.
Q) How important was the telescope for the start of “modern science” in XVI and XVII centuries?
Q) Our knowledge of the universe had remained quit constant (and WRONG) since the Greek civilization. The possibility open by the use of the telescope by Galileo, allowed us a much more detailed view of stars and planets, and was the fundament of changing our view of the solar system from a geocentric view (with earth at the center), held by ancient Greek and Chinese astronomers, to a heliocentric view (with the sun at the center) which is the modern concept.
Q) Can you explain in more detailed the construction of the telescope?
A) No. There are hundreds of different types of telescope using different types of lenses and different types of mirrors assembled in diverse ways. Explaining all that will take ages.
Q) Do the telescopes work only with visible light?
A) When we speak about telescopes we are using speaking of optical telescopes, which work with visible light. However there have been built telescopes that work with radio waves (radio telescopes) as well as telescopes working with infrared, telescopes working with X-rays and telescope working with gamma rays. Those are non-optical telescopes and are build in a very different way, if compared with optical telescopes.
Q) What is a microscope?
A) The microscope is similar to a telescope but upside down. Usually only lenses are used (no mirrors). With a microscope we can see small things, not visible at naked eye.
Q) That is the optical microscope (visible light). Isn’t it?
A) Yes. We can also build infrared microscopes, ultraviolet microscopes and X-ray microscopes, which are more complex and we are not going into details.
Q) Other types of microscopes?
A) Yes. More common: “Electron microscopes” and “scanning probe microscopes”. They are the most powerful microscopes and they do NOT use any electromagnetic radiation.
Q) What is “electric current”?
A) Is a flux of electrons flowing through a conductor (conductor: explained latter).
Q) That is “beta radiation”? Isn’t it?
A) No. “Beta radiation” and “electric current” are very different concepts. Although both are “stream of electrons” (yes. Physics is hard).
Q) So can you tell me the difference between “beta radiation” and “electric current”?
A) “Beta radiation” is generated by radioisotopes, fission reactors or particles accelerators. “Electric current” is usually generated by batteries or electrical generators (as used in power generation stations).
This is the same that saying that beta radiation comes from inside the nucleus (yes, I know that we do not have electrons inside the nucleus, however in certain conditions a neutron divides itself into an electron plus a proton...). Beta radiation is nuclear physics.
Electric current comes from disturbing the electrons that orbit the nucleus. That’s classical physics.
Also:
In “beta radiation” the electrons move very fast and are very energetic. Not so in “electric current”.
“Beta radiation” propagates very well in vacuum or in the air, not so well in solids. “Electric currents” do not propagate in vacuum, propagates very hardly in the air (lightning in a thunderstorm) and propagates very well in solids called conductors.
Q) What is, finally, a conductor?
A) Usually conductor is the same of “good conductor” and the opposite of “bad conductor” A conductor is an element or alloy or mixture can that easily conduct “electric current”. A “bad conductor” is usually called an isolator.
Q) Can you give me example of conductors (good conductors)?
A) Yes. Usually metals are good conductors (very used conductors: cooper, iron). But also graphite, which is not a metal, is a very useful conductor.
Q) Is water a good conductor?
A) Pure water is a very BAD conductor. However with something dissolved it can became a good conductor.
Q) What is a superconductor?
A) It is a conductor that is a perfect conductor where the electric current circulates with absolutely no opposition.
Q) Is it easy to obtain a superconductor?
A) Is difficult because known superconductors only operate at very low temperatures. Finding superconductors at room temperature would be a revolution in human society.
Q) Are superconductors important in applied science?
A) Yes. Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) are based in superconductivity. Most accelerators are also based in superconductors.
Q) How do we obtain the (very low) temperatures to obtain superconductivity?
A) Using liquid helium
Q) Is easy to manipulate liquid helium?
A) No. Liquid helium is expensive and needs a careful manipulation. However modern equipment can maintain the helium inside with minimum maintenance. Sometimes a “refill” can be needed. Any unexpected escape of helium can be an hazard.
Q) What is a semiconductor?
A) That is the hardest question in this notes :-)
Semiconductors are an essential part of our lives today. Computers, cellular phones, MP3 players, modern radios and televisions, even part of the motors of recent cars are based on “chips” also called “integrated circuits”, “microchips” or “silicon chips”.
