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alternating current (ac) : flow of electric charge that periodically reverses direction | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
average power : time average of the instantaneous power over one cycle | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
bandwidth : range of angular frequencies over which the average power is greater than one-half the maximum value of the average power | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
capacitive reactance : opposition of a capacitor to a change in current | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
direct current (dc) : flow of electric charge in only one direction | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
impedance : ac analog to resistance in a dc circuit, which measures the combined effect of resistance, capacitive reactance, and inductive reactance | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
inductive reactance : opposition of an inductor to a change in current | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
phase angle : amount by which the voltage and current are out of phase with each other in a circuit | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
power factor : amount by which the power delivered in the circuit is less than the theoretical maximum of the circuit due to voltage and current being out of phase | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
quality factor : dimensionless quantity that describes the sharpness of the peak of the bandwidth; a high quality factor is a sharp or narrow resonance peak | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
resonant frequency : frequency at which the amplitude of the current is a maximum and the circuit would oscillate if not driven by a voltage source | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
rms current : root mean square of the current | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
rms voltage : root mean square of the voltage | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
step-down transformer : transformer that decreases voltage and increases current | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
step-up transformer : transformer that increases voltage and decreases current | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
transformer : device that transforms voltages from one value to another using induction | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
transformer equation : equation showing that the ratio of the secondary to primary voltages in a transformer equals the ratio of the number of turns in their windings | https://openstax.org/books/university-physics-volume-2/pages/15-key-terms |
Direct current (dc) refers to systems in which the source voltage is constant. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
Alternating current (ac) refers to systems in which the source voltage varies periodically, particularly sinusoidally. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The voltage source of an ac system puts out a voltage that is calculated from the time, the peak voltage, and the angular frequency. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
In a simple circuit, the current is found by dividing the voltage by the resistance. An ac current is calculated using the peak current (determined by dividing the peak voltage by the resistance), the angular frequency, and the time. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
For resistors, the current through and the voltage across are in phase. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
For capacitors, we find that when a sinusoidal voltage is applied to a capacitor, the voltage follows the current by one-fourth of a cycle. Since a capacitor can stop current when fully charged, it limits current and offers another form of ac resistance, called capacitive reactance, which has units of ohms. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
For inductors in ac circuits, we find that when a sinusoidal voltage is applied to an inductor, the voltage leads the current by one-fourth of a cycle. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The opposition of an inductor to a change in current is expressed as a type of ac reactance. This inductive reactance, which has units of ohms, varies with the frequency of the ac source. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
AnRLCseries circuit is a resistor, capacitor, and inductor series combination across an ac source. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The same current flows through each element of anRLCseries circuit at all points in time. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The counterpart of resistance in a dc circuit is impedance, which measures the combined effect of resistors, capacitors, and inductors. The maximum current is defined by the ac version of Ohmâs law. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
Impedance has units of ohms and is found using the resistance, the capacitive reactance, and the inductive reactance. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The average ac power is found by multiplying the rms values of current and voltage. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
Ohmâs law for the rms ac is found by dividing the rms voltage by the impedance. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
In an ac circuit, there is a phase angle between the source voltage and the current, which can be found by dividing the resistance by the impedance. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The average power delivered to anRLCcircuit is affected by the phase angle. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The power factor ranges from â1 to 1. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
