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Articles 20731 - 20760 of 20817

Full-Text Articles in Physics

Physics, Chapter 29: The Magnetic Field, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 29: The Magnetic Field, Henry Semat, Robert Katz

Robert Katz Publications

Natural magnets, called lodestones, have been known since ancient times. The lodestone, a magnetic oxide of iron called magnetite (Fe3O4), was mentioned by Thales of Miletus. By the eleventh century the magnetic compass was known to the Chinese, and in the twelfth century references to the compass were made in Western Europe. The lodestone is capable of attracting pieces of iron and of imparting permanent magnetism to other pieces of iron so that these too could attract iron filings. If an iron bar is magnetized, as the result of being near a piece of lodestone, and …

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Physics, Chapter 2: Motion Of A Particle (Kinematics), Henry Semat, Robert Katz Jan 1958

Physics, Chapter 2: Motion Of A Particle (Kinematics), Henry Semat, Robert Katz

Robert Katz Publications

Normally, when we say an object is at rest, we mean that it is at rest with respect to the surface of the earth; when we say a car is moving at a speed of 40 mi/hr, we imply that the motion is taking place at this speed relative to the road. A boat sailing on the river moves with respect to the river's banks, but it also moves with respect to the flowing water in the river. The lift on the wings of an airplane is generated by the motion of the airplane through the air, but it is …

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Physics, Chapter 9: Hydrodynamics (Fluids In Motion), Henry Semat, Robert Katz Jan 1958

Physics, Chapter 9: Hydrodynamics (Fluids In Motion), Henry Semat, Robert Katz

Robert Katz Publications

When a liquid flows through a pipe in such a way that it completely fills the pipe, and as much liquid enters one end of the pipe as leaves the other end of the pipe in the same time, then the liquid is said to flow at a steady rate. At any point of the pipe, the flow of the liquid does not change with time. The path of any particle of liquid as it moves through the pipe is called a streamline. We can map the flow of liquid through the pipe by drawing a series of …

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Physics, Chapter 4: Statics Of A Rigid Body, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 4: Statics Of A Rigid Body, Henry Semat, Robert Katz

Robert Katz Publications

In the preceding chapter we observed that a particle would remain in equilibrium, in a state of rest, or in a state of uniform motion in a straight line when the resultant of all the forces acting on it was equal to zero. This condition for equilibrium was extended to larger bodies under either of two possible conditions: If the forces acting on the body were concurrent, that is, if they were directed toward a single point, the body could be treated as if it were a particle; or if the body moved with uniform translational motion in which every …

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Physics, Chapter 17: The Phases Of Matter, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 17: The Phases Of Matter, Henry Semat, Robert Katz

Robert Katz Publications

A substance which has a definite chemical composition can exist in one or more phases, such as the vapor phase, the liquid phase, or the solid phase. When two or more such phases are in equilibrium at any given temperature and pressure, there are always surfaces of separation between the two phases.

In the solid phase a pure substance generally exhibits a well-defined crystal structure in which the atoms or molecules of the substance are arranged in a repetitive lattice. Many substances are known to exist in several different solid phases at different conditions of temperature and pressure. These …

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Physics, Chapter 45: Natural Radioactivity, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 45: Natural Radioactivity, Henry Semat, Robert Katz

Robert Katz Publications

The discovery of an important phenomenon usually leads to other important discoveries. The discovery of x-rays by Roentgen in 1895 led to the discovery of radioactivity by Becquerel in 1896. In the gas type of x-ray tube used by Roentgen, the glass walls of the tube were observed to fluoresce. Becquerel was interested in determining whether there was any relationship between the fluorescence of the glass of an x-ray tube and the phosphorescence of certain salts which were irradiated by ordinary light. One of the salts used by Becquerel was the double sulphate of uranium and potassium. He wrapped a …

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Physics, Chapter 44: Stable Nuclei, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 44: Stable Nuclei, Henry Semat, Robert Katz

Robert Katz Publications

Atomic and nuclear physics are essentially twentieth-century developments, although these had their origins at the close of the nineteenth century. These developments followed two parallel streams, as shown in Figure 44-1, one dealing with the electronic structure of the atom and the other dealing with its nuclear structure. These two streams served to feed each other and were fed by all other branches of physics, but only a few of the more important contributions concerning the nature of radiation, matter, and energy are shown in the figure.