A chip is just a complex composition of a very large number of semiconductors (and other elements). Same chips have more then 100 000 000 (an hundred million) semiconductors.
Q) You have not answered my question. What is a semiconductor?
A) Is a material that can, depending of the circumstances, behave like a conductor, behave like an isolator, or behave as something in between. It can sometimes amplificate the (an) electric current.
Q) Which are the simplest devices composed of semiconductors.
A) The transistor and the diode.
Q) What is a transistor?
A) The simplest semiconductor device that can amplify an electric signal.
Q) What is a diode?
A) A device that conduces electricity in one direction but not in the other.
Q) What is “pressure”?
A) Pressure is the force, applied over a surface, divided by the area of that surface. The surface can be real or imaginary. The pressure is measured in pascal (abrev: Pa). a kPa is equal to 1000 Pa. And old unit of pressure is “millimeters of mercury” (Abrv: mmHg, Hg been the chemical symbol of the element “mercury”) another unit is “atmosphere”.
Q) Just one useful exercise, can you calculate the pressure in the base of a column of mercury, 120 mm high?
A) Sure. Let’s see.
Suppose the base is is 1 mm2 (I am writing mm2 as mm-square, because I have problems writing upper-indexes).
The volume is 120x1 = 120 mm3 = 0.120 cm3
The density of the mercury is 13.534 g/cm3 so the mass is 0.120x13.534 = 1.624 g=0.001624 Kg
So the weight (force) is equal to0.001624x 9.8 = 0.01590 N
[Remember p=mg, g=9.8 m/s2]
Pressure = force (weight) / surface
Pressure = 0.01590 N / 1 mm2 = 0.01590 N / 0.000001 m2 = 15900 Pa = 16.9 kPa
Q) What if the surface is NOT 1 mm2?
A) The result is the same. Just try.
Q) What is the other name of mercury?
A) Quick Silver. You should NOT use this name in science. It is an old designation.
Q) What is blood pressure?
A) Is the pressure inside the body, in the blood.
Q) Does the blood pressure vary inside the human body?
A) Yes. It varies with the type of vessels and also varies with the movements of the heart.
Q) How should we measure the blood pressure?
A) I read that we should measure it at an artery. We should identify a maximum and a minimum of the pressure. In the artery. However that should be learned with a specialist not with a physicist.
Q) What are the normal (healthy) human limits?
A) They are 120 mmHg (16 kPa) and 80 mmHg (11 kPa), I read someplace. This is usually called 120-80. The value is very variable with a lost of circumstances very very beyond physics, I just leave this as an example so you have a notion of the values involved.
Q) Which unity should I use to measure blood pressure?
A) That is your choice. Just do NOT mixed up. Probably mmHg is the most used, but perhaps kPa is the future. Now you know how to convert one into the other.
1 kPa = 7.5 mmHg
Q) What is thermodynamics?
A) Is the study of “heat” (thermo) in transit (dynamics).
Q) What is the most obvious “object” of study in thermodynamics?
A) The “internal combustion engine”.
The “internal combustion engine” burns something and gives us energy in the form of movement.
Q) What is an “internal combustion engine”?
A) The “thing” that takes fuel and make my car run.
Q) Can I use the “motor” instead of the word “engine”?
A) Yes, but that may sound a little strange for a native speaker.
The rules are quite confusing, so if you are referring to an “internal combustion engine” use always engine. However a “car” with an “engine” is a “motorcar”. Go figure.
Q) So thermodynamics only applies to engines?
A) No. Although (modern) thermodynamics started studying engines, today it managed to by applied to a lost of disciplines, namely “biology” and “medicine”.
Q) What are the bases of thermodynamics?
A) The five laws of thermodynamics and the concept of “potentials”, Entropy is also an important concept.
Q) What is the most know potential?
A) Enthalpy.
Q) What is “heat”?
A) The everyday life concept is mostly appropriate. Just remember that “heat” is just a form of energy and that “heat” and “temperature” have always different meanings.
Q) What is the difference between “heat” and “temperature”?
