Science Article

1.a Contribution of Scientists In Atomic Model

Below are the scientist who plays big role toward the development of a scientific model of atom.

YEAR MODEL
400bc The Greek model. (democritus)-matter could not be divided into
smaller and smaller pieces


1803 The Dalton model. (John Dalton)-all elements are composed of
indivisible particles


1897 The Thomson model (J.J Thomson)-positively charged material
with negatively charged electrons scattering through it

1908 The Rutherford model (Ernest Rutherford)-small positive nucleus

1913 The Bohr model (Niels Bohr)-electrons move in a specific energy
level. The Wave model-the small positively charged nucleus is
surrounded by empty space

1918 Max Karl Erns Ludwig Planck-discovery of energy quanta

1932 Werner Heisenberg-creation of quantum mechanics

1933 Erwin Schrodinger-discovery of new productive forms of atomic
theory

1945 Wolfgang Pauli-discovery of the Exclusion principle

Democritus

Democritus may not have been the first of the ancient Greeks to suggest an atomic theory, this distinction goes to his teacher Leucippus, but his name is often associated with the first atomic theory, because of his support of it. To Democritus, atoms were completely solid, homogeneous, indestructible objects.

Dalton Atomic theory

In 1800, Dalton became a secretary of the Manchester Literary and Philosophical Society, and in the following year he orally presented an important series of papers, entitled "Experimental Essays" on the constitution of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. These four essays were published in the Memoirs of the Lit & Phil in 1802.

The second of these essays opens with the striking remark,

There can scarcely be a doubt entertained respecting the reducibility of all elastic fluids of whatever kind, into liquids; and we ought not to despair of affecting it in low temperatures and by strong pressures exerted upon the unmixed gases further.

After describing experiments to ascertain the pressure of steam at various points between 0° and 100°C (32° and 212°F), Dalton concluded from observations on the vapour pressure of six different liquids, that the variation of vapour pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapour of any given pressure.

Joseph John Thompson

Joseph John Thomson was born in 1856 in Cheetham Hill, Manchester in England, of Scottish parentage. Joseph John Thomson subjected cathode rays to magnetic and electric fields and showed that the beam was deflected as would be expected for negatively charged particles. He calculated the ratio of the electron's charge to its mass. On April 30, 1897, Thomson announced that the cathode rays consisted of negatively charged particles, which represented fundamental particles of matter. He was not the first person to suggest that these particles existed, nor did he coin the term "electron", yet he is

generally credited with the discovery of the electron. He was awarded with the Nobel Prize in Physics in 1906.

J.J. Thomson is also remembered for his "plum-pudding" model of the atom, which suggested a solid atom with positively and negatively charged particles evenly distributed throughout the mass of the atom.

Rutherfold

In 1911, Rutherford cooked up a new model of the atom in which all of the positive charge is crammed inside a tiny, massive nucleus about ten thousand times smaller than the atom as a whole. That's equivalent to a marble in the middle of a football stadium. The much lighter electrons, he assumed, lay well outside the nucleus. To the shock and amazement of everyone, the atoms of which planets, people, pianos, and everything else are made consisted almost entirely of empty space.

Rutherford's nuclear model of the atom was a huge step forward in understanding nature at the ultrasmall scale. Since the nucleus and its retinue of electrons are oppositely charged, and therefore attract one another, there didn't seem anything to stop the electrons from being pulled immediately into the nucleus. Throughout the universe, atomic matter ought to implode in the wink of an eye.

Neils Bohr

In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherford–Bohr model.

James Chadwick

Chadwick was born in Bollington, Cheshire to John Joseph Chadwick and Annie Mary née Knowles. He went to Bollington Cross C of E Primary School, attended the Central Grammar School for Boys in Manchester and then studied at the Universities of Manchester and CambridgeIn 1932, Chadwick made a fundamental discovery in the domain of nuclear science: he discovered the particle in the nucleus of an atom that became known as the neutron because it has no electric charge. In contrast with the helium nuclei (alpha particles) which are positively charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any Coulomb barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. In this way, Chadwick prepared the way towards the fission of uranium 235. For this important discovery he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935.

Max Karl Eanst Ludwig Planck

Borned in 1858 died 1947, his experimental known as black body Planck's first proposed solution to the problem in 1899 followed from what Planck called the "principle of elementary disorder", which allowed him to derive Wien's law from a number of assumptions about the entropy of an ideal oscillator, creating what was referred-to as the Wien-Planck law. Soon it was found that experimental evidence did not confirm the new law at all, to Planck's frustration. Planck revised his approach, deriving the first version of the famous Planck black-body radiation law, which described the experimentally observed black-body spectrum well. It was first proposed in a meeting of the DPG on October 19, 1900 and published in 1901. I was ready to sacrifice any of my previous convictions about physics. The central assumption behind his new derivation, presented to the DPG on 14 December 1900, was the supposition that electromagnetic energy could be emitted only in quantized form, in other words, the energy could only be a multiple of an elementary unit E = hν, where h is Planck's constant, also known as Planck's action quantum (introduced already in 1899), and ν is the frequency of the radiation.

