PH 202 exam 2 and final
MAKING CONNECTIONS: CONCEPT OF A FIELD
A field is a way of mapping forces surrounding any object that can act on another object at a distance without apparent physical connection. The field represents the object generating it. Gravitational fields map gravitational forces, electric fields map electrical forces, and magnetic fields map magnetic forces.
DIVERGING LENS
A lens that causes the light rays to bend away from its axis is called a diverging lens.
RULES FOR RAY TRACING
A ray entering a converging lens parallel to its axis passes through the focal point F of the lens on the other side. A ray entering a diverging lens parallel to its axis seems to come from the focal point F. A ray passing through the center of either a converging or a diverging lens does not change direction. A ray entering a converging lens through its focal point exits parallel to its axis. A ray that enters a diverging lens by heading toward the focal point on the opposite side exits parallel to the axis.
Step up and step down
A step-up transformer is one that increases voltage, whereas a step-down transformer decreases voltage.
THIN LENS
A thin lens is defined to be one whose thickness allows rays to refract but does not allow properties such as dispersion and aberrations.
Current: The Source of All Magnetism
An electromagnet creates magnetism with an electric current. In later sections we explore this more quantitatively, finding the strength and direction of magnetic fields created by various currents. But what about ferromagnets? Figure 22.13 shows models of how electric currents create magnetism at the submicroscopic level. (Note that we cannot directly observe the paths of individual electrons about atoms, and so a model or visual image, consistent with all direct observations, is made. We can directly observe the electron's orbital angular momentum, its spin momentum, and subsequent magnetic moments, all of which are explained with electric-current-creating subatomic magnetism.) Currents, including those associated with other submicroscopic particles like protons, allow us to explain ferromagnetism and all other magnetic effects. Ferromagnetism, for example, results from an internal cooperative alignment of electron spins, possible in some materials but not in others.
VIRTUAL IMAGE
An image that is on the same side of the lens as the object and cannot be projected on a screen is called a virtual image.
making iron a magnet
An unmagnetized piece of iron is placed between two magnets, heated, and then cooled, or simply tapped when cold. The iron becomes a permanent magnet with the poles aligned as shown: its south pole is adjacent to the north pole of the original magnet, and its north pole is adjacent to the south pole of the original magnet. Note that there are attractive forces between the magnets.
Tansformer
Changes one voltage to another
combinning ferromagnets with electromagnets
Combining a ferromagnet with an electromagnet can produce particularly strong magnetic effects. Whenever strong magnetic effects are needed, such as lifting scrap metal, or in particle accelerators, electromagnets are enhanced by ferromagnetic materials. Limits to how strong the magnets can be made are imposed by coil resistance (it will overheat and melt at sufficiently high current), and so superconducting magnets may be employed. These are still limited, because superconducting properties are destroyed by too great a magnetic field.
What is the source of all magnetism?
Current
What property of light is responsible for the different colors?
Diffferent colors have different frequencies
DISPERSION
Dispersion is defined to be the spreading of white light into its full spectrum of wavelengths.
Electromagnets
Early in the 19th century, it was discovered that electrical currents cause magnetic effects. The first significant observation was by the Danish scientist Hans Christian Oersted (1777-1851), who found that a compass needle was deflected by a current-carrying wire. This was the first significant evidence that the movement of charges had any connection with magnets. Electromagnetism is the use of electric current to make magnets. These temporarily induced magnets are called electromagnets. Electromagnets are employed for everything from a wrecking yard crane that lifts scrapped cars to controlling the beam of a 90-km-circumference particle accelerator to the magnets in medical imaging machines shows that the response of iron filings to a current-carrying coil and to a permanent bar magnet. The patterns are similar. In fact, electromagnets and ferromagnets have the same basic characteristics—for example, they have north and south poles that cannot be separated and for which like poles repel and unlike poles attract.
MISCONCEPTION ALERT: EARTH'S MAGNETIC POLES
Earth acts like a very large bar magnet with its south-seeking pole near the geographic North Pole. That is why the north pole of your compass is attracted toward the geographic north pole of Earth—because the magnetic pole that is near the geographic North Pole is actually a south magnetic pole! Confusion arises because the geographic term "North Pole" has come to be used (incorrectly) for the magnetic pole that is near the North Pole. Thus, "north magnetic pole" is actually a misnomer—it should be called the south magnetic pole.