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Physics, Chapter 42: Optical Spectra And Atomic Structure, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 42: Optical Spectra And Atomic Structure, Henry Semat, Robert Katz

Robert Katz Publications

When light passes through a prism spectroscope or a diffraction-grating spectroscope, an optical spectrum is obtained in which the intensity of the radiation may be analyzed as a function of wavelength. The spectrum may be observed visually in the limited wavelength region to which the eye is sensitive; it may be focused on a photographic plate or upon a thermocouple or thermopile. Our knowledge of the structure of atoms and molecules is largely dependent upon the analyses of optical spectra, for these spectra are characteristic of the emitting atoms or molecules. Even before the spectra of atoms were properly understood …

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Physics, Chapter 27: Direct-Current Circuits, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 27: Direct-Current Circuits, Henry Semat, Robert Katz

Robert Katz Publications

When a charged particle traverses a closed path in an electrostatic field in space, the total work done on the particle is zero. The electric field is conservative. Associated with each point in the field, there is a fixed value of the electrical potential.

In a simple circuit consisting of a chemical cell and a resistor, as shown in Figure 27-1, we have seen that the current flows through the resistor from the positive terminal of the cell to the negative terminal of the cell. The positive terminal is at the higher potential, so that the current flows from the …

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Physics, Chapter 28: Electrical Conduction In Liquids And Solids, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 28: Electrical Conduction In Liquids And Solids, Henry Semat, Robert Katz

Robert Katz Publications

We have seen that electrical conduction in solids is associated with the drift of free electrons in the solid, a process which will be examined in greater detail in Section 28-4. A similar mechanism may be used to account for the conduction of electricity in liquid metals. In other liquids electricity is conducted by the migration of positive and negative ions through the liquid.

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Physics, Chapter 10: Momentum And Impulse, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 10: Momentum And Impulse, Henry Semat, Robert Katz

Robert Katz Publications

An extremely important concept in the development of mechanics is that of momentum. The momentum of a body is defined as the product of its mass by its velocity. We shall use the symbol p to denote the momentum of a body. The momentum of a body is a vector quantity, for it is the product of mass, a scalar, by velocity, a vector. While momentum and kinetic energy are compounded of the same two ingredients, mass and velocity, they are quite different concepts, and one aspect of their difference may be seen in the fact that momentum is …

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Physics, Chapter 12: Periodic Motion, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 12: Periodic Motion, Henry Semat, Robert Katz

Robert Katz Publications

One of the more important problems in mechanics is the study of periodic motions, that is, motions which repeat themselves in regular intervals of time, called the period. An example of periodic motion which we hrNe already encountered is uniform circular motion, in which the velocity and acceleration of the body at a given angular position were always the same. If a particle was found at a given position at a time t, we could be sure that it would return to that position at time t + T later, where T was the period of the rotational motion. A …

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Physics, Chapter 21: Vibrations And Sound, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 21: Vibrations And Sound, Henry Semat, Robert Katz

Robert Katz Publications

There are two aspects of sound: one is the physical aspect which involves the physics of the production, propagation, reception, and detection of sound; the other, which is the sensation of sound as perceived by the individual, depends upon physiological and psychological effects. It is not desirable to separate the two aspects of sound completely, but the main emphasis in this book must necessarily be on the physical aspect. In this chapter we shall consider mostly musical sounds. A vocabulary has been developed to describe the sensation experienced when a musical sound is heard. Such terms as the pitch of …

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Physics, Chapter 11: Rotational Motion (The Dynamics Of A Rigid Body), Henry Semat, Robert Katz Jan 1958

Physics, Chapter 11: Rotational Motion (The Dynamics Of A Rigid Body), Henry Semat, Robert Katz