A) Just an example. If you have a campfire (outdoor fire) you can have a few people heating themselves around. If you have two similar campfires you double the heat (the double of the people can heat themselves) but the temperature is the same.
Q) Other example please
A) If you can comfortably heat a room with an electrical heater (radiator), you need two similar heaters to heat a biggest room to the same temperature. So the temperature is the same but you have needed the double of heat.
Q) What are the units for “heat” and “temperature”?
A) Heat is a form of energy, so it is measured in joule (abrev: J) as any energy. And old unity may still be in used, is the calorie. 1 calorie = 4.18 J. Calorie is only used in “heat” context.
Q) What is a “big calorie”?
A) 1000 (one thousand) calories.
Q) That is easy. Isn’t it?
A) No because some people abbreviate “big calorie” to “Calorie” (note the capital “C”). So “calorie” and “Calorie” are different things – a mess. Use joule instead.
Q) Could somebody mess up?
A) Do you remember coca-cola adds? Just 1 calorie? Wrong. Just 1 Calorie, 1000 times more.
Q) What about temperature?
A) Temperature is, most of the time, measured in “º” (read: degree) or “ºC” (read: degree-centigrade or degree-Celsius) or just “Celsius”. Aglo-Saxonics also use “degrees Fahrenheit”.
Q) What is absolute temperature?
A) Just add 273.15 to the temperature measured in ºC. The absolute temperature is measured in “º K” (read: degrees-Kelvin).
In physics, most of the times, we use ºK. It is an important conclusion of thermodynamics that we cannot have a temperature bellow 0 ºK (read: zero-degrees-Kelvin).
Physics for future-biologists or future-physicians who what to learn the least possible of physics, but still menage to finish university.
This text is free for everybody to use under the “Attribution + ShareAlike” Creative Commons license.
See http://lasers-in-the-jungle.blogspot.com/2008/06/attribution-sharealike.html
PART2 – Radiation (includes: sound, optical spectrum, radioisotopes)
Q) What is radiation?
A) Radiation is something that radiates.
Q) Can you give more details?
A) I can list the type of radiations we are going to describe here. Electromagnetic radiation, alpha radiation, beta radiation, sound radiation. We are not going to speak of another type of radiation (just an example: neutrino radiation).
Q) What about gamma radiation, x-ray radiation, ultraviolet radiation, light radiation, infrared radiation?
A) They all are forms of “electromagnetic radiation”. More about that soon.
Q) Alpha, beta, gamma. Are those Greek letters?
A) Yes, and you can use the Greek letters instead. But I do not have Greek letters in my keyboard, so I must write them as I am doing NOW.
Q) What is the other possible name for “electromagnetic radiation”?
A) Light! I agree that this is difficult to understand because we are used to think in “light” as something we associate with vision. But that is not always the case. We can see violet, but we cannot see ultraviolet. We can see red, but not infrared. Believe me there are a lot of other “types” of light we cannot see - but can be detected by our instruments or apparatus. We will call “visible light” to the type of electromagnetic radiation we can see with ours yes, and simply “light” to all kind of electromagnetic radiation.
Q) If there is a lot of “types” of light, was is the difference between then?
A) Frequency. To be more precisely range (or interval) of frequencies.
Q) I began to see, but can you systematize?
A) Here we go. A list of different type of light (or electromagnetic radiation), and their interval of frequencies:
Radio (TV, etc) from 3 Hz to 300 GHz
Infrared – from 300 GHz to 400 THz
Visible light - from 400 THz to 790 THz
Ultraviolet – from 790 THz to 30 PHz
X – rays – from 30 PHz to 30 EHz
Gamma rays – from 30 EHz to 300 EHz (or more)
(But nobody know those numbers by heart)
As you could imagine those divisions are a little arbitrary and, a lot of sub-divisions are possible and are use in specific fields of work or research. But here we would try to keep things as simple as possible. Just an example, microwave ovens work with a radiation near 2.5 GHz, in a band called “microwaves”, but for us, at the moment, is just radio.
Q) What is a “band” (in this context)?
A) That one is easy to understand. Is just a range or interval of frequencies.
Q) What happen below 3Hz?
A) Nothing really interesting or useful (as far as we know at the moment). So no specific name.