MAKING CONNECTIONS: RELATIVITY
Hearing all we do about Einstein, we sometimes get the impression that he invented relativity out of nothing. On the contrary, one of Einstein's motivations was to solve difficulties in knowing how different observers see magnetic and electric fields.
Inductors
Induction is the process in which an emf is induced by changing magnetic flux. Many examples have been discussed so far, some more effective than others. Transformers, for example, are designed to be particularly effective at inducing a desired voltage and current with very little loss of energy to other forms. Is there a useful physical quantity related to how "effective" a given device is? The answer is yes, and that physical quantity is called inductance
current
Infinite-length straight wires are impractical and so, in practice, a current balance is constructed with coils of wire separated by a few centimeters. Force is measured to determine current. This also provides us with a method for measuring the coulomb. We measure the charge that flows for a current of one ampere in one second. That is, 1 C=1 A⋅ssize 12{1`C=1`A cdot s} {}. For both the ampere and the coulomb, the method of measuring force between conductors is the most accurate in practice.
UNIVERSAL CHARACTERISTICS OF MAGNETS AND MAGNETIC POLES
It is a universal characteristic of all magnets that like poles repel and unlike poles attract. (Note the similarity with electrostatics: unlike charges attract and like charges repel.) Further experimentation shows that it is impossible to separate north and south poles in the manner that + and − charges can be separated.
KIRCHHOFF'S RULES
Kirchhoff's first rule—the junction rule. The sum of all currents entering a junction must equal the sum of all currents leaving the junction. Kirchhoff's second rule—the loop rule. The algebraic sum of changes in potential around any closed circuit path (loop) must be zero.
Can Kirchhoff's rules be applied to simple series and parallel circuits or are they restricted for use in more complicated circuits that are not combinations of series and parallel?
Kirchhoff's rules can be applied to any circuit since they are applications to circuits of two conservation laws. Conservation laws are the most broadly applicable principles in physics. It is usually mathematically simpler to use the rules for series and parallel in simpler circuits so we emphasize Kirchhoff's rules for use in more complicated situations. But the rules for series and parallel can be derived from Kirchhoff's rules. Moreover, Kirchhoff's rules can be expanded to devices other than resistors and emfs, such as capacitors, and are one of the basic analysis devices in circuit analysis.
lenz concervation of energy
Lenz's law is a manifestation of the conservation of energy. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy. Energy can enter or leave, but not instantaneously. Lenz's law is a consequence. As the change begins, the law says induction opposes and, thus, slows the change. In fact, if the induced emf were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated.
MAKING CONNECTIONS: UNIFICATION OF FORCES
Maxwell's complete and symmetric theory showed that electric and magnetic forces are not separate, but different manifestations of the same thing—the electromagnetic force. This classical unification of forces is one motivation for current attempts to unify the four basic forces in nature—the gravitational, electrical, strong, and weak nuclear forces.
Can any arbitrary combination of resistors be broken down into series and parallel combinations? See if you can draw a circuit diagram of resistors that cannot be broken down into combinations of series and parallel.
No, there are many ways to connect resistors that are not combinations of series and parallel, including loops and junctions. In such cases Kirchhoff's rules, to be introduced in Kirchhoff's Rules, will allow you to analyze the circuit.
Ferromagnets
Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. Such materials are called ferromagnetic, after the Latin word for iron, ferrum. A group of materials made from the alloys of the rare earth elements are also used as strong and permanent magnets; a popular one is neodymium. Other materials exhibit weak magnetic effects, which are detectable only with sensitive instruments. Not only do ferromagnetic materials respond strongly to magnets (the way iron is attracted to magnets), they can also be magnetized themselves—that is, they can be induced to be magnetic or made into permanent magnets.
When is the potential difference across a capacitor an emf?
Only when the current being drawn from or put into the capacitor is zero. Capacitors, like batteries, have internal resistance, so their output voltage is not an emf unless current is zero. This is difficult to measure in practice so we refer to a capacitor's voltage rather than its emf. But the source of potential difference in a capacitor is fundamental and it is an emf.