Robert Katz Publications

The motion of the flywheel of an engine and of a pulley on its axle are examples of an important type of motion of a rigid body, that of the motion of rotation about a fixed axis. Consider the motion of a uniform disk rotating about a fixed axis passing through its center of gravity C perpendicular to the face of the disk, as shown in Figure 11-1. The motion of this disk may be described in terms of the motions of each of its individual particles, but a better way to describe the motion is in terms of …

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Physics, Chapter 19: Heat Engines, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 19: Heat Engines, Henry Semat, Robert Katz

Robert Katz Publications

In this chapter we shall consider the physical principles underlying the operations of heat engines because of the intrinsic importance of these principles and because of the part they have played in the development of fundamental physical ideas. Heat engines are designed and built to convert heat into work. In most cases the heat is obtained from the combustion of a common fuel such as coal, oil, gasoline, or natural gas. An important new source of heat that is just beginning to be used, and will be used more extensively in the future, is the mass which is converted into …

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Physics, Appendix B, Henry Semat, Robert Katz Jan 1958

Physics, Appendix B, Henry Semat, Robert Katz

Robert Katz Publications

Appendix B

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Physics, Chapter 18: Transfer Of Heat, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 18: Transfer Of Heat, Henry Semat, Robert Katz

Robert Katz Publications

The methods by which heat is transmitted can be classified into three distinct types known as convection, conduction, and radiation. In any actual case of heat transmission, a combination of these methods may be operating simultaneously, and the principal problem is to determine the rate at which heat flows from the source at higher temperature to the source at lower temperature.

We may distinguish between the three processes of heat transfer by considering whether a medium is required for the transfer of heat, and whether that medium is at rest or in motion. In the process of conduction, …

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Physics, Chapter 16: Kinetic Theory Of Gases, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 16: Kinetic Theory Of Gases, Henry Semat, Robert Katz

Robert Katz Publications

The behavior of a gas under various conditions of temperature and pressure has already been studied in some detail. When the pressure of a constant mass of gas is not too great, say less than about 2 atm, we find that a gas obeys the following relationships to be discussed.

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Physics, Chapter 40: Light As A Wave Motion, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 40: Light As A Wave Motion, Henry Semat, Robert Katz

Robert Katz Publications

Let us recount some of the characteristics of the motion of particles and the propagation of waves, with a view toward analyzing the behavior of light. In accordance with Newton's first law, a particle moves in a straight-line path in the absence of external forces. Thus we might infer, as Newton suggested, that light is composed of particles, and that, in a continuous medium, there is no deflecting force on the light particles. At the interface between two media, light may be propagated in a straight line parallel to the interface. Thus even at an interface there is no force …

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Physics, Chapter 37: Reflection And Refraction, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 37: Reflection And Refraction, Henry Semat, Robert Katz

Robert Katz Publications

In the passage of a beam of light through a medium, some of the radiant energy is absorbed and is transformed into internal energy, while some of it is scattered in all directions. The oscillating electric field associated with the light wave sets some of the electrons of the medium into oscillation, thus giving up some of its energy, and these oscillating electrons subsequently reradiate energy as scattered electromagnetic radiation. Scattering therefore takes place only in the presence of matter. The color of the sky is due to the small amount of scattering of sunlight by the molecules of the …

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Physics, Chapter 36: Light And Its Measurement, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 36: Light And Its Measurement, Henry Semat, Robert Katz

Robert Katz Publications

The word light, as commonly used, refers to the radiant energy which produces a visual effect. It was first shown by Maxwell that light is an electromagnetic radiation, propagated with a speed whose value was numerically determined by the relationship between electric and magnetic units.

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Physics, Chapter 34: Alternating Currents, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 34: Alternating Currents, Henry Semat, Robert Katz

Robert Katz Publications

If the current in a resistor varies sinusoidally, as shown in Figure 34-1, the potential difference across the terminals of the resistor will also vary sinusoidally in the same manner, in phase with the current, in accordance with Ohm's law. Writing i for the instantaneous value of the current and v for the instantaneous value of the potential difference, we have v = iR.