Q) What above 300 EHz?
A) We continue to call them gamma rays.
Q) I suppose visible light is an important subject. Can you give us more details?
A) Sure. Visible light is a band between 400 THz to 790 THz, but can be considered divided in smaller bands. Those bands are simply the “rainbow colors”, i.e., red, orange, yellow, green, blue, indigo, and violet (mnemonic: ROY G. BIV - or - "Richard Of York Gave Battle In Vain”).
Q) What does the word “optic” mean?
A) Although we rarely use that word alone, that mean something related to the visible light (the word has the same root of optician)
Q) What is an “optical spectrum”?
A) Just the “rainbow colors” set aside exactly the way they appear in rainbow. The rainbow itself is a good example of the optical spectrum.
Q) What is the plural o spectrum?
A) Spectra.
Q) The rainbow is an example of a spectrum. Are there other spectra?
A) The rainbow is the spectrum of the sun (white) light. Other sources can have different spectra. In physics sometimes we can know the composition of a source of light just studding carefully the spectrum of the light coming from it.
Q) Everybody can see those colors well?
A) Most normal people can see the colors, but usually indigo is quite difficult to differentiate from blue or violet (some people are better at that that others, but most people do not know if they themselves are sensitive to indigo).
Q) What is “color blindness”?
A) Is the inability to perceive differences between some (or all) of the colors that other people can see.
There are some different types (forms) of “color blindness”. In the most severe form people cannot differentiate any color. Some times people can differentiate some (but not all) colors
The word “Daltonim” is also used, but it's mean is no exactly the same, so it's meaning should only be used in a more detailed context. “Color blindness” is, or can be considered, a disability. Problems with “indigo”, as described above, are not considered “color blindness”.
Q) You mean a color blind cannot see one (or more colors)?
A) No. He or she can see, but cannot DIFFERENTIATE the colors although they see them. It's like looking at a black-and-white picture. You can see everybody in the picture but it is impossible to know if a person is using it's red or blue dress.
Q) We are speaking about human, what about other animals.
A) We, as human have a quite good color vision. Some other animals could be considered “color blind” if comparer with humans.
Some animals can see frequencies we cannot see. Some insects can see the radiation just above violet (in a range called ultraviolet). Some reptiles can sense infrared (frequencies just below red) – but not using their eyes.
All in all most animals can see only the colors we see, with small differences. To be all to differentiate them all is a different thing. Some other animals have, however, better color vision then we do (some birds, fishes, etc).
Q) But there are some colors mission from the “rainbow colors”. Like pink, purple, magenta, brown. Why?
A) They are combination of different “rainbow” colors.
Q) What is “white”?
A) The mixture of all rainbow colors in the same proportions seen in the rainbow.
Q) What is “black”?
A) The absence (nonexistence) of ANY rainbow colors (or others colors).
Q) I would like to see the rainbow colors, but I do not have the time to wait for a rainbow.
A) In most laboratories you can find a not expensive apparatus called a “prism”. If you see some light to one of its faces you can probably see the rainbow colors from other face (some try and error could be necessary to find the right positions). Just remember to use a white source of light (sunlight is OK).
Q) What is “intensity”?
A) Is the scientifically correct word for what we can call, in colloquial speech, "amplitude", "strength" or "level".
Using an example with visual light is easier. Now I have a 50 W light bulb over my desk. It's OK. But if I change to a 100 W light bulb I double the intensity of the light in my desk.
The correct definition is “energy divided by time (duration), divided by surface”.
Q) What does mean “wave”, “ray(s)”, in this context.
A) Without going into more details, means the same thing as radiation.
Q) What is the effect of electromagnetic radiation in the human body?
A) We will see that is more details, but it depends of the “type” of radiation, the intensity and the duration of the exposition as is easy to understand. As a rule all radiation is harmful. Also, as a rule, the greater the frequency the more the damaging, but this is just a rule, that does not work all time.
There is a lot of research (an controversy) about radio waves. The radio frequencies used by cellular phones, and wireless computer networks, are not very far from frequencies use by microwaves ovens. So, in a sense, each time we use our cellular we “microwave” (like in “microwave oven”) our brain. HOWEVER most specialists will tell you that the intensity of the radiation is too small to cause you any harm. I keep the use of my phone as short as possible. It is less expensive this way.
