Examples of frequency in the following topics:

 The perception of frequency is called pitch.
 The perception of frequency is called pitch.
 The SI unit of frequency is called a Hertz, denoted Hz.
 Different species can hear different frequency ranges.
 Three flashing lights, from lowest frequency (top) to highest frequency (bottom). f is the frequency in hertz (Hz); or the number of cycles per second.

 The lowest commonly encountered radio frequencies are produced by highvoltage AC power transmission lines at frequencies of 50 or 60 Hz.
 In this case, a carrier wave having the basic frequency of the radio station (perhaps 105.1 MHz) is modulated in frequency by the audio signal, producing a wave of constant amplitude but varying frequency.
 Other channels called UHF (ultra high frequency) utilize an even higher frequency range of 470 to 1000 MHz.
 Frequency modulation for FM radio.
 (a) A carrier wave at the station's basic frequency.

 The period is the duration of one cycle in a repeating event, while the frequency is the number of cycles per unit time.
 The frequency is defined as the number of cycles per unit time.
 Frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu).
 Note that period and frequency are reciprocals of each other .
 Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above.

 The wave resulting from the superposition of two similarfrequency waves has a frequency that is the average of the two.
 This wave fluctuates in amplitude, or beats, with a frequency called the beat frequency.
 We can determine the beat frequency mathematically by adding two waves together.
 One can also measure the beat frequency directly.
 The number of beats per second, or the beat frequency, shows the difference in frequency between the two notes.

 Response of an RLC circuit depends on the driving frequency—at large enough frequencies, inductive (capacitive) term dominates.
 Now, we will examine the system's response at limits of large and small frequencies.
 At large enough frequencies $(\nu \gg \frac{1}{\sqrt{2\pi LC}})$, XL is much greater than XC.
 The impedance Z at small frequencies $(\nu \ll \frac{1}{\sqrt{2\pi LC}})$ is dominated by the capacitive term, assuming that the frequency is high enough so that XC is much larger than R.
 Distinguish behavior of RLC series circuits as large and small frequencies

 Frequencies at which the response amplitude is a relative maximum are known as the system's resonance frequencies.
 The reactances vary with frequency $\nu$, with XL large at high frequencies and XC large at low frequencies given as:
 $\nu_0$ is the resonant frequency of an RLC series circuit.
 A variable capacitor is often used to adjust the resonance frequency to receive a desired frequency and to reject others. is a graph of current as a function of frequency, illustrating a resonant peak in Irms at $\nu_0 = f_0$.
 An RLC series circuit with an AC voltage source. f is the frequency of the source.

 Looked at from another point of view, for any sampling interval $\Delta$ , there is a special frequency (called the Nyquist frequency), given by $f_s = \frac{1}{2\Delta}$ .
 The extrema (peaks and troughs) of a sinusoid of frequency $f_s$ will lie exactly $1/2f_s$ apart.
 Figure 4.9 shows a cosine function sampled at an interval longer than $1/2f_s$ ; this sampling produces an apparent frequency of 1/3 the true frequency.
 This means that any frequency component in the signal lying outside the interval $(f_s,f_s)$ will be spuriously shifted into this interval.
 Figure 4.9: A sinusoid sampled at less than the Nyquist frequency gives rise to spurious periodicities.

 The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
 The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
 When tuning a radio, for example, people are adjusting the resonant frequency of the radio circuit so that it only oscillates to the desired station's broadcast (or driving) frequency.
 Resonance occurs when the driving frequency equals the natural frequency, and the greatest response is for the least amount of damping.
 Heavy cross winds drove the bridge into oscillations at its resonant frequency.

 Extremely high frequency (EHF) is the highest microwave frequency band.
 Super high frequency (SHF) is the designation for electromagnetic wave frequencies in the range of 3 GHz to 30 GHz.
 Microwaves at a frequency of 2.45 GHz are produced by accelerating electrons.
 The maser, rather than amplifying visible light energy, amplifies the lowerfrequency, longerwavelength microwaves and radio frequency emissions.
 The range of frequencies and wavelengths is remarkable.

 Since the time between waves is reduced, the frequency is increased.
 If the observer is moving away from the sound source, the frequency will be lowered, and if the observer moves closer to the sound source, the frequency is increased.
 If the source approaches the observer at an angle (but still with a constant velocity), the observed frequency that is first heard is higher than the object's emitted frequency.
 If the speeds and are small compared to the speed of the wave, the relationship between observed frequency and emitted frequency is approximately
 The wavefronts are produced with the same frequency as before.