# Shared Flashcard Set

## Details

Chapter 4-Alternating Current
Instrumentation and Electroacoustics
29
Audiology
03/15/2017

Term
 The power source of choice for most of our small appliances (e.g., mobile phones, lamps, portable media players) is ___ ___ and some of our audiologic devices (e.g., sound-level meters, otoscopes, hearing aids)
Definition
 direct current (DC)
Term
 Some sources of power such as rotary electromechanical generators produce voltages that ___ polarity (between negative and positive) periodically over time. The voltage and the associated current alternate between ___ and ___ polarity, increasing from zero to a maximum peak in the positive direction, decreasing to zero and then increasing to a maximum peak in the opposite (negative) direction, and then returning to zero. This kind of electrical current is called ___ ___
Definition
 switch; positive; negative; alternating current (AC)
Term
 What kind of current is the main power supply in our homes?
Definition
 AC
Term
 What are some audiologic devices that use AC?
Definition
 audiometers, acoustic admittance meters, and instrumentation used to measure auditory evoked potentials.
Term
 In AC circuits, the ___ of the flow of electric charge changes periodically, so AC and voltage in an AC circuit can be characterized by the four parameters of a sinusoidal wave: ___, ___, ___, and ___.
Definition
 polarity; wavelength, time period, frequency, and amplitude
Term
 distance between two maxima points or two minima points on a waveform is called one ___
Definition
 wavelength (λ)
Term
 “The time required for one wavelength of alternating current or one cycle of a sinusoidal acoustic wave to pass through a point is called the ___ ___”
Definition
 time period (T)-measured in seconds
Term
 “number of cycles the current waveform completes in one second and is the inverse of the time period”
Definition
 frequency (f) measured in cycles/seconds or Hz
Term
 What is the equation for frequency?
Definition
 f=1/T Hz
Term
 A good conductor almost travels at the speed of life. What is the equation for the speed of light?
Definition
 c = fλ, where c is the speed of light and l is wavelength.
Term
 The magnitude of the amplitude of an ideal DC voltage is ___. The magnitude of an AC voltage signal ___ with time.
Definition
 fixed; varies
Term
 The ________ value is the effective value of a varying voltage or current. It is the equivalent steady DC (constant) value which gives the same effect. For example, a lamp connected to a 6V RMS AC supply will shine with the same brightness when connected to a steady 6V DC supply.
Definition
 root mean square (RMS)
Term
 In our homes, the power supplied to the power mains is a ___ volt AC sinusoidal waveform with a frequency of 60 Hz. This standard is used mainly in ___ ___ and is governed by “the International Electrotechnical Commission (IEC)
Definition
 120; North America
Term
 “A ___ or a ___ ___ is a rotating vector.”
Definition
 phasor; phase vector
Term
 Although we comprehend an AC signal as a sinusoidal waveform, it can also have ___ (e.g., triangular wave, square wave, saw-tooth waveform) that are generated by certain types of digital ___ and have applications in the digital logic design industry
Definition
 shapes; oscillators
Term
 The ___ wave is the most widely used in fields such as communications, digital design, signal processing, and audio processing. These waves play an important role in technologies for generating _____ signals in modern audiometers
Definition
 square; pure-tone
Term
 A ___ ___ is a periodic mathematical function that alternates instantaneously between two levels, ideally for the same amount of time.
Definition
 square wave
Term
 “In the square wave shown in Figure 4–3, the amplitude is positive for exactly half the cycle or time period. Therefore, the signal has a ___% duty cycle. If a signal’s amplitude is positive across only one-fourth of its cycle, then the signal has a ___% duty cycle”[image]
Definition
 50; 25
Term
 “Unlike a sine wave, a square wave has more than one ___ component”
Definition
 frequency
Term
 The formula that tells you which sine-wave components are present in the square wave signal and the proportions of these components in the sine-wave signal
Definition
 Fourier transform (FFT)
Term
 “Electric power transmission refers to transmission of electricity from the generating ___ into our ___.”
Definition
 stations; homes
Term
 Because electrical transmission over long distances leads to ___ ___ by heat dissipation resulting from the resistance of the transmitting wires, the voltage carried by the transmission lines must be ___. With DC electrical transmission, this boost was accomplished using complex and expensive spinning rotary ___ (a hybrid of an AC motor and a DC generator) at regular points along the transmission line.
Definition
 power losses; boosted; converters
Term
 “Today’s AC power generators are ___-phase alternators. An alternator is an electromechanical device that converts ___ energy into ___ energy. It consists of a rotating magnet called a ___ that spins inside a coil of wires wound around a cylindrical iron core called a ___ (Figure 4–7). When the magnetic field changes due to the rotation of the ___ with respect to the wires on the stator, alternating current is induced in the coiled wires.”
Definition
 three; mechanical; electrical; rotor; stator; magnet
Term
 What is this diagram showing?[image]
Definition
 Current flow in a simple resistive DC circuit is shown in A and a simple AC circuit is shown in B. In B the solid arrows show the direction of current flow in one direction during one-half of the cycle and the dotted lines show the direction of current flow in the opposite direction during the other half of the cycle
Term
 “___ is the measure of the ability of an object to store an electric charge similar to the spring’s ability to store mechanical (potential) energy”
Definition
 Capacitance
Term
 What is the unit of capacitance?
Definition
Term
 Capacitance also can be defined as the ratio of the ___ on one conducting plate to the ____ ___ between the two plates. If these two charged plates are connected to a resistor then they will act like a ___, supplying electrical energy in the form of current to the resistor until they discharge completely. In summary, this setup of two conducting plates separated by a dielectric material forms a ___
Definition
 charge; potential difference; battery; capacitor
Term
 -A ___ is a passive component used to insert capacitance into a circuit.-“A capacitor stores electrical energy in the form of an ___ ___.”
Definition
 capacitor; electric field
Term
 “The lead wires from each plate are connected to create a ___. An ideal capacitor stores the charge accumulated on it without ___ any energy in the form of a counter-EMF (electromotive force) to resist charging by the connected source.”
Definition
 circuit; dissipating
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