Q) So radiation is always dangerous?
A) Yes, but sometimes the destruction can be useful if you destroy unwanted tissue (s). Also sometimes radiation is used in a resourceful way.
For example (we would see more soon) x rays are dangerous, but very useful to take “pictures” of the inside of your body. Since one received only a few seconds of exposition every year (or something around that) we are not at danger, and x-rays are very useful for diagnostic (however someone operating the machine day after day requires some appropriate protection, usually in the form of distance from the machine, special vestiary, protective walls, etc).
Sun light (visible light, plus some infrared and ultraviolet), if used in a controlled way is healthy.
Q) What are “photons”?
A) We sometimes describe the electromagnetic radiation (also known as light) as a stream of particles called photons (same root as photography). We will not explore a lot that concept here.
Q) What time of radiations has not been explained yet?
A) Sound, alpha radiation and beta radiation - are NON-electromagnetic radiation.
Q) What is sound?
A) Well, almost everybody knows the meaning of sound and the common perception is right. In the physical context sound can be considered to be changes in pressure (more on pressure, late).
Q) We have “frequencies” in sound?
A) Yes.
Q) Can we ear all frequencies?
A) No. The human audio range is between 20 Hz and 20KHz, but that’s a very good audition. Some people can listen only between 70 Hz and 13 KHz. Also with age same lost of audition is usual.
Q) Can you explain the change of sensibility with age?
A) Some young people use high pitched (high frequency) tone ring in their phones, so adults cannot ear and are not aware of what is going on. Some old people use high-pitched sound, with high intensity, to “repel” young ones.
Q) How do we sense “frequency” related to sound.
A) As pitch (in colloquial terms: highness or lowness of sound). For example, in a piano, when we strike different keys, we get different frequencies. On the left we got low frequencies (low sound, low pitch). On the right we get high frequencies (high sound, high pitch).
Q) And what about other animals?
A) That changes a lot. Just two examples. Dogs can ear above 25 MHz, sometime to 45 MHz. A dog whistle works around 25 MHz, so dogs can hear, but people cannot. Bats can ear frequencies as high as 80 KHz, or even more, but they use the sound for the purpose of locating things around, like sonar, used by boats to locate fish.
Q) What is the beta radiation?
A) Just a flux of electrons at high velocity (we exclude were a more exotic form of beta radiation, which include an exotic particle called positron, just forget).
Q) What is alpha radiation?
A) Just a flux of alpha particles
Q) OK, but what is an alpha particle?
A) It's a particle that consists as two neutrons plus two protons. It sure looks like the nucleus of element n. 2 (which, by the way, is called helium).
Q) What is a radioisotope (also known as radionuclide)?
A) Any isotope that radiate some kind of radiation
Q) What kind of radiation radiates a radioisotope?
A) (Sounds funny) A radioisotope can radiate radiation alpha beta and/or gamma (other “things” can be radiate, but we are not going to talk about that).
Q) What is radioactive decay?
A) The process a radioisotope goes through when it radiates.
Q) What is the importance of radioisotopes?
A) There are a lot of radioisotopes (some natural, most artificial). Choosing the right isotopes we can usually get the kind of radiation we need for a specific task. The radioisotopes are just the way the nuclear industry arrives to the laboratory, to medicine and to the industry – and to the home.
Q) Do people have radioisotopes at home?
A) Probably – If they have a fire/smoke detector. Most of the times radioisotopes should be handle with extreme care, always using a protocol for the given source.
Q) Are gamma rays dangerous?
A) Gamma rays are usually the most destructive radiation. It can “burn” the tissues, but also alter the DNA of the cells, which eventually leads to cancer and other anomalies.
Q) Are gamma rays useful?
A) Yes. They have a lot of useful applications. It can be used to sterilize medical equipment. It can be used to kill bacteria in the food, preventing that stuff to go bad in a short period of time (however consumers have some kind of reserve about eating irradiated food – if they have the choice)
Also we can use gamma radiation to destroy cancer tissues, or other kind of tissue harmful to the patient. The main problem is to keep other tissues from the gamma rays. Usually the source is cobalt-60, an artificial radioisotope of cobalt (element n.27).