Erwin Rudolf Josef Alexander Schrödinger ( 12 August 1887 – 4 January 1961)

This model of the atom was devised by Erwin Schrodinger. Schrodinger, along with other scientists pursuing to develop a theory of the atom that used three-dimensional standing waves to describe the orbits of electrons, worked out the details of a theory we call "quantum mechanics." In contrast in the Bohr model of the hydrogen atom, this model was much more complete, but still kept the basic features of Bohr's idea of how the hydrogen spectrum is produced. According to the theory of quantum mechanics, the orbits are not simple curves, but are three dimensional probability distributions of standing waves. These distributions describe the probability of finding electrons at certain distances from the nucleus. Darker, high density (also high probability) areas are consistent with the Bohr model.

Wolfgang Pauli

The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925. It states that no two identical fermions may occupy the same quantum state simultaneously. A more rigorous statement of this principle is that, for two identical fermions, the total wave function is anti-symmetric. For electrons in a single atom, it states that no two electrons can have the same four quantum numbers, that is, if n, l, and m_l are the same, m_s must be different such that the electrons have opposite spins.

In relativistic quantum field theory, the Pauli principle follows from applying a rotation operator in imaginary time to particles of half-integer spin. It does not follow from any spin relation in nonrelativistic quantum mechanics

1b. Magnetic field

A magnetic field is a vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.

For the physics of magnetic materials, see magnetism and magnet, and more specifically ferromagnetism, paramagnetism, and diamagnetism. For constant magnetic fields, such as are generated by magnetic materials and steady currents, see magnetostatics. A changing electric field results in a magnetic field, and a changing magnetic field also generates a electric field (see electromagnetism).

In special relativity, the electric field and magnetic field are two interrelated aspects of a single object, called the electromagnetic field. A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a moving reference frame. magnetic field is the term used in physics to describe the invisible forces in the space around a magnet, which pull on iron and other magnets. Mathematically, it is a vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.

For the physics of magnetic materials, see magnetism and magnet, and more specifically ferromagnetism, paramagnetism and diamagnetism. For constant magnetic fields, such as are generated by magnetic materials and steady currents, see magnetostatics. A changing electric field results in a magnetic field, and a changing magnetic field also generates a electric field (see electromagnetism).

In special relativity, the electric field and magnetic field are two interrelated aspects of a single object, called the electromagnetic field. A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a moving reference frame.

Magnetism

There is a strong connection between electricity and magnetism. With electricity, there are positive and negative charges. With magnetism, there are north and south poles. Similar to charges, like magnetic poles repel each other, while unlike poles attract.

An important difference between electricity and magnetism is that in electricity it is possible to have individual positive and negative charges. In magnetism, north and south

poles are always found in pairs. Single magnetic poles, known as magnetic monopoles, have been proposed theoretically, but a magnetic monopole has never been observed.

In the same way that electric charges create electric fields around them, north and south poles will set up magnetic fields around them. Again, there is a difference. While electric field lines begin on positive charges and end on negative charges, magnetic field lines are closed loops, extending from the south pole to the north pole and back again (or, equivalently, from the north pole to the south pole and back again). With a typical bar magnet, for example, the field goes from the north pole to the south pole outside the magnet, and back from south to north inside the magnet.

Electric fields come from charges. So do magnetic fields, but from moving charges, or currents, which are simply a whole bunch of moving charges. In a permanent magnet, the magnetic field comes from the motion of the electrons inside the material, or, more precisely, from something called the electron spin. The electron spin is a bit like the Earth spinning on its axis.

The magnetic field is a vector, the same way the electric field is. The electric field at a particular point is in the direction of the force a positive charge would experience if it were placed at that point. The magnetic field at a point is in the direction of the force a north pole of a magnet would experience if it were placed there. In other words, the north pole of a compass points in the direction of the magnetic field.

1b. The magnetic field produced by currents in wires

The simplest current we can come up with is a current flowing in a straight line, such as along a long straight wire. The magnetic field from a such current-carrying wire actually wraps around the wire in circular loops, decreasing in magnitude with increasing distance from the wire. To find the direction of the field, you can use your right hand. If you curl your fingers, and point your thumb in the direction of the current, your fingers will point in the direction of the field.

To determine the direction of the magnet field around a wire, the right-hand grip rule is used. When the thumb point along the direction of current, the fingers wrapped around the wire point to the direction of the magnetic field.

Experiment 1

Aims

1. To study the pattern of the magnetic field around a bar magnet using iron filing.

2. to plot the direction of the magnet field lines around a bar magnet usin compass.

Apparatus

Bar magnet and compass

Materials

Iron filings, manila cardboard, blank paper, pencil and textbook

Procedure

1. Put apiece of manila cardboard on the top of the book.

2. Place a bar magnet under the manila card.

3. sprinkle iron filing evenly on the manila card.

