1. Red light with a wavelength of 745 nm has what frequency? If the maximum elec
ID: 1549161 • Letter: 1
Question
1. Red light with a wavelength of 745 nm has what frequency? If the maximum electric field in this EM wave is 25 N/C then what is the energy density of the wave?
2. A speeder is puller directly away and increasing his distance from a police car that is moving at 25 m/s with respect to the ground. The radar gun in the police care emits an electromagnetic wave with a frequency of 7.0 x 10^9 Hz. The wave reflects from the speeder's car and returns to the polic care, where its frequency is measured to be 320 Hz less than the emitted frequency. Find the speeder's speed with respect to the ground.
3.Light that is polarized along ther verticle direction is incident on a sheet of polarizing material. Only 94% of the intensity of the light passes through the sheet and strikes a second sheet of polarizing material. No light passes through the second sheet. What angle does the transmission axis of the second sheet make with the vertical?
Explanation / Answer
1.
= c/f = (3.0*10^8)/(745*10^-9) = 4.03*10^14 Hz
energy density S=Emax2/(2cµ0) = (25)/(2*3*10^8*8.85*10^-12) = 4708.1 J/m^3
2.
Use equation,
v/c = f/f
v =c* f/f
vspeeder – vpolice =c* f/f
vspeeder = vpolice +[c* f/f ]
vspeeder = 25+[(3*10^8*320)/(7.0*10^9)]
vspeeder = 38.7 m/s
3.
If = Ii*cos2
If /Ii= cos2
cos = If /Ii
=cos^-1[If /Ii] = cos^-1(0.94) = 20 deg
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