Many cell phones operate at 1900 MHz. Consider a cellular phone call delivered t
ID: 1613263 • Letter: M
Question
Many cell phones operate at 1900 MHz. Consider a cellular phone call delivered to a passenger in an automobile. This em wave has a maximum magnetic field strength of 1.5x10-10 T and passes perpendicularly through an open window with an area of 0.20 m2 . a) Find the wavelength of this signal. b) Find the maximum electric field strength c) Determine the intensity of the beam what enters the automobile. d) Determine how much energy this wave carried through the window of the car during a 45 second phone call.
Explanation / Answer
given
f = 1900 Mhz
= 1900*10^6 Hz
B = 1.5*10^-10 T
A = 0.2 m^2
a) c = lamda*f
==> lamda = c/f
= 3*10^8/(1900*10^6)
= 0.158 m
b) Emax = Bmax*c
= 1.5*10^-10*3*10^8
= 0.045 N/c
c)
I = Emax^2/(2*c*mue) (here c is speed of light and mue is permeability of free space)
= 0.045^2/(2*3*10^8*4*pi*10^-7)
= 2.68*10^-6 W/m^2
d) Energy transfred, E = I*A*t
= 2.68*10^-6*0.2*45
= 2.41*10^-5 J
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