b) When viewed by an observer on the Earth, light from adistant galaxy is Dopple
ID: 1673993 • Letter: B
Question
b) When viewed by an observer on the Earth, light from adistant galaxy is Doppler shifted to the red such that the ratio ofthe unshifted frequency to the observed frequency is 1.5. What is the galaxy's speed relative to theEarth?1c
a) We know from experience that the Doppler shift of soundfrom a moving car is easily detectable. Assuming light with afrequency of 7.0 1014 Hz, estimate the Doppler shift forlight from a car moving toward you at a speed of35 m/s (about 78.4 mi/h). 1 Hz b) When viewed by an observer on the Earth, light from adistant galaxy is Doppler shifted to the red such that the ratio ofthe unshifted frequency to the observed frequency is 1.5. What is the galaxy's speed relative to theEarth? 1c c)Unpolarized light with intensity I0 isincident on two polarizers as sketched in the figure below. Supposethe angle between the axes of the two polarizers is theta = 68 degree. What is the intensity ofthe transmitted light? Express your answer as a fraction ofI0. I2 = xI0
Explanation / Answer
Doppler shift for light from a car moving f'-f=f*(c/(c-v)-1)=81.7*106 Hz (b) the galaxy's speed relative to the Earth f'/f=1/(1-v2/c2)*(1+v/c)=3/2 => 4*(1+2x+x2)=(1-x2)*9 13x2 +8x-5=0 x=0.38 c I=Io/2*cos682=0.07Io I=Io/2*cos682=0.07IoRelated Questions
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