Space exploration through Einstein's equation Even the radiation pressure that propels spacecraft to study our distant universe is made possible by Einstein's E=mc².

How did the universe come about? What is its structure like? What are the basic particles that go into the making of it? And what principles govern its operation? These big questions are worth your attention. In an effort to figure the universal order, you will also come to know the processes that have shaped planet earth.

Your exploration of the physical world around you will unravel a simple idea: all natural objects, events, and processes are interconnected in such a way that only a few concepts are needed to make sense of it all. Our endeavor is to help you get a grip of the key concepts, theories, and principles so that you know and apply the workings of nature.

The study of physics is fascinating. Trying to get a clear picture of the concepts, theories, and principles is critical, now, more than ever. Do look deep and get a clear picture of the universal order – you stand to succeed now, and in the future.

Solar system Systems' length scales are greater than atomic scale and motions are much slower than the speed of light.

In general, it is found that classical physics (mechanics, optics, acoustics, thermodynamics, and electromagnetism) works at the macroscopic (above atomic) level where: space and time are contexts in which all the physical phenomenon take place; space and time are considered absolute and that no physical phenomena can affect them; systems' length scales are greater than atomic scale and motions are much slower than the speed of light; and mechanics, electricity, and magnetism embody a continuous wave model of light.

Filling of atomic orbitals using Aufbau rule

• s orbitals have 1 possible value of m to hold 2 electrons
• p orbitals have 3 possible values of m to hold 6 electrons
• d orbitals have 5 possible values of m to hold 10 electrons
• f orbitals have 7 possible values of m to hold 14 electrons

Extending human observations of natural phenomena further, the great minds of 20^th century studied the nature and behavior of matter and energy at a very small scale. It was Rutherford who proposed that mass of an atom was concentrated in the nucleus and that the nucleus has a positive charge. He also added that the nucleus was surrounded by negatively charged electrons. Extending this model, Neils Bohr placed the electrons in a definite shell, or quantum shells. These observations led to new insights into the arrangement of electrons around nucleus and the processes by which the arrangements change. The field of atomic theory was born.

The discovery of neutron by James Chadwick, on the other hand, led to a new field called nuclear theory. This theory proposed a new type of force called nuclear force. Physicists soon had four fundamental forces in nature to contend with: strong nuclear force, weak nuclear force, gravitation, and electromagnetism. Now, the attention of physicists turned deeper into the structure of nucleons, it was Murray Gell-Mann who proposed that nucleons were composed of quarks. The deeper physicists travelled, they observed that a different picture of space, time, and matter presented itself (as compared to the classical physics). These phenomena are now well explained by advancements, in what is termed, the modern physics.

Producing electricity throw using Magnetism

• In 1831, an English scientist, Michael Faraday discovered that magnetism could produce electricity. He wrapped two insulated coils of wire, forming helices, around a massive iron ring. One helix was connected to a battery and the other to a galvanometer. Faraday believed that when a current flowed through one helix the magnetic field it created would be channelled to the other helix by means of a permeable iron ring.
• Electromagnetic induction is the complementary phenomenon to electromagnetism. Instead of producing a magnetic field from electricity, we produce electricity from a magnetic field. There is one important difference, though: whereas electromagnetism produces a steady magnetic field from a steady electric current, electromagnetic induction requires motion between the magnet and the coil to produce a voltage.

The knowledge of the physical world later expanded to include such areas as heat, sound, electricity and magnetism, followed by the idea of conservation of energy. Energy exists in many forms, such as heat, light, chemical energy, and electrical energy. Thermodynamics is the study of energy and the laws of thermodynamics govern the energy transformations. The First Law of Thermodynamics (conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another. The contribution of Rudolf Clausius is immense through his famous second law of thermodynamics which states that in any closed system, the entropy of the system will either remain constant or increase. The most efficient heat engine cycle is the Carnot cycle, consisting of two isothermal processes and two adiabatic processes and the second law of thermodynamics sets the limiting value on the efficiency of Carnot cycle.

Michael Faraday discovered the connections between the phenomena of electricity and magnetism by observing that the flow of electric charge through a wire caused magnetic effects, and a changing magnetic field could produce a current in a closed loop of wire. He summarized his historic discovery in a single statement: "Whenever a magnetic force increases or decreases, it produces electricity; the faster it increases or decreases, the more electricity it produces". Amount of electricity produced by magnetism was equal to the rate of increase or decrease of the magnetic force. It was said that Faraday has seen the world through the eyes of poet by seeing simplicity while there is complexity. And then, toward the end of the century, the great physicist James Clerk Maxwell showed how, by uniting the equations that described electric and magnetic fields, he could account for the transmission of light through space at the amazing speed of about 3 × 10⁸ meters per second, a value that was already known from experiment. The net result was a tremendous unification of physics. The Faraday's law is very significant as it changed the world leading to development of electric motors, generators and everything that works on electricity.