At the resonant frequency, inductive reactance equals capacitive reactance. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The average power versus angular frequency plot for aRLCcircuit has a peak located at the resonant frequency; the sharpness or width of the peak is known as the bandwidth. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The bandwidth is related to a dimensionless quantity called the quality factor. A high quality factor value is a sharp or narrow peak. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
Power plants transmit high voltages at low currents to achieve lower ohmic losses in their many kilometers of transmission lines. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
Transformers use induction to transform voltages from one value to another. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
For a transformer, the voltages across the primary and secondary coils, or windings, are related by the transformer equation. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
The currents in the primary and secondary windings are related by the number of primary and secondary loops, or turns, in the windings of the transformer. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
A step-up transformer increases voltage and decreases current, whereas a step-down transformer decreases voltage and increases current. | https://openstax.org/books/university-physics-volume-2/pages/15-summary |
I d = ε 0 d Φ E d t I d = ε 0 d Φ E d t | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
â® E â · d A â = Q in ε 0 â® E â · d A â = Q in ε 0 | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
â® B â · d A â = 0 â® B â · d A â = 0 | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
â® E â · d l â = â d Φ m d t â® E â · d l â = â d Φ m d t | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
â® B â · d l â = μ 0 I + ε 0 μ 0 d Φ E d t â® B â · d l â = μ 0 I + ε 0 μ 0 d Φ E d t | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
â 2 E y â x 2 = ε 0 μ 0 â 2 E y â t 2 â 2 E y â x 2 = ε 0 μ 0 â 2 E y â t 2 | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
c = 1 ε 0 μ 0 c = 1 ε 0 μ 0 | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
c = E B c = E B | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
S â = 1 μ 0 E â à B â S â = 1 μ 0 E â à B â | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
I = S avg = c ε 0 E 0 2 2 = c B 0 2 2 μ 0 = E 0 B 0 2 μ 0 I = S avg = c ε 0 E 0 2 2 = c B 0 2 2 μ 0 = E 0 B 0 2 μ 0 | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
p = { I / c Perfect absorber 2 I / c Perfect reflector p = { I / c Perfect absorber 2 I / c Perfect reflector | https://openstax.org/books/university-physics-volume-2/pages/16-key-equations |
displacement current : extra term in Maxwellâs equations that is analogous to a real current but accounts for a changing electric field producing a magnetic field, even when the real current is present | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
gamma ray (γγray) : extremely high frequency electromagnetic radiation emitted by the nucleus of an atom, either from natural nuclear decay or induced nuclear processes in nuclear reactors and weapons; the lower end of theγγ-ray frequency range overlaps the upper end of the X-ray range, butγγrays can have the hig... | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
infrared radiation : region of the electromagnetic spectrum with a frequency range that extends from just below the red region of the visible light spectrum up to the microwave region, or from0.74μm to300μm0.74μm to300μm | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
Maxwellâs equations : set of four equations that comprise a complete, overarching theory of electromagnetism | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
microwaves : electromagnetic waves with wavelengths in the range from 1 mm to 1 m; they can be produced by currents in macroscopic circuits and devices | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
Poynting vector : vector equal to the cross product of the electric-and magnetic fields, that describes the flow of electromagnetic energy through a surface | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
radar : common application of microwaves; radar can determine the distance to objects as diverse as clouds and aircraft, as well as determine the speed of a car or the intensity of a rainstorm | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
radiation pressure : force divided by area applied by an electromagnetic wave on a surface | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
radio waves : electromagnetic waves with wavelengths in the range from 1 mm to 100 km; they are produced by currents in wires and circuits and by astronomical phenomena | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
thermal agitation : thermal motion of atoms and molecules in any object at a temperature above absolute zero, which causes them to emit and absorb radiation | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
ultraviolet radiation : electromagnetic radiation in the range extending upward in frequency from violet light and overlapping with the lowest X-ray frequencies, with wavelengths from 400 nm down to about 10 nm | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
visible light : narrow segment of the electromagnetic spectrum to which the normal human eye responds, from about 400 to 750 nm | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
X-ray : invisible, penetrating form of very high frequency electromagnetic radiation, overlapping both the ultraviolet range and theγγ-ray range | https://openstax.org/books/university-physics-volume-2/pages/16-key-terms |