Gamma rays are hard to shield. We need 1 cm of lead or 5 cm of concrete, just to reduce to 50% the intensity of a beam.
Also people can receive the radioisotope technetium-99, which irradiates gamma rays. While the technetium circulates through the body if, it radiates gamma rays, that are recorded, from outside, with a camera that records gamma rays. This allows a diagnostic of many problems in the patient.
Q) Are x-rays dangerous?
A) Yes. The some kind of danger of the gamma rays, but they are not so damaging.
Q) Are x-rays produced by radioisotopes?
A) No. Radioisotopes do not generated X-rays. X-rays are created within a sort of light bulb, but very different inside (and much more complex) that a normal light bulb.
Q) Is beta radiation armful?
A) Yes, it can do the same of gamma rays.
Q) Is beta radiation useful?
A) Yes. It is not very different from gamma. The source of beta radiation is usually the Strontium-90.
Q) Is alpha radiation armful?
A) Most of the time is not, because it is not very penetrating, and does not penetrate the skin. However if someone managed to swallow a source of alpha radiation, that can be very damaging because the alpha particle is shouted to cells at very short distance.
Q) But is easy to swallow an alpha source?
A) The smoke detectors in the houses have a radioisotope, americium-241, that irradiates alpha. Manipulation the americium is not dangerous because the skin protects us from the rays. However it would be very damaging if we ingest the alpha source.
Q) Is alpha radiation useful in medicine?
A) Not really.
Q) Any other way to produce radiation?
A) Particle accelerators. They have been used more and more on medicine. X-rays produced by accelerators have been replacing gamma-ray treatments (that, see above, use usually a cobalt-60 radioisotope as source). The radiation is more precisely delivered and the source is more reliable.
However accelerators are big.
Q) Does the human body radiate visible light.
A) It does not. That is why we cannot see ourselves in the dark.
Q) Does the human body radiate any radiation?
A) Yes. It, the human body, as any hot-blooded animal radiates in the infrared. Although we cannot see it, some cameras record it and translate the different frequencies of infrared to the visible range (which is called false color). Recently they have used this kind of cameras to fast detection of people with flu (with temperature above normal) in some airports.
Physics for future-biologists or future-physicians who what to learn the least possible of physics, but still menage to finish university.
This text is free for everybody to use under the “Attribution + ShareAlike” Creative Commons license.
See http://lasers-in-the-jungle.blogspot.com/2008/06/attribution-sharealike.html
Part1 - INTRODUCTION
Introduction 1 – modern physics
Q) What is “modern physics”
A) It's the physics developed in the XX and XXI centuries
Q) What are the highlights of modern physics
A) “quantum mechanics” and “relativity”
Q) quantum mechanics and relativity are easy subjects?
A) No, they are difficult. They are usually only taught at physics courses
Q) What else important brought us modern physics?
A) The modern concept of “atom” and its inside, i. e. “atomic physics” (or “atom physics”) and “nuclear physics”.
Q) What the name of physics that is not modern physics?
A) Classical physics
Introduction 2 - frequency
Q) What is “frequency”?
A) The number of times a phenomenon repeats itself in a unity of time (usually in each second).
Q) What is an hertz (abbreviation: Hz)?
A) The most usual unity of frequency. If something repeats itself twice each second, we say that it has a 2Hz frequency. Three times a second = 3 Hz, and so on.
Q) Why Hz starts with a capital “H” and hertz does not?
A) Nothing really important there. Just the rules. Please take care that if you are speaking about somebody called Hertz, or about a car rental company called Hertz, you should always use a capital “H”. Once again that just the (grammar) rules.
Q) What is a EHz, PHz, THz, GHz, MHz, kHz ?
A) The letter before Hz is just a short way to write a lot of zeros. There is also a name (prefix) for each case. The prefix is use when we are not using the abbreviation of hertz.
