Unpolarized light of intensity l_0 passes through three polarizing filters. The

Question

Unpolarized light of intensity l_0 passes through three polarizing filters. The polarization axis of the first polarizer is vertical. The second polarizer axis makes and angle theta with the vertical. The third polarizer is also vertical. Let l_0 = 8.00 w/m^3 and theta = 45 degree Find the intensity of the light the light after it passes through the three. 1.41 w/m^2, 1.35 W/m^2 1.21 w/m^2 1.00 w/m^2 Two police cars are approaching each other with speed v. Their sirens have a frequency f. Let v = 45 m/s, f_s= 270 Hz, and the speed of sound in air that day is c = 345 m/s. Find the frequency of the siren of the left car as is heard by the policewoman in the right car. 294 Hz, 311 Hz, 351 Hz, 305 Hz

Explanation / Answer

19
Given

the three polarizers are of theta = 45 degrees, intensity I0 = 8 w/m2

now the intensity of light after came out from the first polarizer is

   I1= I0/2= 4 W/m2

and from the second polarizer which is of angle 45 degrees

   I2 = I1 cos ^2 theta = 4cos ^2 45 = 4*0.5 = 2 W/m2

and
from the third polarizer
   I3 = I2 cos ^2 theta = 2cos ^2 45 = 2*0.5 = 1 W/m2

so the answer is option d 1 W/m2

20.

we know that the two cars are approaching each other with speeds 45 m/s

and the frequency of the horn is f = 270 Hz

from the doppler effect the apparent change in frequency f' = f((v+v0)/(v-vs))

substituting the values the frequency heard by the police in the right car is

           f' = 270(345+45/345-45)Hz

           = 351 Hz

the answer is option C ------------->>> answer

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