4. Tap the card gently with your finger gto scatter the iron filings.

5. Observe and draw the pattern of the magnetic field formed by the iron filings on the cardboard.

6. Place a compass at position on the manila cardboard.

7. Indicate the direction of magnetic field on the diagram that you have draw.

Experiment 2

Aim

To study the pattern of the magnet field produced by a straight wire carrying electric current.

Apparatus

Electric source (2V d.c.), compass, retort stand with two clamps.

Materials

Straight copper wire, connecting wire with crocodile clip, manila cardboard and iron filing.

Procedure

1. set up the apparatus correctly.

2. Sprinkle iron filing evenly on the cardboard. Observe the pattern of the scattered iron filings on the cardboard.

3. Turn on the switch. Observe and draw the patternof the magnetic field formed by the iron filingson the manila cardboard.

4. Place the compass on the manila card.

5. Observe and draw a diagram to show the compass needlein each of the compass.

ii. Reflection of the activity

1. Pupil able to answer the experiment correctly because they had learnt the topic in the class room.

2. Pupil need more time to set up the apparatus.

3. Teacher need to guide the student to make sure effective of the finding.

iii. Method employed to understand student understanding.

1. Teacher to post oral questions to student.

2. Teacher prepare a set of the question to be answered by the student.

3. Pupil to discuss their finding to the class.

4. Pupils need to write a report of the experiment.

Question need to answer by the student

1. Does a piece of straight copper wire produce a magnetic effect when it carry electric current?

…………………………………………………………………………….

2. Describe the condition under which an electric conductor will produce a magnetic effect.

………………………………………………………………………….

3.0 Asteroids

Ateroid are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago. More likely, asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across -- less than half the diameter of our Moon.

Much of our understanding about asteroids comes from examining pieces of space debris that fall to the surface of Earth. Asteroids that are on a collision course with Earth are called meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite.

Of all the meteorites examined, 92.8 percent are composed of silicate (stone), and 5.7 percent are composed of iron and nickel; the rest are a mixture of the three materials. Stony meteorites are the hardest to identify since they look very much like terrestrial rocks.

Because asteroids are material from the very early solar system, scientists are interested in their composition. Spacecraft that have flown through the asteroid belt have found that the belt is really quite empty and that asteroids are separated by very large distances. Before 1991 the only information obtained on asteroids was though Earth based observations. Then on October 1991 asteroid 951 Gaspra was visited by the Galileo

spacecraft and became the first asteroid to have hi-resolution images taken of it. Again on August 1993 Galileo made a close encounter with asteroid 243 Ida. This was the second

asteroid to be visited by spacecraft. Both Gaspra and Ida are classified as S-type asteroids composed of metal-rich silicates.

On June 27, 1997 the spacecraft NEAR made a high-speed close encounter with asteroid 253 Mathilde. This encounter gave scientists the first close-up look of a carbon rich C-type asteroid. This visit was unique because NEAR was not designed for flyby encounters. NEAR is an orbiter destined for asteroid Eros in January of 1999.

Astronomers have studied a number of asteroids through Earth-based observations. Several notable asteroids are Toutatis, Castalia, Geographos and Vesta. Astronomers studied Toutatis, Geographos and Castalia using Earth-based radar observations during close approaches to the Earth. Vesta was observed by the Hubble Space Telescope.

Meteoroid

A meteor (possibly two) and Milky way.

The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom." The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across. The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids (see also interplanetary dust).

The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectory and the light spectra of the resulting meteor. Their effects on radio signals also yield information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic.

The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with

density about a quarter that of ice to nickel-iron rich dense rocks. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs. Millions of meteors occur in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles (65 and 120 kilometers) above the earth. They disintegrate at altitudes of 30 to 60 miles (50 to 95 kilometers).

Meteor

Comet 17P/Holmes and Geminid.

A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km.

For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres)^[ the visibility is due to the air friction that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporized meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second.

Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause.

Meteorite

Main article: meteorite

A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and impact with the ground without being destroyed. Meteorites are sometimes, but not always, found in association with hypervelocity impact craters; during energetic collisions, the entire impactor may be vaporized, leaving no meteorites.

Tektite

Main article: tektite

Two tektites.

Molten terrestrial material "splashed" from a meteorite impact crater can cool and solidify into an object known as a tektite. These are often mistaken for meteorites.

Meteoric dust

Most meteoroids are destroyed when they enter the atmosphere. The left-over debris is called meteoric dust or just meteor dust. Meteor dust particles can persist in the atmosphere for up to several months. These particles might affect climate, both by scattering electromagnetic radiation and by catalyzing chemical reactions in the upper atmosphere.

Closure

Today life without electricity is unimagined. Most of the thing we do need electricity or it derive from the electricity work. People should thank to the invention of the electricity. Student should understand the matter. This is what the importance of this topic all about. Modern science is the window of tomorrow. Student should prepare themselves to learn science. Subject science should be taught in fun and interesting ways. It will make science is easier.