E=18 zeros (prefix: Eta)
P=15 zeros (prefix: Peta)
T=12 zeros (prefix: Tera)
G=9 zeros (prefix: Giga)
M=6 zeros (prefix: Mega) [aka million]
k=3 zeros (prefix: kilo)
so, for example,
1 EHz = 1 000 000 000 000 000 000 Hz = 1 Etahertz
1 MHz= 1 000 000 Hz = 1 Megahertz = 1 million hertz
1 kHz = 1 000 Hz = 1 kilohertz
Q) What is a million
A) 1 000 000. So one million hertz = 1 000 000 Hz = 1 MHz
Q) What is a billion?
A) Run away from that word as hell. In Europe nobody ever agrees with the meaning of a billion.
In the USA a billion is a thousand millions, i. e., 1 000 000 000.
In Europe some (most?) people claim 1 billion is a million of millions, i. e. 1 000 000 000 000.
Introduction 3 – The atom
Q) What are the atoms made of?
A) Electrons, protons and neutrons. Electrons have a negative ( - ) electric charge, protons neutrons have no charge and protons have a positive ( + ) electric charge. Electrons, protons and neutrons are often called “particles” in this context.
Q) How are electrons, protons and neutrons arranged inside an atom?
A) The protons and the neutrons are inside the central part of the atom (the nucleus). They do not move a lot. The electrons circulate around (OUTSIDE) the nucleus in complex orbits.
Q) That is all?
A) No :-). But understanding the true inside of the atom is only possible if you know your quantum mechanics and relativity which is too complex to use were. So let us stick with the simple model describe above. It has to make do.
Q) How many electrons, protons and neutrons, are there inside an atom?
A) Different atoms have different numbers. We have atoms with zero neutrons, but it has to have at least one proton, to be an atom.
Q) And how many neutrons?
A) Usually the number of neutrons is equal to the number protons, so the electric charge of each pair compensates exactly and the atom as an all do not have an electric charge. However the atom can lose one (or more) of its electrons and became positively charged or can gain and extra electron (or more) and became negatively charged.
Q) What is an ion?
A) Is a atom electrically charged as described above.
Q) What is the simplest possible atom?
A) An atom with only one proton in the nucleus and one only electron around it. It's called Hydrogen. It can even lose its only electron and became a positive ion of Hydrogen (with only one proton).
Q) How much do those particle ( electrons, protons and neutrons) weight?
A) The exact amount is not very important now. Just remember that a proton weight the same as a neutron and a electron weight much, much less. In physics we rather speak about the mass of the particles in the atom, but the concept is similar, the masses of the neutron and a proton are similar, and the mass of the electron is much lower.
Q) What is the mass number of an atom?
A) The mass number (A), also called atomic mass number or nucleon number (nucleon is a collective name for neutrons and protons) , is the number of protons and neutrons in an atom.
Q) What is the atomic number?
A) The atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom. It is traditionally represented by the symbol Z.
Q) What is greater, the mass number or the atomic number?
A) The mass number is always greater then or equal to the atomic number, as everybody could figure out, reading carefully the previous lines.
Q) What is an element?
A) Is a chemical substance that can not be found to be composed of other substances. Examples of elements are: hydrogen, carbon, nitrogen, oxygen, iron, gold, helium, uranium, etc.
Q) Is water an element?
A) No because it has been found that is composed of two substances, oxygen (abbreviation: O) and hydrogen (abbrev: H). Remember high school “water = H2O”.
Q) So water is a mixture of oxygen and hydrogen.
A) NO. Water is a compound of oxygen and hydrogen. The difference between mixture and compound is very important, but we would not talk more about that here. That is stuff for chemistry.
Q) At the atomic level, what defines an element?
A) The atomic number. The atomic number can even be use instead of the name of the element. For example the element “carbon” has 6 protons. So it can be called “element 6”, instead of carbon.
Q) Does the mass number describe an element?
A) No. If two atoms have the same atomic number, but different mass numbers it can be considered atoms of the same element, although different atoms.
Q) Confusing. Can you give me an example?
A) Sure. Let´s go back to the hydrogen. The must common form of hydrogen atom is composed of a proton an an electron and it is called hydrogen-1 (it is also called protium, or “light hydrogen”, but forget that, nobody uses that names any more). However it can be found hydrogen in other type of atom, with one extra neutron. That is called hydrogen-2 (also called “deuterium”, or “heavy hydrogen”). Other form of hydrogen is the hydrogen-3 (also called “tritium” or “triton”), with two extra neutrons (i. e. with one proton, two neutrons, in the nucleus).
