Physics for future-biologists or future-physicians - Part 1

Physics for future-biologists or future-physicians who what to learn the least possible of physics, but still menage to finish university.

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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.