A) The U.S. Navy has long proposed the construction of extremely low-frequency (
ID: 1352633 • Letter: A
Question
A) The U.S. Navy has long proposed the construction of extremely low-frequency (ELF waves) communications systems; such waves could penetrate the oceans to reach distant submarines. Calculate the length of a quarter-wavelength antenna for a transmitter generating ELF waves of frequency 89 Hz.
How practical is this antenna?
practical /not practical
B) A diathermy machine, used in physiotherapy, generates electromagnetic radiation that gives the effect of "deep heat" when absorbed in tissue. One assigned frequency for diathermy is 27.33 MHz. What is the wavelength of this radiation?
C) What are the wavelength ranges for the following?
the AM radio band (540-1600 kHz)
m (maximum wavelength)
m (minimum wavelength)
the the FM radio band (88-108 MHz)
m (maximum wavelength)
m (minimum wavelength)
Explanation / Answer
length of transmitting antenna = L/4 = C/4f
L = 3e8/(4* 89)
L = 842.7 Km
--------------------------------
So high length is not feasible, so it not practical
-------------------------------------
use the relatio between wavelength l , speed V and frequency f as
V = Lf
so
L = 3e8/27.33 e 6
L = 11m
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C. Lmax = V/f = 3e8/540 = 555.55 km
L min = V/f = 3e8/1600000 = 187.5 m
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