Q) So, what is meaning of the number in hydrogen-1, hydrogen-2, hydrogen-3 ?
A) The number is the mass number, i. e. , the number of protons + the number of neutrons.
Q) Is there a common name for hydrogen-1, hydrogen-2, hydrogen-3 ?
A) Yes. They are called hydrogen isotopes.
Q) So what is an isotope?
A) Is one the the possible atoms types of a substance. For example, the element hydrogen, can have 3 different type of atoms, hydrogen-1, hydrogen-2, hydrogen-3, all of them can be called hydrogen and are referred as hydrogen isotopes.
Q) So hydrogen-2 is the “element number 2”?. Isn't it?
A) God's gracious NO! Read again the above text! The TWO as in “element n. 2” refers to the element with two protons in the nucleus (which, by the way, is called helium). The hydrogen has always 1 proton in the nucleus, so it is “element n. 1”. However the number of neutrons in hydrogen can vary, been zero in hydrogen-1, one in hydrogen-2 and two in hydrogen-3.
Q) What are the first and last elements?
A) The first element, obviously, in the element hydrogen, which is element n. 1. The last NATURAL element is element n. 92, called uranium.
However men managed to build elements with a mass atomic number greater then 92. Those elements are, of course, artificial, and are also called transuranium elements ( or transuranic elements) since they are “after” the uranium.
The last transuranium element, as far as I know, is the “element n. 122” called “unbibium” (symbol: Ubb) but that is not important because they may as well “build” an atom of “element. n. 123” today.
When I first study this “things” the last transuranium element was “element. n. 104”, called today rutherfordium (but this is not important, just one more example).
Q) Are isotopes common?
A) No. Usually one isotope for each element is common, all other are rare. For example in the oceans of Earth, approximately, if we have 6500 of hydrogen-1 we have 1 atom of hydrogen-2. Hydrogen-3 is even more, much more, rare.
Q) Can we have artificial (men made) isotopes?
A) Yes. Sometimes it is possible to build artificial isotopes even of natural (not man made) elements.
Q) Can you give me an example.
A) My pleasure. Cobalt. Cobalt is the element n. 27, meaning every cobalt atom has 27 protons. Natural cobalt has only one isotope, named cobalt-59 ( an element with only one isotope is called a monoisotopic element, as you could imagine).
However men can create cobalt-60, an artificial isotope of natural cobalt-59. Cobalt-60 is used a lot in medicine and biology, for several purposes (more on that later).
Q) So what's inside a cobalt-60 nucleus.
A) If you have read the previous text you know by now that inside a cobalt-60 nucleus we have 27 protons and 33 neutrons. (27+33=60).
Q) There are not much about electrons in the previous text, isn't it?
A) Yes. Electrons in not very important in what we said, that why this kind of physics is call atomic or NUCLEAR physics (nuclear, from nucleus = no electrons, only protons and neutrons).
However electrons are important in other fields of physics, for example in electricity that belongs to classical physics, not to modern physics (electricity and electron are words of common origin).
Q) What is a nuclide?
a) Is a type of nucleus. The concept is not very different from isotope, since isotopes have different kind of nucleus. We will not use the word “nuclide” a lot in this notes, but someone may like to know (or ask).
Q) What is the atomic mass?
A) Too complex to explain here. Not very different from mass number.
Q) What is the atomic weight?
A) Again: Too complex to explain here. Not very different from mass number (or atomic mass).
Q) I saw a symbol of an element with superscript or subscript (indexes). What do they mean?
A) Although we have always use correct ways to write our text, that is another way to write mass numbers and atomic numbers with superscript or subscript (indexes). The superscript give us the mass number and the subscript give us the atomic number. That is not easy to write superscripts or subscripts in a computer, so I am not using that.
Q) Where can I find a table with the number of electrons/protons/neutrons, mass numbers, atomic numbers, atomic masses atomic weights of each known element.
A) Go to you next library or bookshop and ask for a “periodical table of elements”. We would start from there.
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