RAINBOWS
Rainbows are produced by a combination of refraction and reflection.
Digital meters are able to detect smaller currents than analog meters employing galvanometers. How does this explain their ability to measure voltage and current more accurately than analog meters?
Since digital meters require less current than analog meters, they alter the circuit less than analog meters. Their resistance as a voltmeter can be far greater than an analog meter, and their resistance as an ammeter can be far less than an analog meter.
Hertz's Observations
The German physicist Heinrich Hertz (1857-1894) was the first to generate and detect certain types of electromagnetic waves in the laboratory. Starting in 1887, he performed a series of experiments that not only confirmed the existence of electromagnetic waves, but also verified that they travel at the speed of light.
THE LAW OF REFLECTION
The angle of reflection equals the angle of incidence.
CONNECTIONS: WAVES AND PARTICLES
The behavior of electromagnetic radiation clearly exhibits wave characteristics. But we shall find in later modules that at high frequencies, electromagnetic radiation also exhibits particle characteristics. These particle characteristics will be used to explain more of the properties of the electromagnetic spectrum and to introduce the formal study of modern physics. Another startling discovery of modern physics is that particles, such as electrons and protons, exhibit wave characteristics. This simultaneous sharing of wave and particle properties for all submicroscopic entities is one of the great symmetries in nature.
REFRACTION
The changing of a light ray's direction (loosely called bending) when it passes through variations in matter is called refraction.
cladding
The cladding prevents light from being transmitted between fibers in a bundle.
CONNECTIONS: CONSERVATION LAWS
The derivations of the expressions for series and parallel resistance are based on the laws of conservation of energy and conservation of charge, which state that total charge and total energy are constant in any process. These two laws are directly involved in all electrical phenomena and will be invoked repeatedly to explain both specific effects and the general behavior of electricity.
Lenz's Law
The direction of an induced current is such that it'll oppose the change causing it. Lenz's law is named after Heinrich Lenz, and it says: An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the change in original magnetic flux. ... The direction of the induced emf is always such as to result in opposition to the change producing it.
FOCAL LENGTH f
The distance from the center of the lens to its focal point is called focal length fsize 12{f} {}.
REAL IMAGE
The image in which light rays from one point on the object actually cross at the location of the image and can be projected onto a screen, a piece of film, or the retina of an eye is called a real image.
Critical Angle
The incident angle θ1size 12{θ rSub { size 8{1} } } {} that produces an angle of refraction of 90ºsize 12{"90"°} {} is called the critical angle, θcsize 12{θ rSub { size 8{1} } } {}.
CONVERGING OR CONVEX LENS
The lens in which light rays that enter it parallel to its axis cross one another at a single point on the opposite side with a converging effect is called converging lens.
Ampere's Law and Others
The magnetic field of a long straight wire has more implications than you might at first suspect. Each segment of current produces a magnetic field like that of a long straight wire, and the total field of any shape current is the vector sum of the fields due to each segment. The formal statement of the direction and magnitude of the field due to each segment is called the Biot-Savart law. Integral calculus is needed to sum the field for an arbitrary shape current. This results in a more complete law, called Ampere's law, which relates magnetic field and current in a general way. Ampere's law in turn is a part of Maxwell's equations, which give a complete theory of all electromagnetic phenomena. Considerations of how Maxwell's equations appear to different observers led to the modern theory of relativity, and the realization that electric and magnetic fields are different manifestations of the same thing. Most of this is beyond the scope of this text in both mathematical level, requiring calculus, and in the amount of space that can be devoted to it. But for the interested student, and particularly for those who continue in physics, engineering, or similar pursuits, delving into these matters further will reveal descriptions of nature that are elegant as well as profound. In this text, we shall keep the general features in mind, such as RHR-2 and the rules for magnetic field lines listed in Magnetic Fields and Magnetic Field Lines, while concentrating on the fields created in certain important situations.
THE AMPERE
The official definition of the ampere is: One ampere of current through each of two parallel conductors of infinite length, separated by one meter in empty space free of other magnetic fields, causes a force of exactly 2×10−7N/msize 12{2 times "10" rSup { size 8{ - 7} } " N/m"} {} on each conductor.