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Physics, Chapter 32: Electromagnetic Induction, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 32: Electromagnetic Induction, Henry Semat, Robert Katz

Robert Katz Publications

When a wire moves through a uniform magnetic field of induction B, in a direction at right angles to the field and to the wire itself, the electric charges within the conductor experience forces due to their motion through this magnetic field. The positive charges are held in place in the conductor by the action of interatomic forces, but the free electrons, usually one or two per atom, are caused to drift to one side of the conductor, thus setting up an electric field E within the conductor which opposes the further drift of electrons. The magnitude of this …

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Physics, Chapter 46: Nuclear Reactions, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 46: Nuclear Reactions, Henry Semat, Robert Katz

Robert Katz Publications

One of the most important developments of twentieth-century physics was the formulation of the special theory of relativity. This theory was an outgrowth of the failure of all attempts to show that the motion of the source of light relative to the observer had any effect on the speed of light. It is impossible to account for these experimental findings of Michelson and Morley, and others, on the basis of classical mechanics and electromagnetic theory. In 1905, Albert Einstein put forth the suggestion that all experimental findings would be clarified if it were assumed that the speed of light is …

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Physics, Chapter 43: X-Rays, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 43: X-Rays, Henry Semat, Robert Katz

Robert Katz Publications

The study of the electric discharge through gases led directly to the discovery of x-rays by W. C. Roentgen in 1895. While operating a gas discharge tube, Roentgen observed that a platinum-barium cyanide screen at some distance from the tube fluoresced. He shielded the tube so that no visible radiation could reach the screen, but the fluorescence could still be observed. On interposing various materials between the tube and the screen, he found that the intensity of the fluorescence could be diminished, but that it was not completely obliterated. He interpreted these observations as being due to radiation coming from …

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Physics, Chapter 41: Polarized Light, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 41: Polarized Light, Henry Semat, Robert Katz

Robert Katz Publications

The phenomena of interference and diffraction show that light is propagated as a wave motion, but they do not show whether light is a longitudinal wave or a transverse wave. The fact that the velocity of light is the same as the velocity of radio waves and the radiation of visible light from accelerated electrons, as in a betatron, indicates that light is an electromagnetic wave. We recall from Section 20-9 that a wave can be shown to be transverse if a device can be found which will prevent passage of the wave in one orientation and will allow the …

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Physics, Appendix C, Henry Semat, Robert Katz Jan 1958

Physics, Appendix C, Henry Semat, Robert Katz

Robert Katz Publications

Appendix C: Answers to Odd-Numbered Problems

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Physics, Chapter 15: Heat And Work, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 15: Heat And Work, Henry Semat, Robert Katz

Robert Katz Publications

Until about 1750 the concepts of heat and temperature were not clearly distinguished. The two concepts were thought to be equivalent in the sense that bodies at equal temperatures were thought to "contain" equal amounts of heat. Joseph Black (1728-1799) was the first to make a clear distinction between heat and temperature. Black believed that heat was a form of matter, which subsequently came to be called caloric, and that the change in temperature of a body when caloric was added to it was associated with a property of the body which he called the capacity. Later investigators endowed caloric …

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Physics, Chapter 26: The Electric Current, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 26: The Electric Current, Henry Semat, Robert Katz

Robert Katz Publications

Electricity is the basis of our present highly technical civilization. It is the means whereby energy from various sources is delivered to the consumer in a form suitable for its conversion into the many kinds of energy demanded by him. It is through the intermediary of the electric circuit that energy is transmitted electrically from the primary source, no matter where it is situated, to the ultimate consumer wherever he desires it. A complete electric circuit contains some form of electric generator, which is essentially a device for converting other forms of energy to electrical energy, a set of conductors …

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Physics, Chapter 39: Optical Instruments, Henry Semat, Robert Katz Jan 1958

Physics, Chapter 39: Optical Instruments, Henry Semat, Robert Katz

Robert Katz Publications

The photographic camera uses a converging lens to form a real, inverted image of an object. The image is focused on a film or plate which is coated with an emulsion containing silver bromide crystals. When a few incident quanta of light are absorbed in a grain of emulsion, the grain becomes activated and developable, and when the plate is developed, the bromine is removed from each activated grain, leaving a clump of silver behind. When the plate is "fixed," the remaining emulsion is removed from the plate, so that the image is made permanent. In most cameras the converging …

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