AP Physics Period 2
In the spring of 1897 J.J. Thomson demonstrated that the beam of glowing
matter in a cathode-ray tube was not made of light waves, as "the almost
unanimous opinion of German physicists" held. Rather, cathode rays were
negatively charged particles boiling off the negative cathode and attracted to
the positive anode. These particles could be deflected by an electric field and
bent into curved paths by a magnetic field. They were much lighter than
hydrogen atoms and were identical "what ever the gas through which the discharge
passes" if gas was introduced into the tube. Since they were lighter than the
lightest known kind of matter and identical regardless of the kind of matter
they were born from, it followed that they must be some basic constituent part
of matter, and if they were a part, then there must be a whole. The real,
physical electron implied a real, physical atom: the particulate theory of
matter was therefore justified for the first time convincingly by physical
experiment. They sang success at the annual Cavendish dinner.
Armed with the electron, and knowing from other experiment that what was
left when electrons were stripped away from an atom was much more massive
remainder that was positively charged, Thomson went on in the next decade to
develop a model of the atom that came to be called the "plum pudding" model.
The Thomson atom, "a number of negatively electrified corpuscles enclosed in a
sphere of uniform positive electrification" like raisins in a pudding, was a
hybrid: particulate electrons and diffuse remainder. It served the useful
purpose of demonstrating mathematically that electrons could be arranged in a
stable configurations within an atom and that the mathematically stable
arrangements could account for the similarities and regularities among chemical
elements that the periodic table of the elements displays. It was becoming
clear that the electrons were responsible for chemical affinities between
elements, that chemistry was ultimately electrical.
Thomson just missed discovering X rays in 1884. He was not so unlucky
in legend as the Oxford physicist Frederick Smith, who found that photographic
plates kept near a cathode-ray tube were liable to be fogged and merely told his
assistant to move them to another place. Thomson noticed that glass tubing held
"at a distance of some feet from the discharge-tube" fluoresced just as the wall
of the tube itself did when bombarded with cathode rays, but he was too intent
on studying the rays themselves to purse the cause. Rontgen isolated the effect
by covering his cathode-ray tube with black paper. When a nearby screen of
florescent material still glowed he realized that whatever was causing the
screen to glow was passing through the paper and intervening with the air. If
he held his hand between the covered tube and the screen, his hand slightly
reduced the glow on the screen but in the dark shadow he could see his bones.
Rontgen's discovery intrigued other researchers beside J.J. Thomson and
Ernest Rutherford. The Frenchman Hernri Becquerel was a third-generation
physicist who, like his father and grandfather before him, occupied the chair of
physics at the Musee Historie in Pairs; like them also he was an expert on
phosphorescence and fluorescence. In his case, particular of uranium. He heard
a report of Rontgen's work at the weekly meeting of the Academie des Sciences on
January 20, 1896. He learned that the X rays emerged from the fluorescence
glass, which immediately suggested to him that he should test various
fluorescence materials to see if they also emitted X rays. He worked for ten
days without success, read an article on X rays in January 30 that encouraged
him to keep working and decided to try a uranium slat, uranyl potassium sulfate.
His first experiment succeeded-he found that the uranium salt emitted
radiation but misled him. He had sealed a photographic plate in black paper,
sprinkled a layer of uranium salt onto the paper and "exposed the whole thing to
the sun for several hours." When he developed the photographic plate "I saw the
silhouette of the phosphorescent substance in black on the negative." He
mistakenly thought sunlight activated the effect, ...
Mass is the amount of matter in an object. When you record mass the unit you use is grams. A medium sized leaf is about 1 gram, a potato chip 2 grams. A larger unit of mass is a kilogram. A kilogram is about the mass of a medium sized textbook. You need a balance to find mass. There are many kinds of balances. The gram is the unit used to measure m...
In a world where plants are at the bottom of the food-chain, some individual plant species have evolved ways to reverse the order we expect to find in nature. These insectivorous plants, as they are sometimes called, are the predators , rather than the passive prey. Adaptions such as odiferous lures and trapping mechanisms have made it possible f...
3. CISC Technology 4 3.1 Characteristics 4 3.2 The Advantages of CISC 5 3.3 The Disadvantages of CISC 5 4. RISC Technology 6 4.1 Characteristics 6 4.2 The Advantages of RISC 7 4.3 The Disadvantages of RISC 8 5. Conclusion 9 6. References 10 1.Abstract This report describes the CISC and RISC technologies. Describes the characteristics of...
have always been observed by people, many centuries before our time. People were always fond of clouds. They always wondered why some clouds were dark and others were white and fluffy, and why some clouds are so up high and others were so low that they looked reachable by the human hands. The most recent classification of clouds was accomplishe...
Hormonal Growth of Male Reproductive Function To complete this worksheet, select: Module: Continuity Activity: Animations Title: Hormonal Growth of Male Reproductive Function Introduction 1. What organs are involved in hormonal control of male reproductive functions? Testis, hypothalamus, an anterior pituitary. Hormonal Control...
Robert Wright is the science writer for Time Magazine. Because he writes for this popular magazine, he enjoys the attention of many readers who look to him to provide them with the latest news from the scientific community. After reading The Evolution of Despair, an article written by Wright, I came under the impression that he is both reporter a...
The atmosphere is divided into four layers based on their temperatures, the outermost region called the is located above the mesosphere and above this layer is outer space. The Greek name Thermos meaning "hot" shows that this is the hottest part of the atmosphere. Temperature here steadily increases with height, beginning at about 85 km (53 mi) a...
according to by Anna Selby is derived from the ancient practice of using natural plant essences to promote health and well-being. It consists of the use of pure essential oils obtained from a wide assortment of plants, which have been steam distilled or cold-pressed from flowers, fruit, bark and roots. is also the therapeutic use of aromatic su...
Gary Whipfler, Corporate Treasurer of Apple Computers gave a very informative presentation about the field of Finance from his own 13 years of experience. As an MBA graduate at Santa Clara, he returned here and gave students some excellent advice about entering the workforce. I think this was the best part of his presentation that I personally to...
means the surroundings. Land, water, air, plants, animals, solid wastes and other things that are surrounding us constitute our environment. Man and environment are closely intertwined with each other, to maintain a balance or equilibrium in nature. Different groups of people working in different areas express it in various ways. When physical sc...
(CF) used to be considered a childhood disease, because people born with it rarely lived to reach adolescence. Now, with marked improvement in treatments'from physiotherapy and antibiotics that keep the lungs clear of mucus and microbes to enzyme supplements that aid digestion'many people with CF live into their thirties and beyond (Hopkin, 1998)....
? The first attempt in cloning was conducted in 1952 on a group of frogs. The experiment was a partial success. The frog cells were cloned into other living frogs however, only one in every thousand developed normally , all of which were sterile. The rest of the frogs that survived grew to abnormally large sizes. In 1993, scientist and director...
About 2.5 billion years ago, oxygen began slowly to accumulate in the atmosphere, as a result of the photosynthetic activity of the cyanobacteria. Those prokaryotes that were able to use oxygen in ATP production gained a strong advantage, and so they began to prosper and increase. Some of these cells may have evolved into modern forms of aerobic b...
This paper looks at the controversial issue of climatic change. In particular, it develops the question of if and why earth's climate is changing? The roles of man, naturally occurring trends, and earth's cycles are considered, and an outlook for what can be expected in the near and distant future is given. 'The uneasiness of modern man arises f...