GEOMETRIC OPTICS
The part of optics dealing with the ray aspect of light is called geometric optics.
FOCAL POINT F
The point at which the light rays cross is called the focal point F of the lens.
POWER P
The power Psize 12{P} {} of a lens is defined to be the inverse of its focal length. In equation form, this is P=1f.size 12{P= { {1} over {f} } } {}
MAJOR FEATURES OF RESISTORS IN SERIES
The same current flows through each resistor in series. Individual resistors in series do not get the total source voltage, but divide it.
SPEED OF LIGHT
The speed of light csize 12{c} {} not only affects refraction, it is one of the central concepts of Einstein's theory of relativity. As the accuracy of the measurements of the speed of light were improved, csize 12{c} {} was found not to depend on the velocity of the source or the observer. However, the speed of light does vary in a precise manner with the material it traverses. These facts have far-reaching implications, as we will see in Special Relativity. It makes connections between space and time and alters our expectations that all observers measure the same time for the same event, for example. The speed of light is so important that its value in a vacuum is one of the most fundamental constants in nature as well as being one of the four fundamental SI units.
the index of refraction
The speed of light depends strongly on the type of material, since its interaction with different atoms, crystal lattices, and other substructures varies. We define the index of refraction nsize 12{n} {} of a material to be
RAY
The word "ray" comes from mathematics and here means a straight line that originates at some point.
UNIFICATION OF FORCES
There are many connections between the electric force and the magnetic force. The fact that a moving electric field produces a magnetic field and, conversely, a moving magnetic field produces an electric field is part of why electric and magnetic forces are now considered to be different manifestations of the same force. This classic unification of electric and magnetic forces into what is called the electromagnetic force is the inspiration for contemporary efforts to unify other basic forces. Attempt to describe the fundamental forces of nature in the same mathematical form. The forces then act the same when the energy per particle involved is very high
WAVES
There are many types of waves, such as water waves and even earthquakes. Among the many shared attributes of waves are propagation speed, frequency, and wavelength. These are always related by the expression vW=fλsize 12{v rSub { size 8{W} } =fλ} {}. This module concentrates on EM waves, but other modules contain examples of all of these characteristics for sound waves and submicroscopic particles.
MAKING CONNECTIONS: CHARGES AND MAGNETS
There is no magnetic force on static charges. However, there is a magnetic force on moving charges. When charges are stationary, their electric fields do not affect magnets. But, when charges move, they produce magnetic fields that exert forces on other magnets. When there is relative motion, a connection between electric and magnetic fields emerges—each affects the other.
ELECTROMAGNETIC SPECTRUM: RULES OF THUMB
Three rules that apply to electromagnetic waves in general are as follows: High-frequency electromagnetic waves are more energetic and are more able to penetrate than low-frequency waves. High-frequency electromagnetic waves can carry more information per unit time than low-frequency waves. The shorter the wavelength of any electromagnetic wave probing a material, the smaller the detail it is possible to resolve. Note that there are exceptions to these rules of thumb.
Energy Stored in an Inductor
We know from Lenz's law that inductances oppose changes in current. There is an alternative way to look at this opposition that is based on energy. Energy is stored in a magnetic field. It takes time to build up energy, and it also takes time to deplete energy; hence, there is an opposition to rapid change. In an inductor, the magnetic field is directly proportional to current and to the inductance of the device. Self-Explanatory; calculated by Eind = 1/2LI^2
These statements about magnets are false.
When a magnet is broken in half, you end up with with a south and north pole magent heating a magnet makes it stronger when two nearby electrons in a material have opposite spines, their contributions to the local magnetic field tend to add up
AC VOLTAGE IN A CAPACITOR
When a sinusoidal voltage is applied to a capacitor, the voltage follows the current by one-fourth of a cycle, or by a 90º phase angle.
AC VOLTAGE IN A RESISTOR
When a sinusoidal voltage is applied to a resistor, the voltage is exactly in phase with the current—they have a 0º phase angle.
AC VOLTAGE IN AN INDUCTOR
When a sinusoidal voltage is applied to an inductor, the voltage leads the current by one-fourth of a cycle, or by a 90º phase angle.
