A stationary source of wave emissions propagates those waves into space at a constant given frequency which will be perceived by a stationary observer at the frequency at which the waves were emitted, taking into consideration the effect of the medium through which the waves travel. An object, moving with respect to an observer at a velocity less than that of the wave it emits, creates a change known as the Doppler Effect in its perceived output. The waves emitted from this source continue their expansion at a constant rate from the source's original location so that the center of each wavefront is shifted according to direction and velocity. Should the observer and source be approaching each other's position, the wavelengths become shorter and the frequency becomes higher with a subsequent apparent sensory effect, the reverse being true should the two be moving away from each other. The total Doppler Effect, therefore, may be used to detect the velocity and direction of any object which emits waves, if enough information is available about the state of the observer and the medium through which the waves are propagated. For instance, the electromagnetic radiation emitted by objects in space outside our galaxy exhibits a definite redshift, those objects farther away from us being more redshifted than those closer to us, whereas objects within our galaxy may exhibit blue or redshifts. Edwin Hubble used these facts to argue that the universe is constantly expanding, carefully noting that taking the same readings from any location in the universe would result in the same findings.
1. Which of the following is suggested about redshifts?
A. A redshift shows that an object which emits waves is moving away from an observer.
B. A redshift is an indicator of the distance between an object and its observer.
C. A redshift is the result of a higher frequency of waves than that which the source originally emitted reaching the observer.
D. A redshift occurs when the distance between a moving source of waves and a stationary observer increases.
E. An object is more redshifted the greater the distance between that object and an observer.
OA is A
2. It may be inferred that a moving observer could perceive the waves emitted by a moving object
A. at a velocity other than their real velocity
B. unless the object is traveling faster than the waves it emits
C. unless the medium through which the waves travel interferes
D. as if the object were stationary
E. unless the two are traveling away from each other at a speed different than the speed of the waves emitted by the object
OA is D
very hard science passage for me
Eliminated A in the first place for 1st qn
Can someone help us to understand the passage?