Maxwellâs prediction of electromagnetic waves resulted from his formulation of a complete and symmetric theory of electricity and magnetism, known as Maxwellâs equations. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The four Maxwellâs equations together with the Lorentz force law encompass the major laws of electricity and magnetism. The first of these is Gaussâs law for electricity; the second is Gaussâs law for magnetism; the third is Faradayâs law of induction (including Lenzâs law); and the fourth is Ampèreâs law ... | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The symmetry introduced between electric and magnetic fields through Maxwellâs displacement current explains the mechanism of electromagnetic wave propagation, in which changing magnetic fields produce changing electric fields and vice versa. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
Although light was already known to be a wave, the nature of the wave was not understood before Maxwell. Maxwellâs equations also predicted electromagnetic waves with wavelengths and frequencies outside the range of light. These theoretical predictions were first confirmed experimentally by Heinrich Hertz. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
Maxwellâs equations predict that the directions of the electric and magnetic fields of the wave, and the waveâs direction of propagation, are all mutually perpendicular. The electromagnetic wave is a transverse wave. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The strengths of the electric and magnetic parts of the wave are related byc=E/B,c=E/B,which implies that the magnetic fieldBis very weak relative to the electric fieldE. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
Accelerating charges create electromagnetic waves (for example, an oscillating current in a wire produces electromagnetic waves with the same frequency as the oscillation). | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The energy carried by any wave is proportional to its amplitude squared. For electromagnetic waves, this means intensity can be expressed as | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
whereIis the average intensity inW/m2W/m2andE0E0is the maximum electric field strength of a continuous sinusoidal wave. This can also be expressed in terms of the maximum magnetic field strengthB0B0as | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
and in terms of both electric and magnetic fields as | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The three expressions forIavgIavgare all equivalent. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
Electromagnetic waves carry momentum and exert radiation pressure. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The radiation pressure of an electromagnetic wave is directly proportional to its energy density. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The pressure is equal to twice the electromagnetic energy intensity if the wave is reflected and equal to the incident energy intensity if the wave is absorbed. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The relationship among the speed of propagation, wavelength, and frequency for any wave is given byv=fλ,v=fλ,so that for electromagnetic waves,c=fλ,c=fλ,wherefis the frequency,λλis the wavelength, andcis the speed of light. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
The electromagnetic spectrum is separated into many categories and subcategories, based on the frequency and wavelength, source, and uses of the electromagnetic waves. | https://openstax.org/books/university-physics-volume-2/pages/16-summary |
c = 2.99792458 Ã 10 8 m/s â 3.00 Ã 10 8 m/s c = 2.99792458 Ã 10 8 m/s â 3.00 Ã 10 8 m/s | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
n = c v n = c v | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
θ r = θ i θ r = θ i | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
n 1 sin θ 1 = n 2 sin θ 2 n 1 sin θ 1 = n 2 sin θ 2 | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
θ c = sin â1 ( n 2 n 1 ) for n 1 > n 2 θ c = sin â1 ( n 2 n 1 ) for n 1 > n 2 | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
I = I 0 cos 2 θ I = I 0 cos 2 θ | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
tan θ b = n 2 n 1 tan θ b = n 2 n 1 | https://openstax.org/books/university-physics-volume-3/pages/1-key-equations |
birefringent : refers to crystals that split an unpolarized beam of light into two beams | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
Brewsterâs angle : angle of incidence at which the reflected light is completely polarized | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
Brewsterâs law : tanθb=n2n1tanθb=n2n1, wheren1n1is the medium in which the incident and reflected light travel andn2n2is the index of refraction of the medium that forms the interface that reflects the light | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
corner reflector : object consisting of two (or three) mutually perpendicular reflecting surfaces, so that the light that enters is reflected back exactly parallel to the direction from which it came | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
critical angle : incident angle that produces an angle of refraction of90°90° | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
direction of polarization : direction parallel to the electric field for EM waves | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
dispersion : spreading of light into its spectrum of wavelengths | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
fiber optics : field of study of the transmission of light down fibers of plastic or glass, applying the principle of total internal reflection | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
geometric optics : part of optics dealing with the ray aspect of light | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
horizontally polarized : oscillations are in a horizontal plane | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
Huygensâs principle : every point on a wave front is a source of wavelets that spread out in the forward direction at the same speed as the wave itself; the new wave front is a plane tangent to all of the wavelets | https://openstax.org/books/university-physics-volume-3/pages/1-key-terms |
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