CALCULATING MAGNETIC FORCE: EARTH'S MAGNETIC FIELD ON A CHARGED GLASS ROD
With the exception of compasses, you seldom see or personally experience forces due to the Earth's small magnetic field. To illustrate this, suppose that in a physics lab you rub a glass rod with silk, placing a 20-nC positive charge on it. Calculate the force on the rod due to the Earth's magnetic field, if you throw it with a horizontal velocity of 10 m/s due west in a place where the Earth's field is due north parallel to the ground. (The direction of the force is determined with right hand rule 1
laser vision correction
a medical procedure used to correct astigmatism and eyesight deficiencies such as myopia and hyperopia
compound microscope
a microscope constructed from two convex lenses, the first serving as the ocular lens(close to the eye) and the second serving as the objective lens
numerical aperture
a number or measure that expresses the ability of a lens to resolve fine detail in an object being observed. Derived by mathematical formula NA=nsinα,size 12{ ital "NA"=n"sin"α} {} 26.28 where nsize 12{n} {} is the refractive index of the medium between the lens and the specimen and α=θ/2
color constancy
a part of the visual perception system that allows people to perceive color in a variety of conditions and to see some consistency in the color
angular magnification
a ratio related to the focal lengths of the objective and eyepiece and given as M=−fofe
myopia
a visual defect in which distant objects appear blurred because their images are focused in front of the retina rather than being focused on the retina
farsightedness
another term for hyperopia, the condition of an eye where incoming rays of light reach the retina before they converge into a focused image
nearsightedness
another term for myopia, a visual defect in which distant objects appear blurred because their images are focused in front of the retina rather than being focused on the retina
A proton traveling to the right enters a region of uniform magnetic field that points into the plane of the screen, when the proton enter this region it will be what?
deflected towards the top of the screen
aberration
failure of rays to converge at one focus because of limitations or defects in a lens or mirror
A bar magnet is dropped through a solinoid north side down and then pulled upward through the solenoid, what is the direction of the induced current measure in the ammete?
first down then up
A bar magnet is dropped through a solinoid north side down, what would an ammeter read as the magnet falls through the solenoid?
first down, then up
hues
identity of a color as it relates specifically to the spectrum
A positive charge moving downward in an electric field that points into the screen. What is the direction of the force?
into the screen.
Mutual inductance
is the effect of Faraday's law of induction for one device upon another, such as the primary coil in transmitting energy to the secondary in a transformer. the ability of one circuit to induce an emf in a nearby circuit in the presence of a changing current
Ray tracing
is the technique of determining or following (tracing) the paths that light rays take. For rays passing through matter, the law of refraction is used to trace the paths.
What is true about light?
it is electric and magnetic fields that oscillate perpendicularly to each other its propegation direction is parallel to both the electric field and the magnetic field it moves at a constant speed through a vacuum the speed of light in matter is less than it is in a vacuum
These statements are true about magnitism
opposite poles attract Dropping makes them weaker Magnetic dominance are present in an unmagnetized piece of iron Every electron in an atom behaves like a tine magnet
adaptive optics
optical technology in which computers adjust the lenses and mirrors in a device to correct for image distortions
What type of waves require a medium to pass through?
sound waves
Current through series resistors does what?
stay the same through both
accommodation
the ability of the eye to adjust its focal length is known as accommodation
hyperopia
the condition of an eye where incoming rays of light reach the retina before they converge into a focused image
eyepiece
the lens or combination of lenses in an optical instrument nearest to the eye of the observer
far point
the object point imaged by the eye onto the retina in an unaccommodated eye
near point
the point nearest the eye at which an object is accurately focused on the retina at full accommodation
astigmatism
the result of an inability of the cornea to properly focus an image onto the retina
What happens with voltage whem it comes to resistors in series?
the voltage through the first resistor in series has the highest voltage
A positive charge movingg downward in a mgnetic field that points into the screen. What is the direction of the force?
to the right
A transformer in an AC electrical circuit may be used to "step down" what?
voltage
A negative charge moving to the right in a magnetic field that points to the right. What is the direction of the force?
zero force