Electron diffraction pattern Demonstration of wave-particle duality. An electron gun has been fired at a thin sheet of graphite. The electrons passed through and hit a luminescent screen, producing the patterns of rings associated with diffraction. Diffraction occurs when a wave passes through an aperture similar in size to its wavelength. But electrons are particles, so should not exhibit the same phenomenon unless they can also behave like waves. De Broglie (1892 - 1987) correctly deduced that this was the case and that particles have wavelengths inversely proportional to their momentum.

Radiant heat from hot objects was considered a form of electromagnetic radiation, but classical theory of electromagnetic radiation could not explain this spectrum. The German physicist Max Planck (1858 - 1947) suggested that energy from a hot body could only be released in discrete amounts, proportional to the frequency (inversely proportional to the wavelength) of the emitted radiation, according to the formula E = hf ( where 'f' is the frequency and 'h' is what quickly came to be known as Planck's constant). Thus the quantum was born. Planck stopped short of proposing that the radiation itself was quantized as the classical wave theory of light still stood supreme.

The discoveries in atomic physics and radiation were enough to shake classical physics to its core, but more was to come. In 1905, Einstein came forward with his revolutionary proposal that neither time nor space was absolute, that they were related to one another, and that both depended on measurements made with respect to a chosen frame of reference, which had to be identified. This special theory of relativity was particularly troubling to the traditionalists who assumed that a hypothetical medium is essential as the carrier of light and all other kinds of electromagnetic waves. Physicists had to get used to the idea that electromagnetic waves did not need a medium to wave in.

Interference pattern The diffraction and interference effects appear at first sight to be due to the beam of electrons, interfering with each other. However, the interference pattern still results even if only one electron traverses the apparatus at a time. In this case, the pattern is built up gradually from the statistically correlated impacts on many electrons arriving independently at the detection system.

It continued to be an article of faith among most physicists that the laws of strict cause-and-effect allow us to predict, in principle, the course of all events above the atomic level.

The great French physicist Pierre Simon de Laplace articulated this belief in a famous statement: "An intelligence which, at a certain instant, knew all the forces of nature and also the situations [positions and velocities] of the entities in it, and which furthermore was capable of analyzing all these data, could encompass in the same formula the motions of the largest bodies in the universe and those of the lightest atom; to it [this intelligence] nothing would be uncertain, and the future would be as clear to it as the past."

Astronomy and Lasers The laws of physics are applied in the field of astronomy and in studying lasers.

The properties were controllable through the addition of other types of atoms called doping in semiconductors which led to the invention of the transistor. Then the whole science of solid state electronics evolved, which now dominates our communications and computer technology. Einstein proposed that the transition of an atom from its excited state to its lower state would be enhanced if it were struck by a photon of the same energy and it would lead to the appearance of two quanta of a certain energy where there had only been one before. This can lead to chain reaction stimulated by photons striking a large population of atoms in the excited state, giving rise to a big burst of radiation of the same frequency and wavelength. Based on this principle, LASER (which stands for Light Amplification by Stimulated Emission of Radiation), a beam of light of very high intensity and very small angular divergence was invented by Theodore Maiman in 1927.

Semiconductor and Nuclear reactions

• Semiconductor materials are useful because their behavior can be manipulated by the addition of impurities, known as doping.
• The actual reaction involves a deuterium nucleus fusing with a tritium nucleus to form an alpha particle (⁴He nucleus) and a neutron.

Scientists of all disciplines make use of the ideas of physics including chemists and biologists. The space travel, mobile computing and 3D experience were made possible with application of principles or laws of physics in engineering and technology. Semiconductors which led to the invention of the transistor, and then the whole science of solid state electronics, now dominate our communications and computer technology. Lasers find many applications in spectroscopy, industry, medical and defensive countermeasures. It would be a great break through for clean energy if we can create plasma of certain light elements such as hydrogen isotopes and make the system hot enough to produce nuclear fusion reactions.

Even though chemistry is now being explained in terms of electromagnetic forces and quantum theory and biology is beginning to derive valuable insights from the application of basic physical principles, physics is primarily concerned with understanding the universe, its constituent particles and their interactions at the most primitive level. Observe nature through eyes of physics, grasp the laws of nature, identify similarities and develop insight to be able to apply what you have learnt in finding solutions to challenges in making the world a better place to live.