What is the meaning of critical frequency?

What is the meaning of critical frequency?

Critical frequency is the highest magnitude of frequency above which the waves penetrate the ionosphere and below which the waves are reflected back from the ionosphere. It is denoted by “fc”. Its value is not fixed and it depends upon the electron density of the ionosphere.

How do you find the critical frequency?

The critical frequency is defined as(31)νc=(3e/4nmc)(E/mc2)B=16.08B(G)E2(MeV)MHz. Thus a 10-MeV electron in a 1-G magnetic field will radiate a maximum intensity near 0.29×1608MHz.

What are critical frequencies why are they so called?

Ans.) Radio frequency waves propagate between transmitter and receiver using antennas. The radio frequency at or below, the wave gets reflected from ionosphere and above this frequency waves penetrate through ionospheric layer. This is frequency is known as critical frequency.

What is difference between critical frequency and maximum usable frequency?

Though critical frequency represents highest frequency which is reflected back from the layer at vertical incidence; it is not highest frequency which is reflected from the layer. MUF (Maximum Usable Frequency) is the maximum frequency which can be reflected for given distance of transmission.

What is critical frequency in vibration?

Critical speed (nk) is the rotational speed at which acting dynamic forces cause a machine component (e. g. shaft, rotor) to vibrate at its natural frequency (also referred to as intrinsic frequency, fi) and can even result in resonant vibrations throughout the entire machine and pump set.

What is MUF and LUF?

MUF is a median frequency, defined as the highest frequency at which skywave communication is possible 50% of the days in a month, as opposed to the lowest usable high frequency (LUF) which is the frequency at which communication is possible 90% of the days, and the Frequency of optimum transmission (FOT).

What is critical frequency in control system?

The frequency at which 180 degrees PA occurs for a process (and so 360 or 0 degrees for the open loop process + controller) is called the Critical Frequency for the process.

What is the critical wavelength?

The “critical wavelength” is the wavelength below which 90% of the area under the absorbance curve resides. To claim broad-spectrum protection, the critical wavelength must be at 370 nm, or longer.

Which of the following frequency is greater than the critical frequency?

Beyond critical frequency, wave is penetrated into another region. When the frequency is greater than critical frequency, still some part is returned back by varying the angle of incidence and this frequency is called MUF.

What is optimum working frequency definition?

[′äp·tə·məm ′wərk·iŋ ‚frē·kwən·sē] (communications) The most effective frequency at a specified time for ionospheric propagation of radio waves between two specified points.

What is whirling or critical speed?

Whirling speed or Critical speed of a shaft is defined as the speed at which a rotating shaft will tend to vibrate violently in the transverse direction if the shaft rotates in the horizontal direction. In other words, the whirling or critical speed is the speed at which resonance occurs.

What is optimum working frequency?

Optimum working frequency (OWF) or Optimum traffic frequency (FOT): the lower decile of the daily values of operational MUF at a given time over a specified period, usually a month. That is, it is the frequency that is exceeded by the operational MUF during 90% of the specified period.

What is critical frequency in physics?

Critical frequency is the highest magnitude of frequency above which the waves penetrates the ionosphere and below which the waves are reflected back from the ionosphere. It is denoted by “fc”. Its value is not fixed and it depends upon electron density of ionosphere.

What is critical frequency in seismology?

Critical frequency is a step frequency between the low-frequency bandwidth and the high-frequency bandwidth. When the critical frequency in the range of 10 to 1000 kHz, the dispersion and attenuation strongly affect sonic logging and reflection seismology.

What is the critical frequency for compressional velocity?

Critical frequencies for these two cases are computed as 61.6 and 6.6 kHz, respectively. Normally, in the intermediate frequency zone between fc /10 and 10 fc, the Geerstma-Smit approximation underestimates the compressional velocity. This underestimation is identified much more strongly in low porosity and permeabliity conditions.

What is the critical frequency of the ionosphere?

Its value is not fixed and it depends upon the electron density of the ionosphere. Critical frequency can be computed with the electron density given by: where Nmax is maximum electron density per m 3 and fc is in Hz. Critical frequency can be computed by: